KCL Section 4: Reflection and refraction(Waves and photons)

Question 1

What is the normal?

Answer 1

The normal is an imaginary line drawn perpendicular to the point where the ray hits a boundary between media.

Question 2

What is the refractive index?

Answer 2

The refractive index is a ratio which tells you how much the speed of light will change (and therefore how much light will change direction) when it arrives at a boundary between two mediums.

Question 3

What is the refractive index formula?

Answer 3

Refractive index from medium 1 to medium 2 = speed in medium 1 / speed in medium 2

Question 4

The speed of light in a certain glass is 1.8 x 108 ms-1. What is the refractive index of the glass?

Answer 4

1.7

Question 5

The speed of light in air is 2.9979 x 108 ms-1. What is the refractive index of the air?

Answer 5

1.00

Question 6

The speed of light in a certain plastic is 2.08 x 108 ms-1. What is the refractive index of the plastic?

Answer 6

1.44

Question 7

The speed of light in a different plastic is 1.92 x 108 ms-1. What is the refractive index of the plastic?

Answer 7

1.56

Question 8

The speed of light in water at 25oC is 2.26 x 108 ms-1. What is the refractive index of the water?

Answer 8

1.33

Question 9

The refractive index of diamond is 2.4. What is the speed of light in diamond?

Answer 9

1.3 x 108 ms-1

Question 10

The refractive index of an oil is 1.518. What is the speed of light in the oil?

Answer 10

1.98 x 108 ms-1

Question 11

The refractive index of hexane is 1.37. What is the speed of light in hexane?

Answer 11

2.19 x 108 ms-1

Question 12

What is Snell’s law?

Answer 12

n1sinθ1= n2sinθ2 (where refractive index is n = c/v)

Question 13

What is the angle of refraction when a light ray passes from water (n1 = 1.33) into glass (n2 = 1.50), hitting the interface between the two at an angle of 48° to the normal?

Answer 13

41.2

Question 14

The speed of light is 3.0 x 108m s’ in air. 2.3 x 10”m s 1 in water and 2.0 x 10”m s-1 in glass.
Calculate the angles Q and for light incident at 40° to the normal at the air-water interface in Figure 15.9.

Answer 14

Air to water = 1.3
Air to glass = 1.5
Water to glass = 1.2

Question 15

Define refraction

Answer 15

Refraction is a change in wave speed when the wave moves from one medium to another. There is a corresponding change in wave direction, governed by Snell’s law.

Question 16

Define refractive index

Answer 16

Refractive index, n, can be defined in several ways, but it is fundamentally a result of the change in wave speed

Question 17

Define Snell’s law

Answer 17

The values of n1 and n2 are the refractive indices in each medium, and the values of 01 and 02 are the angles that the ray makes to the normal to the interface between the two media, at the point the ray meets that interface.

Question 18

175

Answer 18

175