So this person makes a coil of wire, which she connects to a power supply and switches on to make an electromagnet. She places two iron bars inside the coil, end to end. She holds the ends of the iron bars. With the switch closed, she finds that its difficult to pull the two bars apart.So first off, how come they were attracted to each other? And if she were to switch off the current and try to pull the bars apart, what would happen, or what would be noticed? Finally, if this experiment was repeated with brass bars instead of iron ones, what differences would their be? I honestly just don‘t understand! Thanks so much for you‘re help! :)
The electromagnetic field created by the coil and electricity, let electrons flow in the two bars (end to end) for micro time until the bars charge is in equilibrium with the magnetic field (part of bars electrons move in one direction and its number is related to the e.m. field power) and these bars become as capacitor (charge holder under this field) and the two bars are attracted because of the charge under the field [ +++ ++ + - -- ---] ( electron flow direction is - ). + and – attract each other. Turn off the current the iron still in charge slightly and you feel the two bars turned into two magnetic pieces. In the case of copper, the electron return rapidly to their places after the e.m. field was removed. And no charge difference in the two bars and no attraction will happen.
The phenomenon is called induced magnetism it is similar to induced charge in electrostatics but not identical. Every bar of magnetic material has many tiny magnetic domains all pointing in random directions. When a field is applied to the bars then some of these domains start to line up causing the bars to become magnets. What happens when the current is turned off depends on the particular iron. In Soft iron the domains relax and become random again. In hard iron the domains tend to stay where they have been placed so they remain magnetic. Other materials that are not of a magnetic type cannot have magnetism induced in them.,
