1. Describe two differences between electromagnetic waves and other (mechanical) waves.

2. Write down the names of all seven types of electromagnetic waves in order of increasing frequency.

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

Curved Mirrors, Ray Diagrams and Nature of Image

Question:How do we “see” things?

Mirror

Normal

?

Mirror

Brick Wall

Mr. X

A B C D

Plane Mirrors

Light from object reflects

into eye

Eye sees image back here

Image is virtual and laterally

inverted

ATOYOT

The two types of curved mirrors:

1. Concave (Converging) Mirror

2. Convex (Diverging) Mirror

Concave (Converging) Mirrors

Concave (Converging) Mirrors

Concave Mirrors• Concave (or converging) mirrors focus light

at the focal point.

F

Convex (Diverging) Mirrors

Convex (Diverging) Mirrors

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

Ray Diagrams

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

The two important rules:1. Parallel to pa → Focal point2. Focal point → Parallel to pa(pa = principal axis, the horizontal line)

Concave (Converging) MirrorSize Orientation Nature

Behind C

At C

Between C & F

At F

Between F & P

1. 2. 3.

4. 5.

Concave (Converging) MirrorSize Orientation Nature

Behind C Diminished Inverted Real

At C Same Inverted Real

Between C & F Enlarged Inverted Real

At F No image No image No image

Between F & P Enlarged Upright Virtual

Convex (Diverging) MirrorSize Orientation Nature

Behind C

At C

Between C & F

At F

Between F & P

Convex (Diverging) MirrorSize Orientation Nature

Behind C Diminished Upright Virtual

At C Diminished Upright Virtual

Between C & F Diminished Upright Virtual

At F Diminished Upright Virtual

Between F & P Diminished Upright Virtual

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.

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.

Mirror Formulae ONE

• Descartes’ Formula:

• and:

• m = magnification factor• h = height• d = distance from mirror

oi ddf111

o

i

o

i

dd

hhm

• f is + if the mirror is concave

• f is − if the mirror is convex

• di is + if the image is in front of the mirror

• di is − if the image is behind the mirror

• hi is + if the image is upright/virtual

• hi is − if the image is inverted/real

• m > 1 if the image is enlarged

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:

• and:

• S = distance from focal point• All distances are positive but care must be

taken when calculating Si or So

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. Activity 5B