can an inductor be used to filter out variation in current?

Answer 1

You bet, that is one of its major uses. Think about it this way. the voltage across an inductor is given by

v = L * di/dt

If the current has a positive di/dt, the voltage across the inductor is positive. This means that the inductor will reduce the voltage at its output (the inductor voltage will subtract from the voltage at is input). If the current has a positive di/dt, the voltage across the inductor is negative. This means the inductor will increase the voltage at is output (the inductor voltage will add to the voltage at is input).

Answer 2

if by "variation in current" you mean taking powerline ripple out of a DC power supply, that is correct. However if you have a load that sometimes draws less current, and sometimes more, as an audio power amplifier, the inductor would have to be of humongous size to compsate over a period of even one second. In this case a ballast tube (light bulb) would provide a more consistant current load to the supply.