QUESTION
3. Consider the moving capacitor in problem 5.17 (Griffith's Introduction to Electrodynamics 4th edition):
Problem 5.17:
A large parallel-plate capacitor with uniform surface charge $\sigma$ on the upper plate and $-\sigma$ on the lower is moving with a constant speed $v$, as shown in Fig. 5.43.
FIGURE 5.43
Let h be the height of this capacitor.
a) What is the momentum that is stored (per unit area) between the plates?
b) Suppose that the upper plate of the capacitor moves slowly towards the lower plate of the capacitor at some speed u. What is the magnetic force on the upper plate of the capacitor that is due to this movement? Compare this force to the change in the momentum stored in the electromagnetic field.
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