Accelerating charges

QUESTION:

Which one of the following will NOT generate electromagnetic waves or pulses?
(a) direct current
(b) accelerating electron
(c) proton in simple harmonic motion
(d) alternating current
(e) charged particles travelling in a circular path in a mass spectrometer.

Answer

Lets look at each answer in turn.
(a) a direct current will generate a magnetic field but since the charge carriers are not accelerating there will be no electromagnetic waves or pulses
(b) an accelerating electron is obviously accelerating and accelerating charges will generate electromagnetic waves
(c) a proton performing s.h.m is accelerating and so will generate electromagnetic waves and pulses
(d) in alternating current the charge carriers continually change direction and so will be accelerating. This means that they will generate electromagnetic waves and pulses
(e) charged particle performing circular motion are in a constant state of acceleration and so will generate electromagnetic waves

Therefore (a) is the right answer.