Physics of the Ear (AQA A Level Physics)

Sketch an equal loudness curve on Figure 3 showing the normal response of a healthy ear.

Annotate the frequency axis with an appropriate scale.

Figure 3

Describe the procedure used to gather the data for an equal loudness curve.

Calculate the intensity of a sound that produces an intensity level of 30 dB.

A point source of sound has a power of 17 W.

Calculate, in dB, the intensity level at a distance of 12 m from the source.

The frequency of a sound is increased from 3.0 kHz to 8.0 kHz with no change in intensity.

One change in the sound perceived by a person with normal hearing is an increase in pitch.

Explain one other change to the sound perceived by the person as the frequency is increased from 3.0 kHz.

A sound wave produces a maximum increase in pressure on an ear of 2.5 × 10⁻³ N m⁻².

This causes a maximum increase in pressure in the fluid of the inner ear of 5.0 × 10⁻² N m⁻².

Explain how the ossicles contribute to this increase in pressure in the fluid of the inner ear.

The ear’s tympanic membrane can be assumed to be a circle of diameter 1.0 cm.

Calculate the area, in m², of the oval window.

A source of constant output power is used to generate a sound which is measured using a sound meter.

The dashed line in Figure 3 shows the intensity level curve over a range of frequencies with the meter set to the dB setting.

Figure 3

A student sketches a curve, over the same frequency range, which he thinks would be obtained when the meter is changed to the dBA setting. The curve drawn by the student is shown as the solid line in Figure 3.

Discuss whether the dBA curve drawn is correct.

Mesh barriers are set up to keep pedestrians at a safe distance from a noisy drill.

The maximum noise level which pedestrians should be subjected to is 110 dB.

The drill emits sound with a power of 7.8 W and acts as a point source.

The mesh barriers are set up a distance of 2.0 m from the drill.

Discuss whether this will keep pedestrians at a safe distance from the sound source.