15-Electromagnetic Spectrum, Paper 2 (Section B)

Question 1

A laser produces a beam of red light.
(a) The red light from the laser has a frequency of 4.3 x 10 ^14 Hz
i) State the speed of light in air
ii) Calculate the wavelength of this red light in air
(b) Red light from the laser strikes 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 (15) Pg 1 (theory B)
i) State what happens to the speed of lights as it enters the glass
ii) The refractive index of the glass is 1.5. The angle of refraction in the glass, where the light enters the prism, 30 degree.
Calculate the angle of incidence i
iii) The light then passes back into the air and strikes the front of the white screen, as shown in fig 10.1 (15) Pg 2 (theory B)
Calculate the angle between the ray in air and the side of the prism.
(c) The laser in (b) is replaced with a filament lamp as a slit, as shown in fig 10.2 (15) Pg 2 (theory B)
A ray of what light now strikes the prism
i) On fig 10.2 draw what happens to the light as it passes through the prism and strikes this screen
ii) Describe what is seen on the screen
iii) In addition to visible light, the filament lamp also emits some infra-rede radiation. This infra-red radiation is able to pass through glass.
1. On the screen in gig 10.2 mark an X to indicate a place where infra-red radiation strikes the scree
2. Infra-red radiation is often detected by using a sensitive thermometer a good detector of infra-red radiation
(d) Explain the role played by infra-red radiation in intruder alarms