(a(i))[2]
State what is meant by ultrasound and give a value for the lowest possible frequency of ultrasound waves.
(a(ii))[2]
State which of these waves are electromagnetic, and longitudinal.
(b)[3]
The ultrasound wave moves through the flesh to point X and then across the thickness of the bone to point Y. At Y, part of the ultrasound is reflected and travels back to X. The total time for ultrasound to travel in the bone from X to Y and back to X is $9.0 \times 10^{-6}\,\text{s}$. The speed of ultrasound in bone is $4100\,\text{m s}^{-1}$. Calculate the thickness $t$ of the bone.