Chapter 30, Problem 6P

Figure 30-37a shows a circuit consisting of an ideal battery with emf ℰ = 6.00 μV, a resistance R, and a small wire loop of area 5.0 cm². For the time interval t = 10 s to t = 20 s, an external magnetic field is set up throughout the loop. The field is uniform, its direction is into the page in Fig. 30-37a, and the field magnitude is given by B = at, where B is in teslas, a is a constant, and t is in seconds. Figure 30-37b gives the current i in the circuit before, during, and after the external field is set up. The vertical axis scale is set by i_s = 2.0 mA. Find the constant a in the equation for the field magnitude.

Figure 30-37 Problem 6.