The Physics of Waves: Light Waves, Sound Waves and Ultrasound

“Ground state” is the state of lowest energy; hence, it can only move to a higher energy state. In this case it is said to be excited.

The change in frequency when the source of the (say) sound is in motion relative to the observer is called the Doppler effect. (The red shift in astronomy is due to the Doppler effect.)

Choice C is in reverse order; in choice A, UVC has higher frequency than UVA; it is possible for an X-ray frequency (e.g. from a hospital linear accelerator) to be higher than a particular gamma ray (e.g. from radioactive technetium).

Microwaves are low-frequency EM radiation, while UV radiation is relatively high. The frequencies of visible light are between the two.

Which combination of frequency and wavelength will give the speed 2 × 10⁸ m/s? v = fλ = 5 × 10¹⁴ Hz × 4 × 10−⁷ m = 20 × 10^14–7 = 20 × 10⁷ = 2 × 10⁸

Frequency and wavelength are related, as are amplitude and intensity.

1 B = 10 dB. Each time sound intensity increases by a factor of 10, sound level increases by 1 B. Thus if a sound is 2 B (20 dB) louder, it is 10 × 10 = 100 times louder.

Ultrasound, and audible sound, is a longitudinal wave. It is neither ionising nor electromagnetic.

UV radiation is absorbed by the eye lens, and the energy of the absorbed photons can break the bonds between atoms.

An alternating current (one whose direction reverses direction frequently in a second) will produce a changing (oscillating) magnetic field, whereas a steady current will produce a steady magnetic field.