Some waves are electromagnetic.

Which of these physical quantities is identical for all electromagnetic waves propagating through a vacuum?

• A: Photon energy
• B: Wave speed
• C: Oscillation frequency
• D: Spatial wavelength

Match each type of electromagnetic wave with its correct application.

• Wave types: Microwaves, X-rays, Gamma rays
• Applications: Mobile phone communications, internal bone imaging, high-dose cancer radiotherapy

Electromagnetic waves are transverse waves. Describe how the oscillations of a transverse wave relate to the direction in which the wave travels.

Sound waves and light waves behave differently when transitioning between media.

Infrasound waves are acoustic waves with frequencies below the lower limit of human hearing. Which of these could be the frequency of an infrasound wave?

• A: 14 Hz
• B: 140 Hz
• C: 1400 Hz
• D: $14000Hz$

A laser rangefinder calculates the distance, $d$, to a target wall using the time, $t$, between emitting a light pulse and detecting its reflection:

where $c$ is the speed of light. Explain why the factor of $\frac{1}{2}$ is used in this equation.

The speed of light in glass is slower than the speed of light in air. Explain how this decrease in speed affects the wavelength of the laser light when it passes from air into glass, assuming its frequency does not change.