Acoustic Phenomena: Loudness, Pitch and the Doppler Shift in Blood

In the paper

Unit 3 carries 8 of the 50 physics marks; with six chapters sharing them, this one averages a little over one (MEC publishes weights by unit, not by chapter). For a medical entrance it is the chapter with the most obvious clinical hook: the cardiologist who reports a jet of 4 m s⁻¹ across a mitral valve has read it off a Doppler frequency shift, and an obstetric ultrasound scan is the inverse-square law and the reflection of sound put to work.

The MEC scope lines are: Pressure amplitude; intensity, loudness, quality and pitch; Doppler effect: concept, calculations and applications. The two headings below are those points, in MEC's order.

Three ways it is asked: recall (the reference intensity of the decibel scale, which characteristic goes with waveform, the audible range); understanding (why a loudness doubling is not an intensity doubling, why a source moving at u and an observer moving at u do not give the same shift, why an echo needs 17 m); application (a decibel change from an intensity ratio, an apparent frequency from a moving whistle, a blood velocity from an ultrasound shift, a distance from an echo's delay).