'A' Level Medical Option Questions - The Ear
(a) State what is meant by the threshold of hearing and state the frequency at which the reference threshold is quoted.
The threshold of hearing is the lowest intensity of sound that can be detected by the human ear. The reference intensity (1.0 × 10–12 W m–2) is taken at 1 kHz
(b) Sketch a curve on the axes below to show how the threshold of hearing varies with frequency across the full range audible to a normal human ear. Add a suitable frequency scale to the frequency axis.
Marks awarded for:
- basic shape
- range (20Hz – 20kHz approx)
- minimum between 1 kHz and 3 kHz
- scale, including units
(i) Calculate the intensity of a sound which is found to have an intensity level of 60 Db above the threshold of hearing. The intensity of the threshold of hearing is 1.0 × 10–12Wm–2.
I2 = 106 I1
= 106 × 1.0 × 10–12
= 1.0 × 10–6 W m–2
(ii) The smallest increase in sound intensity which the human ear can detect is about 12%. Express this change in decibels.
number of dB = 10 log10 (I2/I1)
= 10 log10 (112/110)
= 0.5 dB
(Total 11 marks)