Question

A dish antenna with a diameter of 15.0 m receives a beam of radio radiation at normal incidence.

The radio signal is a continuous wave with an electric field given by:

E = 0.75 sin[(0.838/m)x − (2.51 × 108 /s)t] N/C.

Here, x is in meters and t is in seconds. Assume that all the radiation that falls on the dish is absorbed.

(a) Calculate the speed of the radiation. Don’t assume it must be equal to c: use the equation above to calculate this speed.

(b) Calculate the amplitude of the magnetic field of this wave.

(c) Calculate the Poynting flux of the radiation.

(d) Suppose the beam that is entering this dish has the same diameter as the dish. Suppose a pulse of radiation that lasts for 10.0 ns travels along the beam and into the dish. This pulse has an energy density of 1.0 × 10−9 J/m 3 . How many Joules from the pulse does the dish absorb?

Answer 1