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

The impedance difference between the air and skin is large, so most of the ultrasound would reflect from the skin, rather than enter the body. Using gel avoids the ultrasound passing through air.

The ability to vaporise tissue means a laser can “cut” through tissue at the point of vaporisation.

Rearrange the wave equation for wavelength: v = fλ so λ = v/f. Then substitute: λ = 330 m/s ÷ 1000 Hz = 0.33 m = 33 cm.

A Doppler “stethoscope” produces ultrasound and detects the reflected ultrasound from moving red blood cells (or the moving heart wall). The motion of the object reflecting the ultrasound causes the reflected ultrasound to be shifted in frequency. Its depth of penetration in human tissue decreases as its frequency increases.

While UVC has higher energy than UVB and therefore is potentially more damaging, however, UVC does not reach the ground as it does not penetrate the Earth’s atmosphere.

Sound waves require a medium. Longitudinal waves oscillate parallel to their direction of propagation. Electric and magnetic fields are not involved. Choice C is correct but not specific enough.

Beat frequency is the difference between the two frequencies. 5 000 000–5 002 500 = 2500 Hz. The frequency of the beats is within the audible range so we can hear them.

Energy and amplitude are directly related.

A convex or converging lens is “fat” in the middle.

Frequency and period are inversely related, so as frequency decreases the period of the wave will increase.