Chapter 7&8- Reflection And Refraction

Question 1

Properties of plane mirror images

Answer 1

1) Virtual (image is formed by imaginary light rays and cannot be formed on a screen)
2) Upright
3) the same size as the object
4) same distance behind the mirror as the object is in front of the mirror
5) laterally-inverted

Question 2

Define refraction

Answer 2

Refraction can be described as the bending of light when it passes from one medium to another

Question 3

Why does light bend?

Answer 3

Light bends when it enters another medium because the speed of light changes when it enters another medium.

Question 4

Refractive index

Answer 4

The refractive index (n) of a medium may be defined as the ratio of the speed of light in vacuum (c) to the speed of light in that medium (v)

Hence, n=c/v

Question 5

When a ray of light travels from a medium of lower refractive index to a medium of higher refractive index…

Answer 5

It bends towards the normal

Question 6

Speed of light in vacuum

Answer 6

3 x 10^8 m/s

Question 7

Angle of deviation

Answer 7

Angle of deviation of alight Ray is defined as the angle between the angle of its incident direction and its refracted direction

Question 8

Laws of refraction

Answer 8

• the incident ray, refracted Ray and normal at point of incidence all lie on the same plane
• the ratio of the sine of the incident angle to the sine of the angle of refraction is a constant

Question 9

Snell’s law

Answer 9

n=sin i/sin r ; n1sin01=n2sin02

Ratio of the sine of the incident angle to the sine of the angle of refraction is a constant

Question 10

State the principle of reversibility

Answer 10

A light Ray will travel along the same path regardless of the direction it started from

Question 11

Partial reflections

Answer 11

Whenever a light Ray reaches a surface and refracts, part of the light will be partially reflected. Only some of the light energy successfully passes into the other medium, therefore some of the light energy is always reflected

Question 12

Define critical angle

Answer 12

n=1/sin c

The critical angle is defined as the angle of incidence in the medium with higher refractive index for which the angle of refraction in the medium with lower refractive index is 90 degrees

Question 13

Total internal reflection

Answer 13

When the angle of incidence is increased beyond the critical angle, refraction can no longer occur, because r cannot increase to more than 90 degrees. Instead, total internal reflection occurs, where all the light is reflected back into the object according to the laws of reflection

Question 14

Conditions for total internal reflection to occur

Answer 14

1) light Ray must travel from a material with higher refractive index towards a material with lower refractive index
2) the angle of incidence of the light ray must be greater than the critical angle of the medium

Question 15

State the laws of reflection

Answer 15

• The incident Ray, reflected Ray and normal at point of incidence all lie on the same plane
• The angle of incidence is equal to the angle of reflection