Chapter 31, Problem Q31.4DQ

Equation (31.14) was derived by using the relationship i = dq/dt between the current and the charge on the capacitor. In Fig. 31.9a the positive counterclockwise current increases the charge on the capacitor. When the charge on the left plate is positive but decreasing in time, is i = dq/dt still correct or should it be i = −dq/dt? Is i = dq/dt still correct when the right-hand plate has positive charge that is increasing or decreasing in magnitude? Explain.