O-LevelPhysicsLight5054/21 · May/June 2015 · Q55 Marks
Fig. 5.1 shows a ray of light entering and passing along an optical fibre. [Figure 5.1]
- (a)Calculate the refractive index of the glass in the optical fibre.[2]
- (b)Explain why the ray of light is totally internally reflected at A.[2]
- (c)Both optical fibre and copper wire are used to transmit data. Optical fibre is cheaper and can carry more data per second than copper wire. State one other advantage of using optical fibre rather than copper wire to transmit data.[1]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme (May/June 2015). The mark or mark type is shown in brackets.
- [1] sin i/sin r or sin 50/sin 30
- [1] 1.5(321)
- [1] moving from more dense to less dense medium or moving to lower refractive index (air)
- [1] angle of incidence is greater than critical angle
- [1] less heat loss/more efficient or less chance of hacking / more secure / less interference or less reduction in signal/less need for boosting/larger distances possible/thinner or less bulky
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