How is induced current produced

Since electrons were moving and spinning within atoms, ferromagnetism could now be explained by the motion of charges within different materials. If all of the electrons in an object line up with their spins in the same direction, the spins will add and create an observable field. That last sentence is slightly unrealistic. Solids contain incredably large numbers of electrons, and they will never all completely line up.

Instead, a solid generally consists of magneticdomains. In a domain, the majority of electrons which can unpaired valance electrons will have spins aligned. Adjacent domains will generally not be oriented in identical directions. In magnetized materials, some domains will cancel, but the average domain orientation will be in one direction, producing a net magnetic field. In unmagnetized materials, the domains are randomly oriented and cancel, so no observable field is created. The figure to the right illustrates these concepts.

The concept of magnetism being entirely due to the motion of charges has been modified significantly in the 20th century, thanks to quantum mechanics. The Bohr model of the atom must be modified to include uncertainty. We can never determine exactly the trajectory of an electron or say for certain where it will be found. The uncertainty principle requires that we instead say only where the electron is most likely to be found. Until we measure the position of the electron, its wave function is spread out over all space, with a higher probability of finding the electron in the classical orbit described by Bohr.

Not all are aligned, but. Like an electric field, a magnetic field may be represented with field lines. In other words, if the applied magnetic field is increasing, the current in the wire will flow in such a way that the magnetic field that it generates around the wire will decrease the applied magnetic field.

The area of the coil can be altered by adjusting the Coil Area slider, thus increasing or decreasing the area inside the coil through which the magnetic field is passing. Notice that moving the slider produces an electric current, as shown by the Ammeter; the direction of the current is both reflected in the ammeter reading positive or negative and in the black arrows that appear.

Another experiment we can perform is to form a wire into a loop and connect the ends to a sensitive current meter, or galvanometer. If we then push a bar magnet through the loop, the needle in the galvanometer will move, indicating an induced current.

However, once we stop the motion of the magnet, the current returns to zero. The field from the magnet will only induce a current when it is increasing or decreasing.

If we pull the magnet back out, it will again induce a current in the wire, but this time it will be in the opposite direction. If we were to put a light bulb in the circuit, it would dissipate electrical energy in the form of light and heat, and we would feel resistance to the motion of the magnet as we moved it in and out of the loop. In order to move the magnet, we have to do work that is equivalent to the energy being used by the light bulb. In yet another experiment, we might construct two wire loops, connect the ends of one to a battery with a switch, and connect the ends of the other loop to a galvanometer.

If we place the two loops close to each other in a face-to-face orientation, and we turn on the power to the first loop, the galvanometer connected to the second loop will indicate an induced current and then quickly return to zero. What is happening here is that the current in the first loop produces a magnetic field, which in turn induces a current in the second loop, but only for an instant when the magnetic field is changing.

When you turn off the switch, the meter will deflect momentarily in the opposite direction. This is further indication that it is the change in the intensity of the magnetic field, and not its strength or motion that induces the current. The explanation for this is that a magnetic field causes electrons in a conductor to move. This motion is what we know as electric current. Eventually, though, the electrons reach a point where they are in equilibrium with the field, at which point they will stop moving.

Then when the field is removed or turned off, the electrons will flow back to their original location, producing a current in the opposite direction.

Unlike a gravitational or electric field, a magnetic dipole field is a more complex 3-dimensional structure that varies in strength and direction according to the location where it is measured, so it requires calculus to describe it fully.

It states that the induced voltage in a circuit is proportional to the rate of change over time of the magnetic flux through that circuit.

In other words, the faster the magnetic field changes, the greater will be the voltage in the circuit. The direction of the change in the magnetic field determines the direction of the current. We can increase the voltage by increasing the number of loops in the circuit. The induced voltage in a coil with two loops will be twice that with one loop, and with three loops it will be triple.

This is why real motors and generators typically have large numbers of coils. In theory, motors and generators are the same. If you turn a motor, it will generate electricity, and applying voltage to a generator, it will cause it to turn. However, most real motors and generators are optimized for only one function.