P7-Magnetism and Electromagnetism

What is a magnetic field

A magnetic field is a region where other magnets or magnetic materials experience a force

What are magnetic materials?

Magnetic materials include iron, steel, nickel and cobalt

How can you show a magnetic field

You can show a magnetic field by drawing magnetic field lines

Where do the lines go on magnetic field lines?

The lines go from North to South

What do magnetic field lines show?

They show which way a force would act on a north pole if it was put at that point in the field

Where is the magnetic field strongest?

The magnetic field is strongest at the poles of a magnet (so also the magnetic forces)

What is the force between a magnet and a magnetic material? (permanent and induced)

The force between a magnet and a magnetic material is always attractive, no matter the pole

What happens if two poles of a magnet are put near eachother?

If two poles of a magnet are put near each other, they will exert a force on each other

What is a compass made of

Inside a compass is a tiny bar magnet

What does a compass do?

-The compass points in the direction of the magnetic field it is in

-This is because the N pole of the magnet is attracted to the S pole of any other magnet it's near

How can you picture a magnetic field?

You can move a compass around a magnet and trace its position on a piece of paper to build up a picture of what the magnetic field looks like

Where do compasses point?

-Compasses point North (when not near a magnet) because the Earth generates its own magnetic field

-This shows the inside core of the Earth must be magnetic

What are permanent magnets?

Permanent magnets produce their own magnetic field

What are induced magnets?

Induced magnets are magnetic materials that turn into a magnet when put into a magnetic field

What happens when you take away the magnetic field from an induced magnet?

When you take away the magnetic field, induced magnets quickly lose their magnetism (or most of it) and stop producing a magnetic field

What happens when a current flows through a wire?

When a current flows through a wire, a magnetic field is created around the wire

What is the field around a wire made up of?

The field is made up of concentric circles perpendicular to the wire, with the wire in the centre

How can you change the direction of the magnetic field on a wire?

Changing the direction of the current changes the direction of the magnetic field

How can you work out which way the magnetic field of a wire goes?

-The right-hand thumb rule

-Point your thumb in the direction of current and curl fingers

-The direction of your fingers is the direction of the field

How can you increase the field strength around a wire?

The larger the current through the wire, or the closer to the wire you are, the stronger the field is

What is a solenoid?

You can increase the strength of the magnetic field that a wire produces by wrapping the wire into a coil (solenoid)

Why can you increase the magnetic field of a wire with a solenoid?

-This happens because the field lines around each loop of wire line up with earchother

-This results in lots of field lines pointing in the same direction that are very close to each other

What is the magnetic field like inside/outside a solenoid?

-The magnetic field inside a solenoid is strong and uniform (same strength and direction at every point in that region)

-Outside the coil, the magnetic field is like the one around a bar magnet

What is an electromagnet?

-You can increase the field strenth of a solenoid by putting a block of iron in the centre of the coil

-This iron core becomes an induced magnet when the current flows

-An electromagnet is a magnet whose magnetic field can be turned on and off with an electric current

What can electromagnets be used in?

-Electromagnets are used in some cranes to attract and pick up things made from magnetic materials

-Using an electromagnet means the magnet can be switched on when you want to pick stuff up, then switched off when you want to drop it

-Electromagnets can be used in circuits to act a switches

What is the motor affect?

-When a current-carrying wire is put between magnetic poles, the magnetic field around the wire interact with the magnetic filed it has been placed in

-This causes the magnet and the conductor to exert a force on each other

-This can cause the wire to move

What will the angles in the motor affect effect?

-To experience the full force, the wire has to be at 90' to the magnetic field

-If the wire runs parallel to the magnetic field, it wont experience any force at all

-At angles in between, it'll feel some force

What happens when you apply a current to a set of rails in a horseshoe magnet?

-A bar is placed on the rails, which completes the circuit

-This generates a force that rolls the bar along the rails

What is the magnetic flux density?

How many field (flux) lines there are in a region, showing the strength of the magnetic field

When can you use "F= BIl"?

When the current is at 90' to the magnetic field, you can use "F = BIl"

How can you work out which way a force is acting (field/current/force)?

-Fleming's left hand rule

-First finger points in the direction of the Field

-SeCond finger in the direction of the Current

-ThuMb in the direction of the force (Motion)