Write the names of the seven electromagnetic waves in the order of frequency (low to high)

1. Write the names of the seven electromagnetic waves in the order of frequency (low to high)

2. The frequency of an electromagnetic wave is measured to be 1.6 x 1018 Hz. What type of electromagnetic wave would it be?

3. The wavelength of microwave radiation produced by a microwave oven is 12.2 cm. Calculate the corresponding frequency.

ATOYOT

How do we “see” things?

Plane Mirrors

Light from object reflects

into eye

Eye sees image back here

Image is virtual and laterally

inverted

Convex (diverging) Mirrors

Concave (converging) Mirrors

Plane Mirrors

Light from object reflects

into eye

Eye sees image back here

Image is virtual and laterally

inverted

Concave Mirrors• Concave (or converging) mirrors focus light

at the focal point.

F

Convex Mirrors • Convex mirrors have a focal point behind

the mirror.• Convex (or diverging) mirrors spread the

light rays apart so that they appear to have come from the focal point

F

Plane (flat) Concave (converging)

Convex (diverging)

Enlarged or diminished

Inverted or upright

Real or virtual

Plane (flat) Concave (converging)

Convex (diverging)

Enlarged or diminished Neither Both Diminished

Inverted or upright Upright Both Upright

Real or virtual Virtual Both Virtual

Convex (diverging) mirrorsA convex mirror always produces virtual images which are always upright and smaller than the object. The image is formed behind the mirror, between the principal focus and the mirror.

Concave (converging) mirrorsThe image will be real, inverted if the object is located behind the principal focus.The image will be virtual, upright and enlarged if the object is located between the mirror and the principal focus.

P = pole , pa = principal axisC = centre of curvature r = radius of curvatureF = Focal point or focus f = focal lengthf = r / 2

C F P

rpa

f

Ray Diagrams• Rule 1: An incident ray parallel to the pa is

reflected back through the focal point.

F

Ray Diagrams• Rule 2: An incident ray that passes

through the focal point on the way to the mirror is reflected back parallel to the pa.

F

Ray Diagrams• Rule 3: An incident ray headed towards

the pole reflects back at an equal angle

F P

How to draw ray diagramsStep 1.mirror → pole → mirror line → Principal axis → principal focus (F) → object (arrow)Step 2.Draw a ray travelling horizontally from the top of the object towards the mirrorStep 3.If Concave = FocusIf Convex = Pole

Concave (converging) MirrorWhen the object is located behind the principal focus.

Concave (converging) MirrorWhen the object is located between the mirror and the principal focus.

Convex (diverging) mirrors

Draw these ray diagrams1. An object is standing in front of a

concave mirror, closely behind its focus.

2. An object is standing in front of a concave mirror, far behind its focus.

3. An object is standing between a concave mirror and its focus.

4. An object is standing in front of a convex mirror.

Mirror Formulae ONE• Descartes’ Formula:

• Or:

• m=magnification factor• h=height of image or object• d=distance from mirror to image or object• Distances behind the mirror are negative• hi is negative if the image is virtual

oi ddf111

o

i

o

i

dd

hhm

Using Descartes’ Formula – EXAMPLES

a) Find the position of the image located 40m in front of a concave mirror of radius of curvature 64m.

b) An object 7m high is placed 15m from a convex mirror of radius 45m.Find the position AND the height of the image.

• Newton’s Formula:

• Or:

• S=distance from focal point to image or object

• All distances are positive but care must be taken when calculating Si

or So. • It is usually necessary to sketch a ray

diagram to check.

2fSS oi

fS

Sf

hhm i

oo

i

Mirror Formulae TWO

Using Newton’s Formula – EXAMPLES

a) An object 7m high is placed 15m from a convex mirror of radius 45m.Find the position AND the height of the image.

b) An object 6m high is placed 30m in front of a convex mirror of focal length 40m. Find the position, nature and size of the image formed.

Finish these by this Thursday

1. Homework Booklet Worksheet TWO

2. NCEA 2004 & 2005

3. NCEA 2008

4. Activity 5B