magnetism

What is a magnetic field?

The region where magnetic materials experience a force.

What do magnetic field lines show?

The size and direction of magnetic fields.

They always go from north to south.

What is a uniform magnetic field?

-When the magnetic field is the same distance apart and parallel.

-When the north and south poles of two permanent bar magnets are set beside each other.

What is electromagnetism?

When an electric current flows through a magnetic material it produces a magnetic field around it.

What does magnetically soft mean?

The material is easily magnetised and demagnetised

What does magnetically hard mean?

The material is difficult to magnetise and demagnetise

How do you make an electromagnet stronger?

-Add more turns to the coil.

-Increase the current through a coil.

-Wrap a coil around a soft iron core.

What does the right hand rule show?

thumb is current, fingers are field. hold as if thumbs up

What is the motor effect?

-When a current-carrying wire is placed between magnetic poles, the two magnetic fields affect one another and a force is produced on the wire causing it to move.

Why does the motor effect happen?

-The electrons in the current that are moving through a magnetic field will experience a force, as long as they're not moving parallel to the field lines.

What does Fleming's left hand rule show?

-Thumb=direction of force.

-Index finger=magnetic field.

-Middle finger=current.

Describe the electric motor.

-A coil of wire that is free to rotate is placed between two opposite poles.

-When a current flows through the coil it experiences a force and moves.

-Because the coil is on a spindle and forces act one up and one down, it rotates.

What is the function of the split-ring commutator in an electric motor?

-Swaps the contacts every half-turn to keep the motor rotating in the same direction.

How can the speed of the electric motor be increased?

-Adding more turns to the coil.

-Increasing the current.

-Stronger magnetic field.

-A soft iron core.

How does a loudspeaker function?

-A.C signals from an amplifier are fed to a coil of wire in the speaker, which is wrapped around the base of a cone.

-The coil is surrounded by a permanent magnet, so the A.C signals cause a force on the coil and make it move back and forth.

-These movements make the cone vibrate and create a sound wave

What is electromagnetic induction?

-The creation of a voltage in a wire which is experiencing a change in magnetic field.

What is the dynamo effect?

-Using electromagnetic induction to transform kinetic energy into electrical energy.

How do you demonstrate electromagnetic induction?

-Move a magnetic field (bar magnet) through an electrical conductor.

Describe how a generator functions.

-A coil rotates in a magnetic field.

-As the coil spins, a current is induced in the coil.

-The current changes direction every half-turn.

-The slip rings and brushes stop the contacts swapping every half turn.

-Produce A.C voltage.

Describe how a transformer functions.

-Change the size of the voltage of an alternating current.

-When an A.C voltage is applied across the primary coil, the soft iron core magnetises and demagnetises quickly.

-The secondary coil is cutting magnetic field lines.

-This induces an A.C voltage on the secondary coil.

What is a step-up transformer?

-Increases the voltage.

-More coils on the secondary coil.

What is a step-down transformer?

-Decreases the voltage.

-Fewer coils on the secondary coil.

Describe how the electric bell functions.

-When the switch is pressed, the circuit is complete and the current flows.

-The electromagnet has become magnetised and attracts the soft iron armature which will cause the hammer to strike the bell.

-At the same time a gap is created at the contact screw and the circuit is incomplete.

Describe how a circuit breaker functions.

-If the current is too high the electromagnet becomes strong enough to pull the iron lever so that the contacts open and the circuit breaks.

-Once the circuit has been fixed the lever is repositioned by pressing the rest button.

Describe how a relay switch functions.

-When the switch is closed, the circuit is complete and the current flows around the circuit.

-As the current passes through the coil and the electromagnet becomes magnetised it attracts the iron armature which is pivoted so the lower end pushes the contacts of the second circuit together.

What is a magnetic field?

The region where magnetic materials experience a force.