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'A' Level Medical Option Questions - The Ear

Q7. A ship sounds its foghorn. A person on a cliff hears the sound which has an intensity of 0.13 mW m–2. The sound suffered attenuation in travelling between the ship and the person.

(a)

(i) Define intensity.

Intensity is the power per unit cross-sectional area (in path of wave)

(ii) State what is meant by attenuation and what causes it.

Attenuation is the reduction in intensity/energy/power of the wave as it travels through a medium. This is due to absorption/scattering/diffraction.

(3 marks)

(b) Calculate the intensity level of the sound heard by the person described above.

threshold of hearing I0 = 1.0 × 10–12 W m–2

I0 = 1.0 × 10–12 W m–2

intensity level = 10 log10(I/Io)

= 10 x log10 (0.13 x 10-3/(1.0 x 10-12))

= 10 x log10 (1.3 x 108)

intensity level = 81 dB

(2 marks)

(Total 5 marks)