Light

Question 1

Law of Reflection of Light

Answer 1

1. The angle on incidence is equal to the angle of reflection.
2. The incident ray, reflected ray and normal all lie on the same plane.

Question 2

5 characteristics of image formed due to reflection in a plane mirror

Answer 2

1. It is a virtual image.
2. Image distance is the same as object distance.
3. it is of the same size as the object.
4. It is laterally inverted.
5. It is upright.

Question 3

Real image

Answer 3

It can be captured on a screen and is formed by the intersection of light rays from the object at the screen.

Question 4

Virtual image

Answer 4

It cannot be captured on a screen and is formed by intersection of light rays that appear to come from the image.

Question 5

Refraction of light

Answer 5

The bending of light as it passes from one optical medium to another due to the change in the speed of light.

Question 6

Refractive index, n

Answer 6

speed of light in vacuum/speed of light in medium

Question 7

Refractive index (given that one medium is air)

Answer 7

sin i/sin r
angle i is the angle measured in the air.

Question 8

Critical angle

Answer 8

The angle of incidence in an optically denser medium for which the angle of refraction in the optically less dense medium is 90°.

Question 9

Law of Refraction of Light

Answer 9

1. The incident ray, refracted ray and the normal at the point of incidence all lie in the same plane.
2. For two given mediums, the ratio of sine of the angle of incidence to the sine of the angle of refraction is a constant.

Question 10

Total internal reflection

Answer 10

The complete reflection of a light ray inside an optically denser medium at its boundary with an optically less dense medium.

Question 11

Conditions for Total Internal Reflection

Answer 11

1. Light ray should be inside the optically denser medium, heading towards the boundary with an optically less dense medium.
2. Angle of incidence, i, in the optically denser medium should be greater than the critical angle of that medium.

Question 12

Application of Total Internal Reflection

Answer 12

Optical fibres in telecommunication industries

Question 13

Advantage of optical fibres

Answer 13

1. They can carry much more information than copper wires.
2. They experience less signal loss.
3. They are also lighter than copper wires.
4. They are becoming cheaper to manufacture than copper wires.

Question 14

Focal length

Answer 14

Distance between the optical centre and the principal focus of the lens.

Question 15

Behaviour of light rays

Answer 15

1. Virtual/real
2. magnified/diminished/same size
3. upright/inverted
4. same/opposite side of the lens as the object

Question 16

Thin Lens Equation (for converging lens)

Answer 16

1/f = 1/u + 1/v

Question 17

Linear magnification

Answer 17

Ratio of the height of the image to the height of the object.