A horseshoe magnet is placed on a top pan balance. A rigid copper wire is fixed between the poles of the magnet, as illustrated in Fig. 8.1. The wire is clamped at ends A and B. [Figure 8.1]

1. (a)(i)When a direct current is switched on in the wire, the reading on the balance is seen to decrease. State and explain the direction of: the force acting on the wire[3]
2. (a)(ii)the current in the wire.[2]
3. (b)A direct current of 4.6A in the wire causes the reading on the balance to change by 4.5 x 10⁻³ N. The direct current is now replaced by an alternating current of frequency 40 Hz and root-mean-square (r.m.s.) value 4.6 A. On the axes of Fig. 8.2, sketch a graph to show the change in balance reading over a time of 50 ms. [Figure 8.2][3]

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