Refraction Part A

Question 1

Speed of Light in (i)Air (ii)Water (iii)Glass

Answer 1

(i) 3 x 10⁸ ms^-1
(ii) 2.25 x 10⁸ ms^-1
(iii) 2 x 10⁸ ms^-1

Question 2

What is the fate of light when it strikes obliquely at a boundary separating 2 media?

2 points

Answer 2

It undergoes partial reflection and partial refraction
* A part of light goes back in the same medium obeying the laws of reflection
* remaining light enters the second medium in a straight line, but in a direction different from the initial

Question 3

Define refraction.

Answer 3

It is the change in direction of the path of light when it passes from one transparent medium to another transparent medium
it is a surface phenomenon.

Question 4

Why is the intensity/amplitude of refracted ray lesser than the incident ray?

Answer 4

Because part of the light gets reflected back into the same medium (obeying laws of reflection) while the rest passes through the boundary, into the new medium

Question 5

What causes change in direction of refracted ray?

Answer 5

Change in direction is caused due to change in the speed of light
slows down –> towards normal ; speeds up –> away from normal

Question 6

Does speed of light change when incident normally?

Answer 6

Yes speed changes but direction remains same

Question 7

State the Laws of Refraction

2 points

Answer 7

1. The incident ray, refracted ray, and normal at the point of incidence all lie on the same plane
2. The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant for the given pair of media

Question 8

What is refractive index?

2 definititons

Answer 8

• The refractive index of the second medium with respect to the first is defined as the ratio of the sine of the angle of incidence in the first medium to the sine of the angle of refraction in the second medium
• It is defined as the ratio of the speed of light in air to the speed of light in that medium

Question 9

1. Why does Refractive index have no unit?
2. why does frequency not change on refraction?

Answer 9

1. since its the ratio of 2 similar quantities.
2. because frequency depends on the source of light

Question 10

When light moves from rarer to denser medium what change takes place (WRT wavelength, velocity and frequency)

Answer 10

• Wavelength decreases since velocity decreases.
• Frequency remains the same.

Question 11

Refractive index of (i)glass (ii)water (iii)diamond

not sure we need this tbh

Answer 11

(i) 3/2 = 1.5
(ii) 4/3 = 1.33
(iii) 2.41

Question 12

Conditions for light ray to pass undeviated.

2 points

Answer 12

1. When angle of incidence at the boundary of the 2 mediums is 0˚
2. When the RI of medium 2 is equal to medium 1

Question 13

Relationship between wavelength of 2 mediums

Answer 13

Check TB pg-74 (cant write answer here)

Question 14

Factors affecting RI of a medium

3 points

Answer 14

• Nature of medium: Greater the speed of light in a medium, lesser the RI
• Temperature of medium: Greater the temperature of medium, lesser the RI of the medium
• Colour/wavelength of light: for a given medium V_r>V_v. therefore, RI_v>RI_r

Question 15

What is principle of reversibility of light?
Prove it using derivation

Answer 15

Principle of reversibility of light states that the path of a light ray is reversible
Derivation in pg-75

Question 16

what is lateral displacement of light?

Answer 16

when a light is passed through a glass block, the angle of incidence is equal to the angle of emergence due to which the emergent ray travels in the same direction as the incident ray but not in the same line. Hence it is laterally displaced.

Question 17

Why is incident and emergent ray parallel?

Answer 17

it’s because the glass slab’s opposite sides are parallel which makes the refracted angle at the first interface equal to the incident angle in the second interface. This causes the emergent ray to bend such that angle of incidence is equal to the angle of refraction. Therefore they’re parallel

Question 18

Factors affecting lateral displacement

Answer 18

1. Thickness of the medium: More the thickness of the medium, more the lateral displacement
2. Incident angle: Greater the angle of incidence, greater the lateral displacement.
3. Refractive index of medium: Greater the RI of the medium, more is the lateral displacement.

Question 19

What happens when you view an object from a thick mirror obliquely?

Answer 19

When an object is kept in front of a think mirror and viewed obliquely, a number of images are seen of which the second image is the brightest while others decrease in brightnness.