Reflection, transmission and pulse-echo techniquesEdexcel International A Level Physics: Flashcards

What these 12 flashcards ask

What happens to a wave at an interface between two media?
What is a pulse-echo technique?
What is the pulse-echo equation for depth?
Why is t halved in d = vt / 2?
Why does ultrasound gel get used in scans?
Why are pulses used rather than a continuous wave?
How does wavelength limit the information from pulse-echo?
How can smaller detail be resolved?
How does pulse duration limit the information?
What time delay separates echoes from two surfaces a distance s apart?
Why is an echo weaker than the pulse emitted?
Name two uses of pulse-echo techniques.

Exam questions on Reflection, transmission and pulse-echo techniques

A hospital sonographer scans a patient using an ultrasound probe that emits very short pulses of ultrasound. A layer of gel is spread between the probe and the patient's skin. The same probe detects the pulses that are reflected back from inside the body.
Explain why the probe emits short pulses rather than a continuous beam of ultrasound.2 marks
A ship uses an echo sounder to measure the depth of the sea. It sends a short pulse of ultrasound downwards and detects the echo from the sea bed. The speed of ultrasound in seawater is 1.5 × 10³ m s⁻¹. A pulse sent by the ship returns from the sea bed 0.080 s after it was emitted.
Calculate the depth of the sea bed.2 marks
A medical ultrasound probe operates at a frequency of 2.5 MHz. The speed of ultrasound in soft tissue is 1540 m s⁻¹. A doctor wants to image a small structure in soft tissue that is 0.30 mm wide.
Calculate the wavelength of the ultrasound in the tissue.3 marks

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).