Magnetic flux is a measure of the total magnetic field which passes through a given surface. It depends on the area of the surface, the strength of the magnetic field where the surface is located, and the angle at which the magnetic field hits the surface. If you have a surface such as a metal sheet, it would make sense that the total magnetic field passing through would be bigger if the sheet were bigger, or if the field were stronger.

The magnetic flux of a solenoid is proportional to the amount of coils there are: if there are more coils, the flux is greater. In this case, the only thing that could change the flux would be a greater magnetic field, so if the flux is greater, the magnetic field must also be stronger. Therefore, the strength of the magnetic field is determined by how many “ampere turns“ there are in the coil: with more turns, the stronger the magnetic field.

If you were to remove the current from the wire the magnetic field would be lost. However, by moving a magnetic cylinder back and forth through the coil, a current is created. This process is called electromagnetic induction. The current is induced into the coil by the movement of magnetic flux. This current therefore creates a voltage, creating electricity. This is the general process behind generators and transformers.

The change in flux created what was called the ElectroMotive Force, or EMF for short which induces a voltage. The current was measured with what is called a galvanometer.

When the magnet was moved towards the coil, the galvanometer will deflect in one direction. When moved away, or moved towards with the opposite pole, the galvanometer will deflect in the other direction. When held stationary, the galvanometer will point to 0, as there is no movement of the magnetic field. Also, the faster the motion, the greater current was induced into the wire.

This idea created Faraday’s law, which states that “a voltage is induced in a circuit whenever relative motion exists between a conductor and a magnetic field and that the magnitude of this voltage is proportional to the rate of change of the flux,” basically saying that magnetic field movement can induce a voltage in a closed circuit.

However, this is not completely sustainable, Lenz’s law states that the induced current will always oppose the motion, or change what started the induced current. This idea relates to Newton’s third law, where every action has an equal but opposite reaction, as well as the law of conservation of energy. The magnet will be opposed by the current that it created.