Unit 7 Summary

MAGNETISM

àThe source of magnetism is moving charges

àMagnetic force is the force due to the motion of charged particles

àMagnets are clouds of magnetic charges

In order for a force to be felt, the magnetic field must be perpendicular to the movement of electrons

For example, cosmic rays are felt at the poles because charges are moving perpendicular to the magnetic field, and parallel at the equator.

Magnetic field lines of a magnet

àCompasses are magnets that are free to respond to the magnetic field of the earth

Why does a paperclip stick to a magnet?

The domain of the magnet is a cluster of spinning electrons. The magnet has a magnetic field, and the paper clip has a random domain. When the two come in contact, the domain of the clip align and match the magnetic field.

Now the paperclip has a north and south pole. The opposite poles of the clip and magnet attract each other, so it sticks

Demagnetized vs. Magnetized domains

MOTORS

All motors depend on a magnet, and a current carrying wire. The wire must feel a force in the magnetic field and cause a torque in order for it to spin. Remember, that in order for the wire to feel a force, it must be moving perpendicular to the magnetic field. In a motor, electrical energy is converted to mechanical energy.

ELECTROMAGNETIC INDUCTION

Electromagnetic induction is a method used to induce a voltage by changing an object’s magnetic field, and hence inducing a current.

More specifically, when magnets revolve around a series of wire coils, the magnetic field is changed in order to induce the voltage and current. The current is typically used as a signal or message, which operates everyday objects.

Every time I played an electric guitar, I didn’t realize that the sound was produced through electromagnetic induction. There are metal coils underneath the pickups of the guitar, fixed with small pickup magnets. When you pluck a metal string, you change the magnetic field with the vibrations. Since the magnetic field has changed, both a voltage and a current have been induced. The current sends a signal to the amplifier (connected to pickups) and then releases sound.

(P1)

These signals can also be used in metal detectors, stop light signs, and credit card machines. I really enjoyed learning about this because I was able to relate it to my everyday life so easily, given that I shop too much and play guitar J

GENERATORS

A generator is a rotating coil within a stationary magnetic field. They essentially depend on a magnet to change the magnetic field. The way this works is by sticking a magnet in and out of a wire loop, which alternates the direction of the voltage.

TRANSFORMERS

The objective of a transformer is to change the voltage of a system. This works by changing the magnetic field of the primary (AC) current which will change the magnetic field of the secondary (DC). It is important for the loops of the primary to have alternating current, that way the magnetic field has the opportunity to change.