A laser produces a beam of red light. (a) The red light from the laser has a frequency of 4.3 × 10¹⁴Hz.

1. (a)(i)State the speed of light in air. ...............................................................................................................................................[1][1]
2. (a)(ii)Calculate the wavelength of this red light in air. wavelength = ..............................................................[2][2]
3. (b)Red light from the laser strikes one side of a glass prism at an angle of incidence i. The light refracts towards the normal as it enters the prism. Fig. 10.1 shows the prism, the light and a screen. [Figure 10.1]
4. (b)(i)State what happens to the speed of light as it enters the glass. ...............................................................................................................................................[1][1]
5. (b)(ii)The refractive index of the glass is 1.5. The angle of refraction in the glass, where the light enters the prism, is 30°. Calculate the angle of incidence i. i= ....................................................................[2][2]
6. (b)(iii)The light then passes back into the air and strikes the front of the white screen, as shown in Fig. 10.1. Calculate θ, the angle between the ray in air and the side of the prism. θ= ....................................................................[1][1]
7. (c)The laser in (b) is replaced with a filament lamp and a slit, as shown in Fig. 10.2. [Figure 10.2] A ray of white light now strikes the prism.
8. (c)(i)On Fig. 10.2, draw what happens to the light as it passes through the prism and strikes the screen. [2][2]
9. (c)(ii)Describe what is seen on the screen. ............................................................................................................................................... ...............................................................................................................................................[2][2]
10. (c)(iii)In addition to visible light, the filament lamp also emits some infra-red radiation. This infra-red radiation is able to pass through glass.
11. (c)(iii)1.On the screen in Fig. 10.2, mark an X to indicate a place where infra-red radiation strikes the screen. [1][1]
12. (c)(iii)2.Infra-red radiation is often detected by using a sensitive thermometer with a bulb that has been painted black. Explain why the blackened bulb makes the thermometer a good detector of infra- red radiation. ...............................................................................................................................................[1][1]
13. (d)Explain the role played by infra-red radiation in intruder alarms. ............................................................................................................................................... ...............................................................................................................................................[2][2]

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