Chapter 14 Light

Question 1

What are the six characteristics of a plane mirror?

Answer 1

• Image is virtual.
• Image is upright.
• Image is same size as object.
• Image is laterally inverted.
• Image will be same distance from the mirror as the object is from the mirror.

Question 2

why do light rays refract?

Answer 2

Light rays bend due to the difference in speed of light in different optical
mediums.

Question 3

what happens when light travels from a less dense to denser medium?

Answer 3

the refracted ray will bend towards the normal

Question 4

what happens when light travels from a denser to a less dense medium?

Answer 4

the refracted ray will bend away from the normal

Question 5

can the refractive index be less than 1?

Answer 5

nuh uh

Question 6

what are the two formulas for refractive index?

Answer 6

n=sini/sinr and n = speed of light in vacuum* (c) / speed of light in medium (v)

*speed of light in vacuum is 3 x 108 ms-1

Question 7

what is the first law of refraction?

Answer 7

it states that the incident ray, refracted ray and the normal at the point of incidence all lie in the same plane

Question 8

what is the second law of refraction?

Answer 8

it states that for two given media, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant, that is sini/sinr = constant

Question 9

what is the principle of reversibility?

Answer 9

it states that light will follow the same path even if its direction of travel is reversed.

Question 10

when do we use sinr/sini?

Answer 10

if the light ray is travelling from a denser to less dense medium (principle of reversibility)

Question 11

when does toa, internal reflection occur?

Answer 11

when the angle of incidence exceeds the critical angle, causing the light ray to not leave the optically denser medium and instesd, reflect internally.

Question 12

what is the critical angle?

Answer 12

the angle of incidence in the optically denser medium for which angle of refraction in the opticslly less dense medium is exactly 90 degrees

Question 13

formula for critical angke:

Answer 13

sinc = 1/n

Question 14

what are thetwo conditions for total internal reflection

Answer 14

1) Light ray must be travelling from optically denser medium to an optically less dense medium (so that it bends away from the normal until it hits 90°)
2) angle of incidence must be greater than the critical angle

Question 15

what are optical fibres?

Answer 15

they are made from glass or plastic, and can carry information in the form of coded light pulses .

Question 16

how do optical fibres work?

Answer 16

The light ray entering the pipe does not exit but is constantly undergoing total internal reflection until it reaches the other end of the fibre.

Question 17

what isthe principal axis ?

Answer 17

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

Question 18

what is the optical centre C?

Answer 18

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

Question 19

what is the principal focal point f

Answer 19

Point on the principal axis to which an incident beam parallel to the principal axis converges to.

Question 20

what is the focal length f

Answer 20

Distance between its optical centre and principal focus F