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
