A loudspeaker is made from a coil of wire fixed to a cardboard tube. The tube is attached to a cardboard cone. Fig. 8.1 shows part of the arrangement of the loudspeaker. [Figure 8.1] When there is a current in the coil, the coil experiences a force.

1. (a)State what else is needed in a loudspeaker to make a current-carrying wire experience a force.[1]
2. (b)(i)A student connects the coil to the output of an alternating current (a.c.) generator. Fig. 8.2 shows how the electromotive force (e.m.f.) produced by the generator varies with time. [Figure 8.2] The coil, tube and cone vibrate backwards and forwards. Explain why the e.m.f. shown in Fig. 8.2 makes the coil vibrate.[2]
3. (b)(ii)The vibrating cone produces sound in the surrounding air. Explain, in terms of molecules, how the cone produces a sound wave that travels through the air.[3]
4. (b)(iii)Sound is a longitudinal wave. Describe the difference between a longitudinal wave and a transverse wave.[2]
5. (b)(iv)Using Fig. 8.2, determine the number of times that the cone reverses its direction of motion in 1.0s.[2]
6. (b)(v)The speed of sound in air is 340m/s. Calculate the wavelength of the sound. wavelength =[2]
7. (c)(i)The student adjusts the generator so that the maximum voltage of the output is now 3.0V. Everything else stays the same as the output shown on the graph in Fig. 8.2. Explain any effect on the loudness of the sound.[2]
8. (c)(ii)Explain any effect on the pitch of the sound.[1]

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