32. Electromagnetic Waves

How practical is solar power for various devices? Assume that on a sunny day, sunlight has an intensity of 1000 W/m² at the surface of Earth and that a solar-cell panel can convert 20% of that sunlight into electric power. Calculate the area A of solar panel needed to power (a) a calculator that consumes 50 mW (b) a hair dryer that consumes 1875 W.

How practical is solar power for various devices? Assume that on a sunny day, sunlight has an intensity of 1000 W/m² at the surface of Earth and that a solar-cell panel can convert 20% of that sunlight into electric power. Calculate the area A of solar panel needed to power (c) a car that would require 120 hp. (d) In each case, would the area A be small enough to be mounted on the device itself, or in the case of (b) on the roof of a house?

We saw earlier (Chapter 19) that the rate energy reaches the Earth from the Sun (the “solar constant”) is about 1.3 x 10³ W/m². What is (a) the apparent brightness b of the Sun, and (b) the intrinsic luminosity L of the Sun?

Suppose a 25-kW radio station emits EM waves uniformly in all directions. What is the rms voltage induced in a 1.0-m-long vertical car antenna (c) 1.0 km away, (d) 50 km away?

At one instant, the electric and magnetic fields at one point of an electromagnetic wave are $E=(200\hat{i}+300\hat{j}-50\hat{k})\text{ V/m}$ and $B=B_0(7.3\hat{i}-7.3\hat{j}+a\hat{k}\mu T$. What is the Poynting vector at this time and position?