Grade 10 Light

Light

K Warne

SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY

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Light Rays Give evidence to show that light travels in straight lines

• Draw ray diagrams to represent the way in which light travels.

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Reflection of Light

• Light is reflected

(bounced) off

surfaces.





Vision

• Objects are seen when

light reflects off them

into our eyes.





Every day Refraction

Refraction is seen in a

number of everyday

circumstances.

• Water mirage on

roads.

• Distortion of

images viewed

through a glass

prism.

• Distortion of

objects viewed in

water.





Passage of light through a glass block

A

B

AB is the incident ray.

The emerging ray is parallel to the

incident ray if the block is a rectangle.

Indicate incident rays

Indicate incident angles and

refracted angles on your

diagram.

i

r

Angle of incidence

Angle of refraction

Refracted ray

Emergent ray






On entering the glass (more

optically dense) block the light is

refracted TOWARDS the normal.

On exiting the glass (more

optically dense) block the

light is refracted AWAY from

the normal.

A

B


“i” is the incident angle i

rThe light ray is refracted

(bent) because :

• it enters a medium of

different optical density

• At an angle (not 90o)

BC is the REFRACTED

ray. “r” is the angle of

refraction.

C

D

CD is the

EMERGENT ray.





Refraction of waves

• Waves ……………

on entering a …….

………. medium.

• If the wave strikes

this medium at ….

……….. it then

changes ………….

Normal line

90° to the

surface

The wave bends …………………………….. on entering a

more dense medium at an angle.

The waves bend …………………………….. when exiting a

more dense medium.






On entering the glass (more

optically dense) block the light

is refracted TOWARDS the

normal.

On exiting the glass (more

optically dense) block the

light is refracted AWAY

from the normal.

A

B


“i” is the incident angle i

rThe light ray is refracted

(bent) because :

• it enters a medium of

different optical density

• At an angle (not 90o)

BC is the

REFRACTED ray.

“r” is the angle of

refraction.

C

D

CD is the

EMERGENT ray.





“Mirage” on Road

A “mirage” is simply an image of the sky that is

formed by the refraction of light through air of

varying densities due to temperature gradients.

Sky

Hot air

cold air

Light appears

to come from

road





Real and apparent depth

Objects viewed in

water………………

……………………

……………………

……………………

…In reality the

object is not seen at

all - only the image!

Draw in the light rays - to show the formation of the image.

Label the object, image, real depth and apparent depth.





Archer Fish• HW: Draw a ray diagram to show the refraction effects that must be taken into

account by an archer fish if it is to “shoot” down an insect outside the water

effectively.

• THE FISH MUST AIM LOWER THAN

• THE OBJECTAPPEARS! AIM





Real and apparent depth – HW 2

• Draw the

position of the

image.

• Show by means

of light rays why

the object

appears

shallower than it

is.





Total internal reflection





Optical Fibres

• The light in a fiber-optic cable travels through the core (hallway) by constantly

bouncing from the cladding (mirror-lined walls), a principle called total

internal reflection. Because the cladding does not absorb any light from the

core, the light wave can travel great distances.

• However, some of the light signal degrades within the fiber, mostly due to

impurities in the glass.





Triangular Prisim

ir

dN

i=angle of incidence

r=angle of refraction

d=angle of deviation





Converging Lenses

Parallel light rays

Parallel to principle axis

Parallel light rays

Refracted towards a

centre point – we say

they converge to a point.





Diverging Lenses





Ray Diagrams – Centre line

Principle axis

In a thin lens the displacement is negligible. The rays are drawn

as if refracting from the center line.

.F





Ray Diagrams - Optical Centre

Principle axis

Light rays passing along the

……………….. are ………

…………………… as they

strike both surfaces at 90°

Any ray

passing

through the

…………..

………….

can be

thought of as

passing

……………

…………….

In a thin lens the displacement is negligible.





Ray Diagrams -Focal Point

…………………….

… ....

F ……...

………..

•

Any ray striking the lens ………… to the principle axis is

refracted through the …………….. point.

These values are the ………… for either side of a ………...………… lens.

Parallel to ………………… ………..

…………….

…….•••





Diverging Lenses

F

F -…….

……….

……. …………..•

In a diverging lens the rays …………………. to have

originated at the ……………… point.





Ray Diagrams

• Three rays can be used to find the image of any lense.





Light PracticalPart I

Measure the angle of incidence when the angle of refraction is 90°

Part II

• Optical bench – measure: the distance from the object to the lens (Do ),

height of the object (Ho) and the distance from the image to the lens

(DI) and the height of the image (Ho ).

Write up method – and give a diagram!

RESULTS

Do (Ho) Di Hi (relative to Ho) .

1 >2F between 2F and F diminished (smaller)

2 At 2F

3 2F > x > F

4 At F

5 < F





Light Practical

ObjectImage

Do Di

HoHi

Do greater than 2F

Do equal to 2F

Do less than 2F

F= 50cm

Ray diagrams p 39





Light Practical

Object ImageDo Di

Ho

Object further than 2F

Image:

• Between F & 2F

• Inverted

• Real

• Diminished

F•

F•

2F•

2F•

HI

Magnification = = = 0.44Hi

Ho

1.9

4.3

Magnification = = = 0.5Di

Do

3.8

7.6

Do greater than 2F, Do equal to 2F, Do between 2F & F, Do equal to F, Do less than F





Compound Microscope

F•2F F F 2F





Eye - Defects

This is commonly

called short

sighted.

Object Far away

Distant objects

the lens is not

stretched

enough. (Too fat)

Rays are focused in

front of retina are

blurred.

Object close up are

focused clearly.

A diverging lens

would cause distant

rays to focus on the

retina and normal

sight is restored.

Short Sighted

Corrective glasses





From World Book © 2002 World Book, Inc., 233 N. Michigan Avenue, Suite 2000, Chicago, IL

60601. All rights reserved. World Book i llustrations by Charles Wellek

From World Book © 2002 World Book, Inc., 233 N. Michigan Avenue,

Suite 2000, Chicago, IL 60601. All rights reserved. Nikon, Inc.

Eye vs Camera

ENLARGE





Hi -

This is a SAMPLE presentation only.

My FULL presentations, which contain loads more slides (with all the gaps filled in) as well as

other resources, are freely available on my resource sharing website:

www.warnescience.net

(paste into your browser if link above does not work)

Have a look and enjoy!

Keith Warne






Grade 10 Light

Education

reflection of light

refraction of light

light travels

passage of light

light wave

rthe light ray

light signal

glass block