'A' Level Medical Option Questions - The Ear
Q9. A patient has a hearing test to obtain an equal loudness curve at a level above the threshold of hearing. The curve obtained is shown below.
(i) Describe how such a curve is obtained.
The patient must listen to a sound at a frequency of1 kHz and an intensity level of 10 dB. That is the 'loudness' that is to be used as the reference level for the test. The patinet must the listen to a sound at a different frequency and the lintensity level must be adjusted until the patient says the loudness is the same as the reference one. This is then repeated for several frequencies between 20 Hz and 20 kHz to obtain the curve.
(ii) On the graph draw an equal loudness curve which passes through 100 dB at a frequency of 1 kHz.
An equal loudness curve to show:
a line that i salmost flat at 100 dB
with dip at 3 kHz
(i) Define the threshold of hearing, I0
The minimum intensity of sound that can be heard by normal human earat a frequency of 1 kHz
(ii) A drill is heard by a passer-by. The intensity of the sound reaching the passer-by is 1.3 × 10–3 W m–2. Calculate the intensity level of the sound heard.
I0 = 1.0 × 10–12 W m–2
intensity level = 10 log10(I/Io)
= 10 x log10 ((1.3 x 10-3)/(1.0 x 10-12))
= 10 x log10 (1.3 x 109)
intensity level = 91 dB
(Total 9 marks)