Magnetism

What is magnetic force a type of?

non-contact force that is strongest at the poles

Define magnetic field

The region around a magnet where a force acts on another magnet or on a magnetic material.

State a factor that affects the strength of the magnetic field

distance from the magnet

list four magnetic materials

iron

steel

nickel

cobalt

describe the difference between a permanent magnet and a induced magnet

Permanent magnets produce their own magnetic field. Induced magnets become a magnet when placed in a magnetic field. However, when removed from the magnetic field, a induced magnet loses most/all of its magnetism quickly.

Explain how a plotting compass can be used to investigate the magnetic field around a magnet

1. Place the magnet on a blank piece of paper.

2. Place the plotting compass at one end of the magnet.

3. Mark on the paper where the needle points.

4. Move the compass to the place you have marked.

5. Repeat this until you have reached the other end of the magnet.

6. Repeat on other length of the magnet (eg. top and then bottom)

Which direction do compass needles always align and why

magnetic north as the earth has a magnetic field. This is due to the iron content in the core.

units for force, magnetic flux density, current and length of wire

N

T

A

m

What is the equation for force?

force = magnetic flux density x current x length of wire

State two factors the strength of the magnetic field depends on

Size of the current and Distance from the wire

State the method that informs you of the direction of the current in a straight wire

right hand grip method/rule

What does your thumb represent in the right hand grip method?

The direction of the current

What does the fingers represent in the right hand grip method?

The direction the field lines should be drawn

What is a solenoid

A solenoid is formed when a long piece of conducting (and insulated) wire is looped into a coiled cylinder

How can you find the north pole of a solenoid?

Using the right hand grip method. hold the solenoid with your right hand and fingers pointing in the direction the current is flowing. Your thumb should point to the north pole.

List four ways you can make the magnetic field around a solenoid/electromagnetic stronger

1. use a larger current

2. Use an iron core

3. Add more coils to the wire

4. Make the coils tighter

What happens to the magnetic field around a straight wire when the current is reversed

The magnetic field is also reversed

What is the motor affect?

If a conductor carrying a current is paced in a magnetic field, the magnet producing the field and the conductor exert a force on each other

State three ways you can increase the force in the motor affect

1. Increasing the size of the current

2. Increasing the length of the conductor in the magnetic field

3. Increasing the flux density

How can you reverse the direction of the force?

By reversing the direction of the current or reversing the direction of the magnetic field

What is the basis of an electric motor?

A coil of wire carrying a current in a magnetic field tends to rotate

How can the direction of the motor be reversed?

by reversing the direction of the current or reversing the direction of the magnetic field

How can the speed of the motor be increased?

By increasing the size of the current or increasing the magnetic field/use a larger magnet

What rule can be used to find the direction of the force?

Flemings left hand rule

What angle do your thumb, first and second finger need to be at in Flemings left hand rule?

90

What does the thumb and two fingers represent in the Flemings left hand rule?

thumb= movement/force

first finger= magentic field

second finger= current

Describe how you would use an iron nail, a length of insulated wire and a cell to make an electromagnet that can be used to pick up some steel paper clips?

1. Wrap the wire around the iron nail.

2. Connect the wire to the power supply (with connecting leads and crocodile clips).

3. Switch on the power supply.

4. Use de-magnetised paper clips and record how many are picked up.

5. The more paperclips suspended, the stronger the magnet is.

6. Change the number of turns on the coil and change the current through the coil.

Why will a motor not work without a commutator?

The commutator ensures that the current stays in the same direction. Also the coil would not be free to spin. This means the coil would remain still and not rotate.

Describe a simple electric motor

A coil of wire is fixed (on a axle). The ends of the wire are connected via a split-ring commutator. To a battery/power supply. The carbon brush contacts at the commutator ensures the current direction in the coil is always the same. The coil is placed between two (flat) magnets with opposite poles facing each other. The coil rotates continuously.