For the configuration in Ex. 10.1, consider a rectangular box of length l, width w, and height h, situated a distance d above the yz plane (Fig. 10.2).
(a) Find the energy in the box at time t1 = d/c, and at t2 = (d + h)/c.
(b) Find the Poynting vector, and determine the energy per unit time flowing into the box during the interval t1 < t < t2.
(c) Integrate the result in (b) from t1 to t2, and confirm that the increase in energy (part (a)) equals the net influx.
In this problem, we have energy in the box at time , the Poynting vector and integrate the result.