32. Electromagnetic Waves

Show that displacement current, ε₀ (dΦE/dt), has the SI units of amperes.

If a galaxy is traveling away from us at 2.2% of the speed of light, roughly how far away is it?

Suppose a 25-kW radio station emits EM waves uniformly in all directions. How much energy per second crosses a 1.0-m² area 1.0 km from the transmitting antenna?

When estimating the distance to lightning, you can time how long after the light flash is seen until the thunder is heard. Sound travels 343 m/s, so a good estimate is to allow 3.0 seconds per kilometer. There is actually a small mistake with this method because the time for the light to travel is not accounted for. How big is this mistake (%) for a lightning flash 2.0 km away?

The average intensity of a particular TV station’s signal is 1.0 x 10^-13 W/m² when it arrives at a 33-cm-diameter satellite TV antenna. (a) Calculate the total energy received by the antenna during 3.0 hours of viewing this station’s programs. (b) Estimate the amplitudes of the E and B fields of the EM wave.

The nearest neighboring star to the Sun is about 4 light-years away. If a planet happened to be orbiting this star at an orbital radius equal to that of the Earth–Sun distance, what minimum diameter would an Earth-based telescope’s aperture have to be in order to obtain an image that resolved this star–planet system? Assume the light emitted by the star and planet has a wavelength of 550 nm.