Chapter 2: Reflection of Light

Question 1

What are the 2 laws which govern reflection of light at any interface?

Answer 1

1. The incident ray, reflected ray and normal to reflecting surface all lie in the same plane
2. Angle of incidence, i, equals the angle of reflection, r.

Question 2

Why would a perfect reflecting surface be invisible?

Answer 2

when parallel light encounters an irregular surface it is scattered in many directions (diffuse relfection0

this is how most objects (that aren’t self-luminous) are seen

Question 3

What are the 5 properties of the images of objects formed by reflection at a plane surface (e.g. flat mirror)?

Answer 3

1. virtual
2. erect
3. laterally inverted
4. lie along line perpendicular to the reflecting surface
5. are as far behind the surface as the object is in front of it

Question 4

What happens to the reflected ray from a mirror if the plane mirror is rotated?

Answer 4

the reflected ray is deviated through an angle twice the angle of rotation of the mirror

Question 5

What are the 4 key features of concave and convex mirrors to be aware of when drawing ray diagrams?

Answer 5

1. centre of curvature, C, is centre of sphere of which the mirror is a part
2. pole of the mirror, P, is centre of the reflecting surface
3. Principle focus, F is where rays parallel to the principal axis are reflected towards (concave) or away from (convex)
4. CP is twice the length of FP

Question 6

Are the images formed from spherical mirrors (concave + convex) real or virtual?

Answer 6

• concave = real
• convex = vrtual

Question 7

What are the 2 rays you need to construct when determining the image from a spherical mirror?

Answer 7

1. line from top of object that is paralell to the principal axis, and is reflected to or away from F
2. line from top of object that goes straight through C and is reflected back in the same direction

Question 8

What + where will the image be for a concave mirror + object outside the centre of curvature, C?

Answer 8

real, inverted, diminished, between C and F

Question 9

What + where will the image be for a concave mirror + object between the centre of curvature, C and principal focus, F?

Answer 9

real, inverted, enlarged, lying outside centre of curvature C

Question 10

What + where will the image be for a concave mirror + object inside the principal focus, F?

Answer 10

erect, virtual, enlarged (rays travelling away from the mirror are diverging, but convergent on the other side therefore virtual image)

Question 11

What + where will the image be for a convex mirror at any distance from the mirror?

Answer 11

virtual, erect, diminished

Question 12

How can you calculate the position of the image formed by a spherical mirror?

Answer 12

you need the focal length and the distance of the object from the mirror:

1/v - 1/u = 1/f (or 2/r)

where v = distance of image from mirror, u = distance of object from mirror, f= focal length, r= radius of curvature

Question 13

How can you calculate magnification of a spherical mirror?

Answer 13

i/o = -v/u

i=image size, o=object size, v=distance of image from mirror, u=distance of object from mirror