Answer:
the correct answer is: The magnitude of the current varies with time.
Explanation:
The movement of a filament by a current is due to the electric force when electrons accumulate on one side attract positively charged nuclei.
In this case the voters in a period of time are on one side, let's call it forward and in another period of time it accumulates on the other side, let's call it back, this explains the very small movement of the filament, therefore we have a current that varies over time.
The other two options are not correct because turning off the current the filament goes to the central position and does not go back, the other explanation the current goes in one direction or another, the voters are always on the same side therefore the filament only goes in a sense.
Consequently the correct answer is: The magnitude of the current varies with time.
