What produces an electromagnetic wave?
a) an oscillating or accelerating electric charge
b) an electric charge moving at constant velocity
c) a static electric charge
d) a magnetic monopole moving at constant velocity

A

Explanation:

Let's rule out some of the options. C makes no sense because static charges will create electric fields only, so the charge has to move. D makes no sense because monopoles do not exist. We can rule out B because when a charge is moving at a constant velocity. You can use Maxwell's equations and general relativity to figure out that at a constant velocity, you can't produce an electromagnetic wave because there is no magnetic field. Therefore the answer is A. When you have an oscillating or accelerating electric charge, you will produce an EM wave.

when a device is used in a circuit in which the voltage is 81 v, the current flowing through the device is 3 a. what is the resistance of the device?

a. 27 ω

b. 40.5 a

c. 243 ω

d. 243 a

the correct answer is a. 27