O-LevelPhysicsLight5054/22 · Oct/Nov 2014 · Q1015 Marks

State the speed of light in air.

(a)State the speed of light in air.[1]
(b)Fig. 10.1 shows a ray of blue light passing from air into a glass block and refracting at the surface. [Figure 10.1 (not to scale)]
(b)(i)1.As the light enters the glass, state what happens to the speed of the light,[1]
(b)(i)2.the frequency of the light,[1]
(b)(i)3.the wavelength of the light.[1]
(b)(ii)On Fig. 10.1, mark and label the angle of incidence i and the angle of refraction r.[2]
(c)The refractive index of glass for blue light is 1.5.
(c)(i)A ray of blue light strikes the surface of a glass block at an angle of incidence of 89°. Calculate the angle of refraction of the light in the block.[3]
(c)(ii)Explain why the angle of refraction of blue light in glass is always less than 45°.[2]
(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°. [Figure 10.2]
(d)(i)Explain why the light continues in the same direction as it enters the glass block.[2]
(d)(ii)On Fig. 10.2, complete the path of the light until it leaves the glass.[2]

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 (Oct/Nov 2014). The mark or mark type is shown in brackets.

[1] 3.0 × 10⁸m/s
[1] decreases cao
[1] no change cao
[1] decreases cao
[1] i correctly marked (to normal)
[1] r correctly marked (to normal)
[1] sin i/ sin r = n or sin i/ sin r = 1.5
[1] sin 89/sin r = 1.5 or sin 89/1.5 or 0.67(0.666565)
[1] 42° or 41.8025°
[1] i equal to/close to 90° and r less than 45° (when sin i / sin r = 1.5)
[1] sin⁻¹(1/n)/sin⁻¹(1/1.5) (is approx 41.8°) OR r not be more than c
[1] (sin) i = 0 or ray enters directly/ along normal/perpendicular
[1] (sin) r = 0 or no refraction or wavefront/light hits surface all together all slows down together
[1] correct reflection at bottom surface (by eye)
[1] second correct reflection at top and no refraction at either point

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