Ultrasound scans are used to obtain images of internal organs. Before the scan is carried out, a layer of gel is applied to the patient's skin.
Which statement best explains why the scan fails to produce a useful image if the gel is not used?
Air trapped between the transducer and the skin reflects almost all the ultrasound waves.
Air absorbs the ultrasound waves and converts them into heat before they reach the organs.
The gel is needed to lubricate the skin so that the transducer can vibrate at a higher frequency.
Without the gel, the ultrasound waves speed up too much in the skin and cannot be detected.
11 exam-style questions on OCR GCSE Physics Wave interactions. Each one has a worked solution and a mark scheme showing where the marks go.