Form 4 Physics Chapter 5

Physics Module Form 4 Chapter 5 - Light GCKL 2011

5 - 1

U N D E R S T A N D I N G R E F L E C T I O N O F L I G H T

What light is? Is a form energy. Light travel in a straight line and high speed about 300,000 km s-1

.

How the light

ray reflected

by the surface

of mirror?

1. The light ray that strikes the surface of

the mirror is called incident ray.

2. The light ray that bounces off from the

surface of the mirror is called reflected ray.

3. The normal is a line perpendicular to

the mirror surface where the reflection

occurs.

4. The angle between the incident ray and

the normal is called the angle of incidence

,i.

5. The angle between the reflected ray and

the normal is called the angle of

reflection, r.

AO = incident ray

OB = reflected ray

i = angle of incident

r = angle of reflected

What is the

Law of

Reflection ?

The Laws Of Reflection

1. The incident ray, the reflected ray and the normal all lie in the same plane The angle of

incident, i, is ….equal….. to the angle of reflection, r.

Draw the ray

diagram of the

plane mirror

1. Consider an object O placed in front of a

plane mirror.

2. Measure the distance between the object

o and the mirror.

3. Measure the same distance behind the

mirror and mark the position as the image.

4. Draw the diverging ray from a point on

the image to the corner of the eye. The rays

from the image to the mirror must be

dotted to show that are virtual.

5. Finally, draw two diverging rays from

the object to the mirror to meet the

diverging rays from the image.

5.1


5 - 2

State the

characteristics

of the image

formed by

plane mirror

1 laterally inverted

2. same size as the object

3. virtual

4. upright

5.distance between image and mirror same

as distance between object and mirror.

What is meant

by virtual

image?

Image that …cannot………. be seen on a screen.

What is meant

by real image?

Image that …...can…be seen on a screen.

CURVED MIRRORS:

Concave mirror Convex mirror

State the

differences

between

concave mirror

and convex

mirror

1.Light (diverged, converged)

2.(virtual,real) principal focus

3.PF = Focal length

= Distance between the virtual

principal focus and the pole of the

mirror.

1.Light (diverged, converged)

2. (virtual,real) principal focus

3. PF= ….Focal length…

= Distance between the real principal focus

and the pole of the mirror.

Common

terminology of

reflection of

light on a

curved mirror

Refer to the diagrams above and give the names for the following:

1.Centre of curvature ,C = The geometric centre of a hollow sphere of which the concave or

convex mirror is a part.

2.Pole of mirror, P = The centre point on the curved mirror

3.Radius of curvature ,r = CP = radius of the curvature

4.Focal length, f = The distance between the principle focus, F and the pole of the mirror, P

5.Object distance, u = Distance of object from the pole of the mirror, P

6.Object distance , v = Distance of image from the pole of the mirror,P

Construction

Rules for

Concave

Mirror

Ray 1 Ray 2

Ray 3

f

r

f

r


5 - 3

A ray parallel to the

principle axis is reflected to

pass through F.

A ray through F is reflected

parallel to the principle

axis.

A ray through C is reflected

back along its own path.

Image formed

by concave

mirror:

Using the principles of construction of ray diagram, complete the ray diagrams for each of the

cases shown below:

u = object distance; v = image distance ; f = focal length ; r = radius of curvature

Note: Point of intersection in the position of the image

A u < f ( Object between F and P ) Characteristics of

image:

1.virtual

2.upright

3.magnified

Application:

1.magnifying mirror

2.sharing mirror

3. make-up mirror

B u = f ( Object, O is at F ) Characteristics of

image:

1.Image at infinity

Application:

A reflector to

produce parallel

beam of light

such as a reflector in

1. torchlight

2.spotlight

C f < u < 2f or f < u < r ( Object O is

between F and C

Characteristics of

image:

1.magnified

2.real

3.inverted

D u = 2f or u = r ( Object ,O is at C) Characteristics of

image:

1.same size

2.real

3.inverted

Application:

1.reflector in a

projector

I


5 - 4

Eu > 2f or u > r ( Object, O is beyond C ) Characteristics of

image:

1.diminished

2.real

3.inverted

F u = ( Object ,O very far from the lens) Characteristics of

image:

1.diminished

2.real

3.inverted

Application:

Used to view distant

objects as in a

reflecting telescope

Construction

Rules for

Concave

Mirror

Ray 1

Ray 2 Ray 3

A ray parallel to the

principal axis is reflected as

if it came from F.

A ray towards F is reflected

parallel to the principal

axis.

A ray towards C is reflected

back along its own path.

Image formed

by concave

mirror:


cases shown below:

u = object distance; v = image distance ; f = focal length ; r = radius of curvature


image:

1.diminished

2.virtual

3.upright

Application:

1. Blind Conner

mirror

2.Wide side view

mirror

I

I


5 - 5

Check Yourself:

Objective Question:

1. Which of the following is true of the laws of

reflection f light?

A The angle of incident is equal to the

angle of refraction

B The incident ray and the reflected ray

are always perpendicular to each

other.

C The incident ray , the reflected ray

and the normal line through the point

of incidence, all lie on the same plane.

2. The diagram shows a single ray of light being

directed at a plane mirror.

What are the angles of incidence and reflection?

Angle of incidence Angle of

reflection

A 40o 40

o

B 40o 50

o

C 50o 40

o

D 50o 50

o

3. The diagram shows a ray of light from a small bulb

strikes a plane mirror.

Where is the image of the bulb formed and its

characteristic?

A At P and virtual

B At Q and real

C At R and virtual

4. A boy stands in front of a plane mirror a distance

5 m . When the boy moves toward the mirror by 2

m , what is the distance between the boy and his

new image?

A 2m B 4m

C 6m D 8 m

E 10 m

5. An object is placed in front of a plane mirror.

Compare to the object, the image formed in the

mirror is always

A virtual

B smaller

C bigger

D three times as far away

6. A light ray incident onto a plane mirror at an

angle of 50o

The characteristics of an image , formed by a

convex mirror for all positions of the object are

A diminished, real and inverted

B magnified , real, and upright

C diminished ,virtual and upright

D magnified , virtual and inverted

7. A concave mirror has a focal length 20 cm.

What happen to the size of image when an object

is placed at a distance of 40 cm in front of the

mirror?

A diminished

B magnified

C same size of object

40°


5 - 6

8. The figure shows a candle placed in front of a

concave mirror of focal length, f.

The image formed is

A real, upright and magnified

B real, inverted and diminished

C virtual, inverted and magnified

D virtual, upright and diminished

9. When an object is placed at a point 20 cm in

front of a concave mirror, a real image of the

same as the object is formed on a screen placed

next to the object. What is the focal length of the

mirror?

A 5 cm

B 10 cm

C 15 cm

D 20 cm

10. Which of the following states the right reason for

replacing a plane mirror are used as rear- view

mirrors in motor vehicles with a convex mirror ?

A To shine the object

B To widen the field of view

C To produce a brighter image

D To produce a sharper image

Answer:

1 C

2 D

3 A

4 C

5 A

6 C

7 A

8 A

9 B

10 C

Section A (Paper 2)

Structure Question:

1. Diagram 3.1 shows a mirror at the corner of a shop.

DIAGRAM 3.1 / RAJAH 3.1

(a) Name the type of mirror shown in Diagram 3.1

Convex mirror

……………………………………………………..

[1 mark]

(b) Name one characteristic of the image formed

by the mirror.

Upright / diminished / smaller / virtual

……………………………………………………..

[1 mark]

(c) Sketch a ray diagram to show how the image

is formed.

1. Draw a parallel ray from the object that is

incident along a path parallel to the principal axis

appears to go through the focal point

2. A radial ray that is incident through the centre

of curvature, C of the curved mirror is reflected

back along the incident path through point C

3. Determine the correct position of the image

[3 marks]

(d) What is the advantage of using this type of

mirror in the shop?

To increase the field of vision

……………………………………………………………

[1 mark]


5 - 7

2. Diagram 4.1 shows the image of a patient’s teeth

seen in a mirror used by a dentist.

DIAGRAM 4.1

(a) Name the type of the mirror used by the

dentist.

Concave mirror

………………………………………… …….

[ 1 mark ]

(b) State the light phenomenon that causes the

image of the teeth

Reflection of light

………………………………………………..........

[ 1 mark ]

(c) State two characteristics of the image

formed.

Virtual, upright and magnified

…………………………………………………….

[ 2 marks ]

(d) In the diagram below, the arrow represents

the teeth as the object of the mirror.

Complete the ray diagram by drawing the

required rays to locate the position of

the image.

[ 3 marks]

Section B(Paper 2)

Essay Question(20 marks)

Diagram 7.1 shows two cars, P and Q , travelling in

the opposite directions, passing through a sharp band.

A mirror is placed at X .

DIAGAM 7.1

(a) Diagram 7.2 shows an incomplete ray

diagram when a plane mirror is placed at X.

DIAGRAM 7.2

(i) Complete the ray diagram in Diagram 7.2

[2 marks]

1. Two reflected rays are shown (diagram)[1 mark]

2. Angle of incidence = Angle of reflection (diagram)

[1 mark]


5 - 8

(ii) State the light phenomenon involved in (a)(i).

Reflection

…………………………………………………

[1 mark]

(iii) Based on your answer in (a)(i), state the problem

experienced by the driver in car P.

The driver in car P cannot see car Q // field of

………………………………………………………..

view very small

………………………………………………………..

[1 mark]

(b) Diagram 7.3 shows an incomplete ray diagram

when a curve mirror is placed at X to replace the

plane mirror in Diagram 7.2. The curve mirror is used

to overcome the problem that occur in (a)(iii).

DIAGRAM 7.3

(i) Give the name of the curve mirror.

Convex mirror

…………………………………[1 mark]

(ii) Complete the ray diagram in Diagram 7.3

[2 marks]

1. Two reflected rays are shown (diagram)[1 mark]

2. Angle of incidence = Angle of reflection (diagram)

[1 mark]

(iii) Based on your answer in b(ii), how the curve

mirror solved the problem in (a) (iii)?

The convex mirror increase the field of view

…………………………………………………….

[1 mark]

( C) The characteristics of the image formed by the

curved mirror in Figure 7.3 is diminished,

virtual and upright.

(i) What happen to the characteristics of the

image when the focal length of the curved mirror

is increased?

The driver in car P cannot see car Q // field of

………………………………………………………..

view very small

………………………………………………..

[1 mark]

(ii) Give the reason for your answer in (c)(i).

The characteristics of image of a convex

……………………………………………………..

mirror not depends on the focal length

…………………………………………………

[1 mark]


5 - 9

U N D E R S T A N D I N G R E F R A C T I O N O F L I G H T

The diagram shows the spoon bent when put inside the water.

State the

phenomenon

occurs.

Refraction of light

How the

phenomenon

occurs?

Light travel from less dense medium which is air to denser medium (water), light will be

deviated near to the normal. Thus the spoon seems like bending after putting inside the water.

Why light is

refracted?

It due to change in the velocity of light as it passes from one medium into another.

Light travel more slowly in water (or glass) than in air.

When a light beam passes from air into glass, one side of the beam is slowed before the other.

This makes the beam ‘bend’.

Three different

cases of refraction

Case 1:

i = 0 ,r = 0

Case 2:

i > r

Case 3:

i < r

5.2


5 - 10

When a ray of light crosses

the boundry between two

different mediums at a right

angle or the incident ray

parallel to normal,

the ray is not bent

but the speed of

light is different.

The angles of

incidence and

refraction are zero.

Ray is light passes from

air(less dense) to

glass(denser).

ray is bent towards

the normal

the speed of light

decreases after

entering the glass

Ray of light passes from

glass(dense) to air(less

dense)

ray bent away from

the normal

the speed of light

increases after

emerging from the

glass.

State the Laws of

Refraction

The Laws Of Refraction

When the light travel from one medium to another medium which has a different optical density:

1. Snell’s Law :The ratio of the sine of the angle of incidence to the sine of the angle of

refraction is constant.

2. The incident ray, the normal and the refracted ray all lie in the same plane

Refractive Index

1. When light travels between two mediums with different optical densities, it changes speed

and bends.

2. The speed of light will decrease when it enters an optically denser medium and increases when

it enters an optically less dense medium.

3. The angle of bending of light depends on the refractive index of the mediums and the angle of

incidence ,i.

How to define

refractive index

1. Refractive index, n is defined as,

where n = Refractive index

i = the angle in medium less

dense

r = the angle in denser medium

A material with a higher

refractive index has a higher

density.

The value of refractive index , n

1

The refractive index has no units.

Example:

The diagram shows a ray of light passing from

air to the block X.

Calculate the refractive index of the block X.

Solution:

n = sin 50°

sin 40°

= 1.2

n = sin i

sin r


5 - 11

2.

Example:

The speed of light in vacuum is 3 x 108 ms-1

and the speed of light in glass is 2 x 108 ms-1 .

Determine the refractive index of glass.

Solution:

n = 3 x 108 ms-1

2 x 108 ms-1

= 1.5

3.Real Depth and Apparent Depth

The following terms are defined:

Real depth,H = The distance of the real object,

O from the surface of the water.

Apparent depth, h= The distance of the image,

I from the surface of the water.

The refraction of light gives us a false

impression of depth.

Example:

A) The fish in the pond appears to be closer to

the surface than it actually is.

(B) The apparent depth – a swimming pool

looks shallower than it really is.

n = speed of light in vacuum (air)

speed of light in medium

0r

n = va

vm

n = Real depth , H

Apparent depth, h

Or

n = H

h


5 - 12

( C) A straight object place in water

looks bent at the surface.

Explanation:

1.Rays of light from the object travel from

water to air.

2.Water is a denser medium compared to air.

3. Therefore, rays of light refract away from

the normal as they leave the water. The rays of

light then enter the eyes of the observer.

4. So the object appears to be nearer the

surface of the water.

Experiment to investigate the relationship between the

angle of incidence and the angle of refraction.

Hypothesis:

The angle of refraction increases as the angle of

incidence increases.

Aim of the experiment :

To investigate the relationship between the angle of

incidence and the angle of refraction.

Variables in the experiment:

Manipulated variable: Angle of incidence

Responding variable: Angle of refraction

Fixed variable: Refractive index

List of apparatus and materials:

Glass block, ray box, white paper protactor, power

supply .

Experiment to investigate the relationship between

real depth and apparent depth.

Hypothesis:

The apparent depth increases as the real depth increases.

.

Aim of the experiment :

To investigate the relationship between apparent depth

and the real depth

Variables in the experiment:

Manipulated variable: real depth

Responding variable: apparent depth

Fixed variable: Refractive index

List of apparatus and materials:

Pin, ruler, water, retort stand ,tall beaker


5 - 13

Arrangement of the apparatus:

The procedure of the experiment which include the

method of controlling the manipulated variable and

the method of measuring the responding variable.

The glass block is placed on a white paper.

The outline of the sides of the glass block are traced on

the white paper and labelled as ABCD.

The glass block is removed.

The normal ON is drawn.

By using a protractor , the angle of incidence, i , is

measured = 20°.

The glass block is replaced again on its outline on the

paper.

A ray of light from the ray box is directed along

incidence line.

The ray emerging from the side CD is drawn as line PQ.

The glass block is removed again.

The point O and P is joined and is drawn as line OP.

The angle of refraction, r is measured.

The experiment is repeated 5 times for the other angles of

incidence, i= 30° , 40°,50°, 60° and 70°.

Tabulate the data:

Sin i

Sin r

Analysis the data:

Plot the graph Sin r against Sin i

Arrangement of the apparatus:

The procedure of the experiment which include the

method of controlling the manipulated variable and

the method of measuring the responding variable.

A pin is placed at the base of the beaker as object O.

The another pin is clamped horizontally onto the retort

stand as image position indicator, I

The beaker is filled with water.

By using a ruler ,the real depth of the pin is measured, H=

8.0 cm

The pin O is seen vertically above the surface of the

water.

The position of pin I is adjusted until parallax error

between the pin O and the pin I is non- existent.

By using the ruler again ,the position of pin I is measured

as the apparent depth = h

The experiment is repeated 5 times for the other value of

the real depth of water, ,i.e. D=10 cm,12 cm,14 cm and

16 cm.

Tabulate the data:

H/cm

h/cm

Analysis the data:

Plot the graph h against H


5 - 14

Check Yourself:

Objective Question:

1 When light travels from one medium to another,

refraction take place. Refraction is caused by the

change in the

A amplitude of light rays

B intensity of light rays

C strength of light rays

D velocity of light rays

2 An observer cannot see the coin in an empty glass

as shown in Figure(a). However , he can see the

coin when the glass is filled with water as shown

in Figure(b).

Figure (a)

Figure (b)

The observer can see the coin in Figure (b) due to

A the total internal reflection of light

B the refraction of llight

C the reflection of light

D the diffraction of light

3 Which of the following is not caused by the

refraction of light ?

A A fish in pond appears nearer to the surface

of the water

B The sunlight reaches to the earth in a curve

path

C A ruler appears to bend at the water surface.

D The sea water appear in blue colour

4 Figure shows a light ray travelling from

medium R to medium S.

Which of the following is true?

A The speed of light in medium R is larger than

the speed of light in medium S

B The optical density of medium R is larger

than the optical density of medium S

C The refractive index of medium R is larger

than the refractive index of medium S

5 The diagram shows a light ray directed into a

glass block.

Which is the angle of refraction?

6 A light ray travels from medium P to medium Q.

Which of the following diagrams correctly shows

the path of the light ?

[ Medium P denser medium and Medium Q less

dense ]


5 - 15

7 The diagram shows a light ray travels from liquid

L to liquid M.

Which of the following diagrams correctly shows

the path of the light ?

[ Refractive index of liquid M > Refractive index

of liquid L ]

8 The diagram shows a light ray which travels from

the air to the glass.

What is the refrective index of the glass?

A Sin S B Sin P

Sin Q Sin R

C Sin Q D Sin R

Sin R Sin S

9 Which of the following formulae can be used to

determine the refractive index of a medium?

A Angle of incidence

Angle of refraction

B Apparent depth

Real depth

C Speed of light in vacuum

Speed of light in the medium

10 The diagram shows a light ray travels from the air

into medium X.

What is the refractive index of medium X?

A 0.85

B 1.24

C 1.31

D 1.41

E 1.58

11 The diagram shows a light ray travels from the oil

into the air.

What is the value of k?

[ Refractive index of oil = 1.4 ]

A 44.4o

B 45.6o

C 54.5o

D 55.4o

E 58.9o

12 The diagram shows a light of ray travels from the

air into a glass block.


5 - 16

What is the refractive index of the glass block?

A 1.38

B 1.45

C 1.51

D 1.62

E 1.74

13 The speed of light in the air is 3 x 108 ms-1 .

What is The speed of light in a plastic block?

[ Refractive index of plastic = 1.2 ]

A 1.0 x 108 ms-1

B 1.5 x 108 ms-1

C 2.0 x 108 ms-1

D 2.5 x 108 ms-1

E 3.0 x 108 ms-1

14 The diagram shows a boy appearing shorter when

he is in a swimming pool. The depth of the water

in the pool is 1.2 m.

[ Refractive index of water = 1.33 ]

What is the apparent depth of the pool?

A 0.1 m B 0.3 m

C 0.9 m D 1.1 m

E 1.6 m

15 The diagram shows a coin is put at the base of

the beaker. The image of the coin appears to be 5

cm from the base of the beaker.

What is the refractive index of the liquid?

A 8 B 5

13 8

C 11 D 13

5 8

E 19

14

Answer:

1 D 11 A

2 B 12 C

3 D 13 D

4 A 14 C

5 D 15 D

6 C 16

7 B 17

8 C 18

9 D 19

10 A 20


5 - 17

Section A

(Paper 2)

Structure Question:

1. The Diagram shows a side view of a water-filled

aquarium RSTU. An electric lamp, surrounded by a

shield with a narrow transparent slit, is immersed in

one corner of the aquarium at U. The light ray from

the slit shines on the water surface RS at an angle of

40o as shown in diagram below.

[2 ma

(a) What is meant by refractive index of a

substance?

Refractive index is an indication of the light

bending ability of the medium /

n = sin i

sin r [1 mark]

(b) If the refractive index of water is 1.33,

calculate the critical angle for a ray travelling

from water to air.

n = 1

sin c

sin c = 1

1.33

c = 48.80 [ 2 marks]

(C ) (i) Draw a Diagram of the light ray shown on

diagram 3.1, meeting the water surface RS, and show

its path after meeting the surface. [1 mark]

ii. Calculate the angle that this new path makes with

RS and label the angle. [1 mark]

Angle = 40o

(d) The lamp is then placed outside underneath

the aquarium with the light striking to the bottom of

the aquarium as shown in Diagram 3.2. Draw the light

ray on Diagram 3.2, after striking the aquarium.

[1 mark]

DIAGRAM 3.1

Aquarium 40o

R S

T U

Light

ray

Water

Lamp

Light ray

water

40o

T U

S R

Light ray

Water 40o


5 - 18

2. An observer is looking at a piece of coin at the bottom of a glass filled with water as shown in Diagram 3. He found that the image of the coin is nearer to the surface of the water.

[

2

m

a

r

k

s

]

(a)(i) State a characteristic of image in Diagram 3.

Virtual/magnified [1 mark]

]

(ii) Name the science phenomenon involve in the observation above. [1 mark]

Refraction

(b) Explain why the image of the coin

appears nearer to the surface of the

water.

- Light ray travels from density to less

density medium

- Refracted ray away from normal

[2 marks]

(c) On Diagram 3, complete the ray

diagram from the coin to the observer's

eye. [2 marks]

-Draw refracted ray correctly - Draw ray from image to the

observer

[

1

]

3. Figure(a) shows an object in a small pond. The

depth of the water in the pond is H. The image

of the objet appears to be h from water surface.

Figure(a)

(a) State the relationship between H and h

When H increases, h increases/ H is directly

proportional to h

....................................................................

(b) When H = 4.5 m and the refractive index of

water is 1.33, determine the value of h .

n = Real depth , H

Apparent depth, h

1.33 = 4.5 m

H

H = 3.38 m

(c) What happen to value of h when the pond is

poured with water of refractive index 1.40 ?

H decreases

……………………………………………


5 - 19

Section B (Paper 2)

Essay Question

1. Figure 4(a) shows a pencil placed in a glass of

water. Figure 4(b) shows the appearance of print

viewed from the top of a thick block of glass placed

over it.

(a) i. Why does the pencil appear bent to our eyes?

Why does the print appear raised?

[1 mark]

Answer:

We can see the pencil and the print because the rays

of light from the two objects reach our eyes.

ii. Observe Figure 4(a) and Figure 4(b) carefully.

Compare the common characteristics of the pencil

and the print before and after they are removed

from the water and the glass block respectively.

Use a physics concept to explain the appearance

of the pencil and the print in water and under the

glass block respectively.

[5 marks]

Answer:

1. The pencil appears bent when placed in water

and the print appears raised when a thick block of

glass is placed over it.

2. The rays of light from the pencil are refracted away

from the normal as they leave the water and enter the

eye of the observer. These rays appear to come from a

virtual image above the actual point. The pencil

,therefore , appears bent in the water.

3. Rays of light from the print below the glass are

refracted away from the normal as they leave the glass

and enter the aye of the observer . The writing,

therefore, appears to be slightly raised.

4. Refraction of light is the physics concept involved.

5. Refraction of light is a phenomenon in which rays of

light change direction when they pass from one

medium to another medium of a different density.

pencil

water

Glass block

Figure 4(a) Figure 4(b)


5 - 20

UNDERSTANDING TOTAL INTERNAL REFLECTION

What is meant by

total internal

reflection?

Total internal reflection is the complete reflection of light ray travelling from a denser medium to

a less dense medium.

Total: because 100% of light is reflected

Internal: because it happens inside the glass or denser medium.

What is meant by

critical angle ,c?

The critical angle, c, is defined as the angle of incidence (in the denser medium) when the angle

of refraction (in the denser medium), r is 90°.

What are the

relationship

between the

critical angle and

total internal

reflection ?

5.3


5 - 21

When the angle of

incidence, i keeps on

increasing, r too

increases

And the refracted ray

moves further away

from the normal

And thus approaches

the glass- air

boundary.

The refracted ray

travels along the

glass-air boundary.

Angle of refraction, r

= 90°.

This is the limit of

the light ray that can

be refracted in air as

the refracted in air

cannot be any larger

than 90°.

The angle of

incidence in the

denser medium at the

limit is called the

critical angle, c.

If the angle of

incidence is

increased is

increased further so

that it is greater than

the critical angle,

(i > c):

- no refraction

- all the light is

totally in the

glass

This phenomenon is

called total internal

reflection.

State the two

conditions for

total internal

reflection to occur

1. light ray enters from a denser medium towards a less dense medium.

2. the angle of incidence in the denser medium is greater then the critical angle of the medium

( i > c)

What are the

relationship

between the

refractive index, n

and critical angle,

c?

What are the

phenomena

involving total

internal reflection?

1. Mirage

In hot days, a person traveling in a

car will see an imaginary pool of

water appearing on the surface of

the road.

The layes higher up are cooler and

denser.

Light ray from the sky travels from

denser to less dense medium and


5 - 22

will refracted away from the normal.

The angle of incidence increases

until it reach an angle greater than

the critical angle.

Total internal reflection occurs and

the light is reflected towards the aye

of the observer.

If the observer’s eye is in the correct

position, he will see a pool of

water(image of the sky) appearing

on the road surface.

This is known as a mirage.

2. Rainbow

When sunlight shines on millions of

water droplets in the air after rain, a

multi coloured arc can be seen.

When white light from the sun

enters the raindrops, it is refracted

and dispersed into its various colour

components inside the raindrops.

When the dispersed light hit the

back of the raindrop, it undergoes

total internal reflection.

It is then refracted again as it leaves

the drop.

The colours of a rainbow run from

violet along the lower part of the

spectrum to red along the upper part.


5 - 23

Give some

examples of

application of total

internal reflection.

1. The sparkling of a diamond

A diamond has a high refractive

index.

The higher the refractive index, the

smaller the critical angle.

A small critical angle means total

internal reflection readily occurs.

Light is easily reflected inside the

diamond.

In this way, more light will be

confined within the diamond before

refracting out into the air.

2. Periscope

The periscope is built using two

right angled 45° made of glass. The

critical angle of the prism is 42°.

The angle of incidence is 45° which

is greater than the critical angle.

Total internal reflection occurs.

The characteristics of the image are:

Virtual, upright, same size.

Give the advantages of the prism periscope

compared to mirror periscope.

Answer:

(i) The image is brighter because all the light

energy reflected.

(ii) The image is clearer because there are no

multiple images as formed in a mirror

periscope.


5 - 24

3. Prism Binocular

A light ray experiences two total

internal reflections at each prism.

So the final image in binoculars is

virtual, upright and same size.

What are the benefits of using prism in

binoculars?

(a) an upright image is produced.

(b) The distance between the objective lens

and the eyepiece is reduced. This make the

binoculars shorter as compared to a

telescope which has the same magnifying

power.

4. Optical Fibres

The external wall of a fibre optic is

less dense than the internal wall.

When light rays travel from a

denser internal wall to a less dense

external walls at an angle greater

than the critical angle, total internal

reflection occurs.

Give the advantage of using optical fibres

cables over copper cables.

(1) they are much thinner and lighter.

(2) a large number of signals with very little

loss over great distances.

(3) The signals are safe and free of electrical

interference


5 - 25

(4) It can carry data for computer and TV

programmes.

Check Yourself:

Objective Question:

1 A ray of red light travelling in glass strikes the

glass-air boundary . Some light is reflected and

some is refracted. Which diagram shows the paths

of the rays?

2 One of the diagram below shows the path of a

beam of

light that is incident on a water-air surface with

angle of incidence greater than the critical angle.

Which one is it?

3 Which of the following diagram correctly shows

the total internal reflection of ray of light?

[ Refractive index of medium X = 1.3

Refractive index of medium Y = 1.5 ]

4 Which of the following shows total internal

reflection?

5 The diagram shows light ray XO experiencing

total internal reflection when travelling from the

glass to air.

Which statements about total internal reflection

are correct?


5 - 26

P - is more than the critical angle of glass

Q - The speed of light in the glass is higher than

in air

R - The refractive index of glass is greater than

air

A P and Q

B P and R

C Q and R

D P,Q and R

6 The diagram shows a semi-circular plastic block

is placed in a liquid.

Which of the following is correct?

A Density of the plastic block is less than

density of the liquid

B Refractive index of the plastic block is

less than refractive index of the liquid

C Critical angle of the plastic block is less

than critical of the liquid

D Angle of incidence is less than critical

angle of the liquid

7 The diagram shows a ray of light passing through

medium M to medium N.

Which of the following is correct?

A The angle of reflection is 55o

B The critical angle of medium M less than 35o

C Density of medium M less than the density

of medium N

8 The figure shows a ray of light PO traveling in a

liquid strikes the liquid-air boundary.

[ The critical angle of the liquid = 45o ]

In which direction does the light move from ?

A OQ

B OR

C OS

D OT

9 A ray of light incident on one side of a

rectangular glass block. If the angle of refraction

in the glass block is 40o ,

which one of the following diagrams best

represents this ray?

[ The critical angle of glass is 42o ]

10 The diagram shows a light ray, P, directed into a

glass block. The critical angle of the glass is 42o.

In which direction does the light move from point

Q?


5 - 27

11 The diagram shows a light ray , M, directed into a

glass block. The critical angle of the glass is 42o.

In which diagram does the light move from point

O ?

12 The figure shows a ray of light is incident in air

to the surface of Prism A and B.

Which comparison is correct ?

A Density of prism A < density of prism

B

B Critical angle of prism A < critical angle of

prism B

C Refractive index of prism A < refractive

index of prism B

13 The critical angle is

A the smallest angle of incidence in optically

more dense medium

B the smallest angle of incidence in optically

less dense medium

C the greatest angle of incidence in optically

more dense medium

D the greatest angle of incidence in optically

less dense medium

14 Which of the following shows the correct critical

angle , c of the semi- circular glass block ?

15 The diagram shows a light ray travelling from air

into a plastic block with an angle of incidence ,X.

What is the critical angle of the plastic?

16 The diagram shows a light ray travelling from air

into a glass prism.

What is the critical angle of the glass?


5 - 28

A 40o B 50

o

C 60o D 70

o

E 80o

17 The refractive index of water is 1.33.

What is the critical angle of the water.

A 44.5o B 46.9o

C 48.8o D 49.2o

E 54.3o

18 The refractive index of plastic block is 13 .

5

What is the value of the cosine of the critical

angle of the plastic?

A 5 B 12

12 13

C 13 D 5

12 13

E 13

5

19 The figure shows a ray of light AO traveling in

medium X strikes the medium X-air boundary.

[ The refractive index of medium X = 1.12 ]

In which direction does the light move from O ?

A OE B OD

C OC D OB

20 Which of the following not applies the principle

of total internal reflection?

A Prism binocular

B Mirror periscope

C Optical fibre

D Road mirage

21 The diagram shows a cross- section of a fibre

optic cable.

Which comparison is correct ?

A Density of P < density of Q

B Density of P >density of Q

C Density of P = density of Q

Answer:

1 A 11 C

2 D 12 B

3 D 13 C

4 D 14 C

5 B 15 D

6 C 16 B

7 B 17 C

8 D 18 D

9 A 19 C

10 C 20 A


5 - 29

Section A

(Paper 2)

Structure Question:

1. Diagram 1 shows a cross-sectional area of an

optical fibre which consist of two layers of glass

with different refractive index. The glass which

forms the inner core, Y is surrounded by another

type of glass which forms the outer layer, X.

(a) (i) Name the light phenomenon observed in

optical fibre?

Total internal reflection

[ 1 mark ]

(ii) Compare the refractive index of outer

layer X and inner core Y.

The refractive index of Y is higher than

the refractive index of X// Vice versa

[ 1 mark ]

(b) The refractive index of inner core Y is 2.10.

Calculate the critical angle of the inner core

Y.

Sin c = n

1 =

1.2

1= 0.4762

c = 28.44o // 28

0 26’

[2 marks]

(c) Name other optical device that applies the

phenomenon in (a)(i).

[ 1 mark ]

Prism periscope // prism binoculars // camera//

endoscope and etc.

2. Figure 4 shows a traveller driving a car on a hot

day. The traveller sees a

puddle of water on the road a short distance ahead

of him.

Puddle of water

Figure 4

a) Which part of the air is denser?

Close to the sky / cool air

…………………………………………………………

( 1 mark )

b) Name a phenomena of light that always depends

on the air density when light travels from the sky to

the earth before it reaches point X.

Refraction

…………………………………………………………

( 1 mark )

c) i) What is the phenomenon occurring at point X

Total internal reflection

……………………………………………………..…

(1 mark )

ii) What is the puddle of water actually?

The image of sky

…………………………………………………………

( 1 mark )

DIAGRAM 1


5 - 30

d) Using the diagram above, explain how the traveller

can see the puddle of

water on the road.

1.Light from sky to the earth refracted

2. The light reach at a point X, total internal

reflection occurred

…………………………………………………………

( 2 marks )

e) Name one optical instrument that uses the

phenomenon in (d)

Optical fibre

…………………………………………………………

( 1 mark )

3. Completing the ray diagram below, to show how a

periscope works: (critical angle of glass = 42o)

Answer:

[2 ma

Eye

e

Glass

prism object

tctct

Eye

Glass prism Object

45o Total internal

reflection takes

place because

angle of incident >

critical angle


5 - 31

U N D E R S T A N D I N G L E N S E S

Introduction

Lenses are made of transparent material such as glass or clear plastics.

They have two faces, of which at least one is curved.

Types of lenses (a) Convex lens, also known as converging

lens.

It is thicker at the centre of the lens.

(b) Concave lens, also known as diverging

lens.

It is thinner at the centre of the lens.

State the

differences

between convex

lens and concave

lens

Convex lens

When light ray which are parallel and close to

the principle axis strikes on a convex lens, they

are refracted and converge to a point, F on the

principle axis. This point is a focal point of the

convex lens.

Concave lens

When light rays are parallel to the principle

axis fall on a concave lens., they are refracted

and appear to diverge from the focal point on

the principle axis.

Common

terminology of

reflection of light

on a curved mirror

1. The focal point, F is a point on the principle axis where all rays are close and parallel to the

axis that converge to it after passing through a convex lens, or appear to diverge from it after

passing through a concave lens.

2. The focal length, f is the distance between the focal point and the optical centre.

3. The optical centre, C is the geometric centre of the lens. It is the point through which light

rays pass through without deviation.

4. The principle axis is the line passing through the optical centre, C.

5.4


5 - 32

Construction rules

of convex lens

Rule 1:

A ray parallel to the principle axis is

refracted through the focal point, f.

Rule 2:

A ray passing through the focal point is

refracted parallel to the principle axis.

Rule 3:

A ray passing through the optical

centre, C travels straight without

bending.

The point of intersection is the position

of the image.

The images formed by a convex lens

depend on the object distance, u.

Images form by

convex lens


cases shown below:

u = object distance; v = image distance ; f = focal length

Note: Point of intersection in the position of the image


image:

1.virtual

2.upright

3.magnified

4.Same side as the

object

Application:

1.magnifying glass

spectacle

2.lens for long-

sightedness.

B u = f ( Object, O is at F ) Characteristics of

image:

1.virtual

2.upright

3.magnified

4. Same side as the

object

Application:

1. to produce a

parallel a parallel

beam of light , as in a

spotlight,

astronomical

telescope


5 - 33

C f < u < 2f or f < u < r ( Object O is

between F and C

Characteristics of

image:

1.real

2.inverted

3.magnified

4. On apposite side

of the object.

Application:

1.projector lens

2.photograph

3. enlarger

4.objective lens of

microscope

D u = 2f or u = r ( Object ,O is at C) Characteristics of

image:

1.real

2.inverted

3.same size as the

object

4. On the opposite

side of the object

Application:

1.photocopying

machine

Eu > 2f or u > r ( Object, O is beyond C ) Characteristics of

image:

1.real

2.inverted

3.magnified

Application:

1.magnifying mirror

2.sharing mirror

3. make-up mirror

F u = ( Object ,O very far from the lens) Characteristics of

image:

1.virtual

2.upright

3.magnified

Application:

1.magnifying mirror

2.sharing mirror

3. make-up mirror


5 - 34

Construction rules

of concave lens

Ray 1:

A ray parallel to the principle axis is refracted

as if it appears coming from the focal point, F

which is located at the same side of the

incident ray.

Ray 2:

A ray passing through the focal point is

refracted parallel to the principle axis.

Ray 3:

A ray passing through the optical centre, C

travels straight without bending.

The point of intersection is the position of the

image .

The image formed by a concave lens are

always :

Virtual, upright and diminished.

Image formed by

convex mirror:


cases shown below:

u = object distance; v = image distance ; f = focal length


image:

1.diminished

2.virtual

3.upright

Application:

1. Blind Conner

mirror

2.Wide side view

mirror

(B ) f<u <2f (object at between f and 2f) Characteristics of

image:

1.diminished

2.virtual

3.upright

Application:

1. Blind Conner

mirror

2.Wide side view

mirror

1

2

3


5 - 35

Power of lenses Power of a lens = 1 .

Focal length

or P = 1 @ P = 100

f f( cm)

The unit of power of a lens is

Dioptre (D) or m-1

Convex lens : the power is taken to be

positive

Concave lens : the power is taken to be

negative

f = focal length

Linear Magnification (m) :

The linear

magnification , m

define as:

Where

f = focal length

u = object distance

v = image distance

m = linear magnification

ho = object height

hi = image height

Lens Formula

Sign Conventions

Type of lenses Convex lens Concave lens

Object distance ,u Always +

Object is always placed to the

left of the lens

Always +

Object is always placed to the

left of the lens

Image distance, v + if the image is real ( image

is formed on the right side of

the lens.

- if the image is virtual

( image is formed on the left

side of the lens).

+ if the image is real ( image

is formed on the right side of

the lens

- if the image is virtual

( image is formed on the left

side of the lens).

Focal length, f Always + Always -

Power of length, P Always + Always -

Linear magnification, m Size of image

I m I = 1 Image and object are the same size

I m I > 1 Enlarged image

I m I < 1 Diminished image


5 - 36

Meaning of real

image and virtual

image

A real imge is one which can be cast on a

screen.

A virtual imge is one which cannot be cast on a

screen.

Check Yourself:

Objective Question:

1 The image produced by a lens is caused by the

A total internal reflaction of ray

B diffraction of ray

C refraction of ray

D reflection of ray

2 The diagram shows parallel rays of light is

incident to a combination of plastics with

different refractive index.

Which of the following diagrams is correct?

3 The diagram shows parallel rays of light passing

through a liquid in glass container.

[ The refractive index of the liquid = 1.35 ]

Which of the following diagrams is true?

4 Which of the following drawing is not correct

path of the light rays?

5 Which of the following is true?

A The unit of the power of lens is Watt

B The power of a convex lens is negative

C A lens with a shorter focal length has a

lower power

D The rays of light passes through the optical

centre of lens without any refraction


5 - 37

6 Diagram shows light rays passing through a

convex lens .

What is the distance P ?

A Image distance

B Object distance

C Focal length

D Optical length

7 The diagram shows the action of a magnifying

glass.

Which point is the principal focus of the lens?

8 The diagram shows an image ,I is formed by a

convex lens.

Where is the position of the object?

9 The diagram shows an image ,I is formed by a

concave lens.

Where is the position of the object?

10 Figure shows four light rays A,B,C and D passing

through a convex lens. F is the focal point of the

length. Which of the following path of the light

rays is not correct?

11 What is the power of a convex lens which has a

focal length 50 cm ?

A -0.2 D B 0.2 D

C -2.0 D D 2.0 D

E 4.0 D

12 The power of a lens is - 40 D. What is the type

of the lens and its focal length?

Type of length Focal length

A Concave lens -2.5 x 102 m

B Concave lens -2.5 x 10-2

m

C Convex lens -2.5 x 102 m

D Convex lens -2.5 x 10-2

m

E Concave lens -4.0 x 10-2

m

13 A convex lens of focal length ,f. The lens

produces a enlarged , virtual and upright

image.The object distance is

A less than f

B between f and 2f

C same as 2f

D more than 2f

14 A light bulb is placed at the principal focus of a

convex lens. After travelling through the lens the

rays of light is

A parallel

B converge

C diverge


5 - 38

15 The focal length of a convex lens is f . Which of

the following object distances , u will produced

an inverted image ?

A u < f B u >f

C f < u < 2f D u > 2f

16 The diagram shows an object which is placed at u

cm from centre of a convex lens. The focal length

of the lens is 20 cm.

Which of the following characteristics of the

image is not correct when u is 10 cm ,15 cm , 35

cm and 45 cm from the lens?

u / cm Characteristics of the image

A 10 Virtual and bigger

B 15 Virtual and bigger

C 35 Real and smaller

D 45 Real and smaller

17 An object is placed 25 cm in front of a convex

lens and its image is formed at infinity. If the

object is placed 20 cm in front of the lens , the

image is

A inverted

B smaller than object

C formed on the same side as the object

18 The diagram shows an object ,O is placed in front

of a convex lens produced an image , I.

Which of the following is not true?

A The focal length of the lens is 60 cm

B The linear magnification is 1

C The image I is a real image

19 A convex lens of focal length 20.0 cm is turned

to face a distant object. The position of the screen

is adjusted until a sharp inverted image is formed

on the screen.

What is the distance of the screen from the lens ?

A 15.0 cm B 20.0 cm

C 25.0 cm D 40.0 cm

E 50.0 cm

20 The characteristics image is produced by a

concave lens is

A magnified,virtual,upright

B diminished,virtual,upright

C magnified,real,inverted

D diminished,real,inverted

21 An object is placed at 18.0 cm from a convex

lens of focal length 20.0 cm.

What is the the characteristics of image ?

A virtual, upright and magnified

B real, inverted and magnified

C virtual ,upright and diminished

D real, inverted and diminished

22 A lens is placed between a light bulb and a

secreen. The distance between the light bulb and

screen is 60.0 cm. The position of the lens is

adjusted until the size of the image is same as the

size of the object.

What is the type and the focal lenghth of the

lens?

Type of lens Focal length

A Convex lens 30 cm

B Convex lens 15 cm

C Concave lens 30 cm

D Concave lens 15 cm


5 - 39

23 An object is placed at a distance 10 cm in front of

a convex lens of power 5D.

What is the image distance and the characteristic

of the image?

Image distance Characteristic of the image

A 10.0 cm Virtual image

B 10.0 cm Real image

C 20.0 cm Virtual image

D 20.0 cm Real image

24 An object is placed at a distance 80 cm in front of

a concave lens of focal length 20 cm.

What is the image distance and the characteristic

of the image?

Image distance Characteristic of the image

A 16.0 cm same side of the lens as the

object

B 16.0 cm the other side of the lens as

the object

C 26.7 cm same side of the lens as the

object

D 26.7 cm the other side of the lens as

the object

25 The diagram shows an image I of an object O is

formed by a convex lens.

What is the linear magnification of the image?

A 0.5 B 1.0

C 3.0 D 4.0

E 5.0

26 An object is placed at a distance30 cm from a

convex lens with a focal length of 25.0 cm.

What is the linear magnification ?

A 2 B 3

C 4 D 5

E 6

27 A convex lens with a focal length of 20.0 cm to

form an image which is 2 times the size of the

object. What is the object distance ?

A 10.0 cm B 15.0 cm

C 30.0 cm D 40.0 cm

E 60.0 cm

28 An object of height 5 cm is placed at 15 cm

from a convex lens of focal length 10.0 cm.

What is the image height ?

A 5 cm B 10 cm

C 15 cm D 20 cm

E 25 cm

29 An object of height 6.0 cm is placed at 8 cm

from a convex lens of power 50 D.

What is the image height?

A 2 cm B 4 cm

C 5 cm D 6 cm

E 8 cm

30 A convex lens is used to produce a real,

magnified and inverted image. What is the effect

on the image produced when the upper portion of

the lens is covered by a coin ?

A The upright image is formed

B The size of the image is reduced

C The brightness of the image is

reduced

31 The diagram shows a graph of object distance,u

against image distance ,v of the lens.

What is the focal length of the lens?

A 5 cm B 10 cm

C 20 cm D 40 cm

E 80 cm


5 - 40

32 The diagram shows a graph of image distance,v

against linear magnification ,m of the lens.

What is the focal length of the lens?

A 14.0 cm B 15.0 cm

C 16.0 cm D 17.0 cm

E 18.0 cm

Answer:

1 C 11 D

2 D 12 B

3 C 13 A

4 B 14 B

5 D 15 A

6 C 16 D

7 D 17 A

8 C 18 A

9 D 19 D

10 D 20 B

Section A

(Paper 2)

Structure Question:

1 The Figure shows an image of letters FIZI when

viewed through a glass of water.

(a) State the light phenomenon that causes the

image FIZIK to be enlarged.

Refraction of light

………………………………………………

(1 mark)

(b) What is the change size of the image if the

water is replaced with a transparent liquid of

a greater density?

Size of image increases/bigger

………………………………………………

(1 mark)

(c) The glass of water is replaced with a lens M

with focal length of 10 cm. The distance

between the book cover and the centre of the

lens is 8 cm.

It is observed that the image FIZIK is

enlarged.

(i) Name the type of lens M.

Convex lens

…………………………………………

(1 mark)

(ii) Calculate the distance of the image from

lens M.

1 = 1 + 1

f u v

1 = 1 + 1

10 8 v

v = -40 cm

2 The diagram shows an object is placed in front of

a convex of focal length 15.0 cm.

(a) (i) Complete the ray diagram in the

diagram above to show the formation

of the final image.

(3 marks)


5 - 41

(ii) State the characteristics of the image.

Inverted, real and magnified

............................................................

(2 marks)

(b) Determine the linear magnification

m= v = 65 = 2.75

u 20

(2 marks)

(c) The object height is 2.5 cm,calculate the

image height. (2 marks)

m = hi

ho

2.75 = hi

2.5

hi = 6.9 cm

(d) What will happen to the characteristis of the

image when

(i) the convex lens is replaced by a

concave lens of focal length 15.0 cm.

Virtual, upright and diminised

............................................................

(2 marks)

(ii) the object is placed at the ”10 cm ”

mark.

Virtual, upright and magnified

............................................................

(2 marks)

3 When an object is placed 40 cm from a convex

lens ,the image formed is of the same size as the

object.

(a) Determine,

(i) the focal length of the lens

(1 mark)

f = 20 cm

(ii) the power of the lens

P = 5D

(1 mark)

(b) If the object is now placed in front of the

lens, an image which is 4 times the size of

the object is formed.

(i) Calculate the object distance.

(2 marks)

m= v , 4 = 40 , u = 10 cm

u u

(ii) State the characteristics of the image.

(2 marks)

Magnified, virtual and upright

.................................................

(c) State the light phenomenon that causes the

image is formed by the lens?

( 1 mark)

Refraction of light

...................................................................

(d) What is the effect on the image produced

when the lower portion of the lens is covered

by a card? (1 mark)

The size of image reduced/become smaller

................................................................


5 - 42

T H E U S E S O F L E N S E S I N O P T I C A L D E V I C E S

Introduction There are many types of optical devices used lenses such as magnifying glass, microscope,

telescope, camera and slide projector etc. For every types of the devices we must learn about the

uses of the instruments, lens characteristics is used, normal adjustment of the instruments , ray

diagrams and the characteristics of the final image which are formed .

1. Compound Microscope

Give the use of a

compound

microscope.

A microscope is used to observe and magnify tiny objects such as bacteria.

Draw a diagram to

describe the

formation of

image formed by

microscope.

1. It consist of two powerful convex lenses of short focal length (5.0 cm-10.0 cm)

2. The lens which receives light rays from the objects is called the objective lens. The lens which

is used for viewing the final image is called the eyepiece lens.

3. The focal length of the objective lens is fo whereas the focal length of the eyepiece lens is fe.

4. The object is placed at a distance between fe and 2fe so that the imaged formed is inverted,

magnified and real in front of the eyepiece lens.

5. The position of the eyepiece lens is adjusted until the position of the first image is less than fo

from the eyepiece lens.

Define the

characteristics of

the image formed

by objective lens o

microscope.

The final image formed is inverted, magnified and virtual.

5.5


5 - 43

2. Magnifying glass

Give the use of a

compound

microscope.


Draw a diagram to

describe the

formation of

image formed by

microscope.

1. It consists of two powerful convex lenses of short focal lengths .

2. An object is placed at a position less than the focal length of the lens.

3. The magnifying power increases if the focal length of the lens is shorter.

4. A shaper and larger image is seen at the near point of the eye. In general, the near point is

taken as 25 cm.

Define the

characteristics of

the image formed

by objective lens o

microscope.

The image formed is magnified, upright and virtual.

3. Astronomical Telescope

Give the use of a

compound

microscope.


Draw a diagram to

describe the

formation of

image formed by

microscope.


5 - 44

1. It consist of an objective lens and eyepiece lens.

2. The objective lens is used to receive light rays from distant object.

3. The first image formed is at focal point of the objective lens Fo. It is real, inverted and

diminished.

4. The first image now becomes the object for the eyepiece lens.

5. The eyepiece lens is adjusted so that the first image is situated at the focal point of the

eyepiece lens , Fe.

6. The telescope is said to be in normal adjustment.

7. For normal adjustment of the telescope, the separation between the two lenses is fo + fe.

Define the

characteristics of

the image formed

by objective lens o

microscope.

The first image formed is at focal point of the objective lens Fo.It is real, inverted and

diminised.

The final image formed is at infinity.

4. Slide Projector

What is the

function of each

component of a

slide projector?

Component Functions

Slide Acts as an object

Projector Lens The lens has to be placed far away from the

screen in order to get a large image.

Condenser Lens Acts as a heat filter to protect slide from

getting over heated.

Draw a diagram to

describe the

formation of

image formed by

microscope.

1. It uses a convex lens to form a real, inverted and magnified image of the slide or film on a

screen.

2. The slide being the object is placed between f and 2f from the projector lens

The lamp is placed at the focal point of the concave mirror to reflect all light from the lamp

back to the condenser.

3. The movable projector lens focuses a sharp, inverted and magnified image onto a screen.

4. The slide should be placed upside-down(inverted) in order to form an upright image on the

screen.


5 - 45

Define the

characteristics of

the image formed

by objective lens

of microscope.

Upright, real , magnified

5. Camera

Draw a diagram to

describe the

formation of

image formed by

microscope.

State the parts in a

camera and their

functions?

1. The convex lens is used to produce a real, inverted and diminished image on a light sensitive

film at the camera.

2. The diaphragm is used to adjust the size of the exposure time when taking photographs.

3. The shutter speed is used to control the exposure time when taking photographs.

Check Yourself:

Objective Question:

1 Which of the following combinations is the

characteristics of a magnifying lens ?

Object distance/cm Focal length/ cm

A 5 10

B 8 5

C 10 5

D 20 8

2 A convex lens is used as a magnifying glass.

What are the characteristics of the image?

A magnified,upright,virtual

B magnified,upright,real

C magnified,inverted,virtual

D magnified,inverted,real

3 Which of the following is true about the eyepiece

of a microscope?

A Consist of a concave lens which has lower

power than the objective lens.

B Consist of a convex lens which has lower


C Consist of a concave lens which has higher


D Consist of a convex lens which has higher



5 - 46

4 Which of the following is true concerning the

operation of a compound microscope?

A The focal length of objective lens greater

than the focal length of eyepiece

B Both objective lens and eyepiece has a high

power.

C The characteristics of final image are

magnified, upright and virtual

5 The characteristics of image is formed by the

objective lens of a microscope are

A virtual,diminished,upright

B real,magnified,inverted

C virtual,magnified,inverted

D real,magnified,upright

6 Which of the following statements about the

objective lens and eyepiece of a telescope?

Power of objective

lens

Power of

eyepiece

A low high

B high low

C low low

D high high

7 Two convex lens of power 2.5D and 20 D

respectively is used in a telescope. What is the

distance between the lens in normal adjustment?

A 8.0 cm B 17.5 cm

C 22.5 cm D 45.0 cm

E 50.0 cm

8 Two convex lens of focal length 100 cm and 5

cm respectively is used in a telescope. What is the

linear magnification of the telescope?

A 0.05 B 20

C 100 D 105

E 500

9 A telescope has two convex lens of power 4.0 D

and 20.0D respectively.

Which of the following is true?

Linear

magnification

Distance between the

lens /cm

A 5 24.0

B 5 30.0

C 4 30.0

D 4 24.0

E 0.2 16.0

10 The characteristics of final image in a telescope

are

A virtual,upright,magnified,located at the focal

point

B real,inverted,magnified,located at infiniti

C virtual ,inverted,magnified,located at infiniti

11 The characteristics of the image is formed by a

camera are

A virtual,upright ,enlarged

B real,inverted,diminished

C virtual,inverted,diminished

D real,upright,enlarged

12 The image is formed by a slide projector is

A enlarged,real,upright

B enlarged,real,inverted

C diminished,virtual,upright

D diminished,real,inverted

13 Which of the following optical instrument

produced real image?

A Telescope B Magnifying glass

C Microscope D Slide projector


5 - 47

Answer:

1 A 11 B

2 A 12 A

3 D 13 D

4 B 14

5 B 15

6 A 16

7 D 17

8 B 18

9 B 19

10 C 20

Section A

(Paper 2)

Structure Question:

1 The diagram shows the arrangement of the lenses

in a compound microscope.

(a) Complete the ray diagram in the diagram

above.

Answer:

(b) State the characteristics of the final image

formed.

(1 mark)

Inverted, virtual and magnified

..................................................................

(c) State two differences between telescope and

microscope by completing the table below.

Telescope Microscope

fo > fe

fe > fo

Final image , virtual

image at infinity

Final image , virtual

image, inverted ,

magnified

2 The diagram shows the arrangement of the lenses

in a telescope. The power of lens A and lens B are

0.5 D and 5D respectively.

(a) Why do the light rays PQ and RS are

parallel? (1 mark)

Because the object is from infinity

………………………………………….

(b) State the focal length of

(i) lens A (2 marks)

P = 1 , fo= 1 = 2.0 cm

fo 0.5

(ii) lens B (2 marks)

P = 1 , fe= 1 = 0.2 cm

fe 5

(c) What is the distance between lens A and lens

B? (2marks)

fo + fe = 2.0 + 0.2

= 2.2 m


5 - 48

(d) What is the linear magnification of the

telescope? (2 marks)

m = fo, = 2.0 = 10

fe 0.2

(e) In the diagram above , complete the ray

diagram of the telescope. (3 marks)

(f) State the characteristics of the final image

formed. (2 marks)

Virtual , formed at infinity, inverted

...................................................................

3 The figure shows the lens and mirror arrangement

for a slide projector.

(a) What is the function of

(i) concave mirror (1 mark)

Reflects light to the condenser

..........................................................

(ii) condenser lens (1 mark)

Acts as a heat filter to protect

slide from getting overheated.

..........................................................

(b) State two normal adjustment should be done

while using the slide projector.(2 marks)

1. The slide being the object is placed

between f and 2f from the projector lens .

..................................................................

2. The slide should be placed up side-down in

order to form an image on the upright screen.

………………………………………………

(c) State the characteristics of the final image

formed.. (2 marks)

Real, magnified and upright

..................................................................

[ 2 marks ]

[2 ma

Form 4 Physics Chapter 5

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