Grade 11 Physics: Jan. 7

Here's the schedule for the remainder of the term:

Magnetism

Magnetism is an intrinsic property of some particles, like charge or mass.

Magnets exert forces on other magnets.

Like poles repel N-N or S-S

Unlike poles attract N-S or S-N

Permanent Magnets

Have a North and South pole.

We draw magnetic field lines to show the direction that a compass would point: away from the N and towards S.

- field lines never cross.

- lines get further apart as they leave the magnet.

Poles only exist in pairs. No such thing as a “monopole”. If you break a magnet in half, you get two magnets.

The Earth has a magnetic field that protects us from charged particles coming from the sun.

When these particles hit the Earth's atmosphere (at the poles) they create auroras.

Magnetic fields are measured in Teslas.

Ferromagnetic Materials

Some materials, like iron, are made up of magnetic domains. Many domains point in different directions cancel each other out.

An external magnetic field can line up the domains and make the material behave like a permanent magnet. (temperature also affects domains)

Electromagnets

When current passes through a conductor, magnetic fields form. We use the right-hand-rule to predict the direction of the field.

Ex: Current on a wire.

Thumb points in direction of I.

Fingers show direction of B (magnetic field).

At this point, it is useful to use these symbols to draw vectors in 3D:

Ex: Wires coiled into loops can create a magnetic field that looks exactly like a permanent bar magnet. This is called a solenoid.

Right-hand-rule for solenoids.

- wrap your fingers in the direction of the current. Your thumb will point to the N.

Electromagnets are useful for many applications.

Handout