chapter 14 - light

Question 1

1st law of reflection

Answer 1

incident ray, reflected ray and normal at the point of incidence lie on the same plane

Question 2

2nd law of reflection

Answer 2

angle of incidence is equal to the angle of reflection

Question 3

refraction

Answer 3

bending of light as it passes through from one optical medium to another

Question 4

1st law of refraction

Answer 4

incident ray, reflected ray and normal at the point of incidence lie on the same plane

Question 5

refractive index (of a medium)

Answer 5

ratio of the speed of light in a vacuum to the speed of light in that medium

Question 6

2nd law of refraction

Answer 6

for two given media, the ratio of the sine of angle of incidence to the ratio of the sine of angle of refraction is constant

Question 7

principle of reversibility of light

Answer 7

regardless of how many times a light ray has been reflected or refracted, it will follow the same path when its direction has been reversed

Question 8

total internal reflection

Answer 8

complete reflection of a light ray in an optically denser medium at the boundary with an optically less dense medium

Question 9

critical angle

Answer 9

the angle of incidence is an optically denser medium for which the angle of refraction is the less dense medium is exactly 90

Question 10

principal axis

Answer 10

the line which passes through the centre of the lens and is perpendicular to the plane of the lens

Question 11

optical centre C

Answer 11

the point on the principal axis that is the midpoint between the surfaces of the lens

Question 12

principal focal point F

Answer 12

the point on the principal axis where all the rays parallel to the principal axis meet after passing through the lens

Question 13

focal plane

Answer 13

the plane perpendicular to the principal axis on which all parallel rays meet after passing through the lens

Question 14

focal length L

Answer 14

the distance between the optical centre C and the principal focus point F

Question 15

real vs virtual image

Answer 15

real image can be formed on a screen placed at the image plane but a virtual image cannot be formed on a screen placed at its image plane

Question 16

extent of refraction of light from one medium to another

Answer 16

• from optically denser to optically less dense, bends towards normal (speed of light decreased)
• from optically denser to optically less dense, bends away from normal (speed of light in medium increased)

Question 17

when does total internal reflection occur

Answer 17

when light ray travels from an optically denser medium to an optically less dense medium, and when angle of incidence in optically is greater than critical angle.

Question 18

why does the light from the lamp emerge only from a circular area?

Answer 18

the light rays will get reflected back into the water when the angle of incidence is greater than the critical angle. as a result, light rays from the lampthat are able to reflected out of the water into the air ends up forming a cone with the base of the cone being the circular area on the water.

Question 19

why images produced by periscopes using mirrors are not as clear as images produced by periscopes using prisms

Answer 19

multiple images formed as there is a weak reflected ray and a
ray that is reflected off the reflecting surface and refracted out of the glass.

Question 20

using thicker lenses

Answer 20

image will be smaller and nearer to the lens. thicker lenses ahs a smaller focal length, hence light converges more adter passing through the lens.