Waves at interfaces and pulse-echoEdexcel A-Level Physics: Mind map

Exam questions on Waves at interfaces and pulse-echo

1. A sonographer is carrying out an ultrasound scan of a patient. She applies a layer of gel to the skin before pressing the transducer against it. The transducer emits ultrasound of frequency 3.5 MHz, which travels through soft tissue at 1540 m s⁻¹.
   Calculate the wavelength of the ultrasound in soft tissue.2 marks
2. In a pulse-echo scan, a transducer sends a short pulse of ultrasound into soft tissue, where the speed of ultrasound is 1540 m s⁻¹. An echo from the boundary of an organ is detected 78 μs after the pulse was transmitted.
   The transducer sends pulses at regular intervals. Explain why the interval between pulses must be longer than the time for the echo from the deepest boundary to return.2 marks
3. A pulse-echo system uses ultrasound of frequency 5.0 MHz. Each pulse lasts 0.40 μs. The speed of ultrasound in the tissue being scanned is 1540 m s⁻¹.
   Calculate the wavelength of the ultrasound and the length of one pulse in the tissue.3 marks