(a)[2]
Ultrasound waves are unable to travel in a vacuum. Explain why.
(b)[2]
Describe in what way a longitudinal wave differs from a transverse wave.
(c(i))[3]
An ultrasound transmitter used in a medical scan emits an ultrasound wave with frequency 8.4 MHz. In soft human tissue, ultrasound moves at 1500 m s$^{-1}$. Calculate the wavelength of this ultrasound wave in soft human tissue.
(c(ii))[2]
The ultrasound wave moves from soft tissue into bone, where the ultrasound speed is higher than 1500 m s$^{-1}$. State what happens to the frequency and to the wavelength of the ultrasound wave when it enters the bone.