The right answer is
all of the above
good luck
Answer:
when the direction of the Current changes.
Explanation:
Electromagnet refers to an iron ore wrapped around with a coil of wire, in presence of electric current. As it acts like a magnet, when current is passed through it.
The north & south poles of magnetic fields produced by such magnet, change with direction of current passed through it.
I'm not accurately sure if you're asking for why the bulb of a thermometer is in a cylindrical shape. So let me continue. The shape of the which is thin and cylindrical in the shape is the increase of the effect of mercury in the tube to rise and fall depending on the contact temperature.
