The laser’s red light has a frequency of $4.3 \times 10^{14}\,\text{Hz}$. State the speed of light in air.
Calculate the wavelength in air of this red light.
State what happens to the speed of light as it enters the glass.
The refractive index of the glass is $1.5$. The angle of refraction in the glass, at the point where the light enters the prism, is $30^{\circ}$. Calculate the angle of incidence $i$.
The light then passes back into the air and strikes the front of the white screen, as shown in Fig. 10.1. Calculate $\theta$, the angle between the ray in air and the side of the prism.
On Fig. 10.2, draw the path of the light as it travels through the prism and onto the screen.
Describe what appears on the screen.
On the screen in Fig. 10.2, mark an X to show where infra-red radiation strikes the screen.
Explain why the blackened bulb makes the thermometer a good detector of infra-red radiation.
Explain the role played by infra-red radiation in intruder alarms.