Question

18. A loudspeaker is constructed from a circular, concentric permanent magnet that produces a radial magnetic field of flux density B-0.8T, as shown in the front view in Figure 8A. In the circular gap between the poles, a circular coil of radius 16 mm is placed, and attached to a moveable cone which produces the sound at the front of the speaker (see Figure 8B, sectional view). The coil consists of 30 turns of copper wire (only 8 shown in Figure 8B for clarity), whose radius is 0.1 mm and conductivity is 6 x 10⁷ S/m 

 (a) What is the total resistance of the copper wire coil? 

(b) If the coil carries a current of 4 A in a clockwise direction with respect to the view in Figure 8A, what is the magnitude and direction of the force exerted on it? State the direction with respect to Figure 8A- e.g. upwards, to the left, into page, out of page, etc 

(c) If the same coil is taken out from the loudspeaker and placed in a different magnetic field so that it is oriented perpendicular to it, and that magnetic field is uniform with a strength B that increases linearly from OT at time t = 0 sec to 6 T at time t = 0.5 sec, what is the induced voltage in the coil during that half-second period?

Answer 1