14.2-Reflection of Light, Paper 2 (Section B)

Question 1

State the speed of light in air

Answer 1

3.0 x 10^8 m/s

Question 2

Fig 10.1 shows a ray of blue light passing from air into glass block and refracting at the surface. (14.2) pg 1 (theory B)

i) As the light enters the glass, state what happens to:
1. the speed of light,
2. the frequency,
3. the wavelength of the light
ii) On fig 10.1 mark and label the angle of incidence, i and the angle of refraction, r

Answer 2

i)
1.decreases cao
2.no change cao
3.decreases cao
ii)
1. i correctly marked (to normal)
2. r correctly marked (to normal)

Question 3

(c) The refractive index of glass for blue light is 1.5
i) A ray of blue light strikes the surface of a glass block at an angle of incidence oof 89 degree
- Calculate the angle of refraction of light in the block
ii) Explain why the angle of refraction of blue light in glass is always less than 45 degree

Answer 3

(c) sin i/sin r, r=n 
     sin i/ sin r =1.5
     sin 89/ sin r=1.5 
     sin 89/1.5 or 0.67
     42 degree 
ii)i equal to/close to 90 degree and r less than 45 degree
   sin i/ sin 45 = 1.5

Question 4

(d) Blue light, travelling in air strikes the side of a different glass block and continues in the same direction as it enters the glass block. fig 10.2 shows the ray of light and the shape of the glass block. The critical angle for this glass is 42 degree
(14. 2) pg 2 (theory B)
i) Explain why the light continues in the same direction as it enters the glass block
ii) On fig 10.2 complete the path of the light until it leaves the glass

Answer 4

i)light enters at the normal, 90 degree

Question 5

Fig 9.1 shows a man in a room looking into a mirror, as view from above. (14.2) pg 3 (theory B)
a) The man can see an image of part of the wall AB in the mirror
Point C is the point on the wall closest to A that the man can see by reflection in the mirror.
This point is not marked on fig 9.1
i) On fog 9.1 find the point C and draw a ray of light from C which enables the man to see the image of C
ii) On the ray that you have drawn on fig 9.1 label the angle of incidence, i and the angle of reflection, r
iii) One characteristics of the image formed by the mirror id that it is virtual
1. Explain what is meant by a virtual image
2. State one other characteristic of an image formed by a plane mirror

Answer 5

(a)
i)ray from right-hand corner of mirror to eye/ any incident and corresponding reflected ray correct by eye
ii)normal drawn at any inetrsection of incident and reflected ray/ both r and i labelled correctly with normal
iii)
1.cannot be formed on a screen or nothing at the image (position)/rays do not come (all the way) from image or rays only appear to come from image
2.(same direction) behind the mirror or same size or uptight or laterally inverted

Question 6

(b) Light travels along the optical fibres by the total internal reflection
i) State 2 differences between total internal reflection and reflection in a mirror
ii) The critical angle for the light travelling form the material of the fibre to air is 44 degree
-calculate the refractive index of the material in the fibre
iii) Light enters the optical fibre from air with an angle of incidence of 50 degree
-calculate the angle of refraction
iv) Optical fibres are used in telecommunications to send large amounts of data
Pulses of light travel at almost the same speed along a fibre as electrical pulses travel along metal wire
State 2 advatages of using optical fibres rather than wires for transmitting data

Answer 6

(b)
i)-reflection in mirror occurs at any angle angle
or total internal reflection (TIR) only occur for i >critical angle
or there is no critical angle for the mirror B1
-TIR occurs from dense to less dense medium
or in the dense (r) medium
or from glass to air or inside/does not escape glass
or from slow to fast
or mirror reflection from air to glass B1
-(mirror) reflection is not total,e.g not all reflected
or better quality of image
or multiple images from a mirror