What do magnets produce?
A magnetic field
How many poles do magnets have?
2 North and South
What is a magnetic field?
A region where magnetic materials (e.g. iron) experience a force
What do magnetic field lines do?
Show the size and direction of the magnetic fields, They always point from NORTH –> SOUTH
What is a magnetically soft material?
A material that can become an induced (or temporary) magnet when it is in a magnetic field. It stops acting like a magnet relatively quickly.
What is a magnetically hard material?
A material (e.g. steel) that will remain magnetised until demagnetised. It will attract or repel other magnets.
How can a magnet be demagnetised?
By disrupting the domains by heat or force (beating the magnet)
What is a solenoid
A coil of wire that is part of an electric circuit. While current is flowing the coil has a magnetic field around it. The more coils there are the stronger the magnetic field.
What is an electromagnet?
A solenoid with an iron core (magnetically soft), which only has a magnetic field when the current is flowing.
What is the benefit of having an electromagnet?
Being able to turn the magnet on or off.
What does an electric current in a conductor produce?
A magnetic field.
When might an electromagnet be used in industry?
At a recycling centre to be able to lift and then drop materials - such as old cars.
What is the right-hand grip rule?
Applies to magnetic fields near a straight wire The thumb points in the direction of the current and the fingers curl in the direction of the magnetic field lines.
What happens to the magnetic field if the electric current is increased?
It gets STRONGER
What shape is the magnetic field around a straight wire?
concentric circles around the straight wire
What shape is the magnetic field around a flat circular coil?
Similar to that of a bar magnet - concentric ellipses (stretched circles) around the coil.
What is the magnetic field like inside a current-carrying solenoid?
Strong and uniform
What is the magnetic field like outside a current-carrying solenoid?
Like the field on a bar magnet. The ends of the solenoid act like the north and south poles on a magnet. This is called an electromagnet.
Why is iron used in transformers?
Because it can magnetise and demagnetise quickly mains electricity needs to do this 50 times a second = 50Hz
When can the motor effect happen?
When a current carrying wire is put in a magnetic field.
What happens when a current-carrying wire is put between magnetic poles?
The 2 magnetic fields affect one another causing a force on the wire. This causes the wire to move. this is called the motor effect
At what angle to the magnetic field does the wire have to be to feel the full force?
What happens if the wire runs along the magnetic field?
No force is felt
What happens to the strength (magnitude) of the force when the magnetic field increases?
What happens to the strength (magnitude) of the force when the current increases?
What happens if the current or magnetic field is reversed?
The direction of the force is also reversed.
Which rule tells you which way a force acts in the motor effect?
Flemmings left-hand rule. thuMb = Motion First Finger = Field seCond finger = Current
What 4 factors speed up a simple DC electric motor?
- more current 2. more turns on the coil 3. stronger magnetic field 4. soft iron core in the coil
Explain how a simple DC motor works
- Forces act on the 2 side arms of the coil - 1 up and 1 down
- the coil is on a spindle so it rotates
- The split ring commutator swaps the contact every half turn to keep the motor rotating in the same direction
- The sirection of the motor is reversed by swapping the polarity of the d.c. supply or by swapping the poles over
- The speed is increased by adding more turns to the coil, or by increasing the current or by increasing the strength of the magnetic field ir by adding a soft iron core
- You can use Flemmings left hand rule to work out which way the coil will turn
How do loud speakers work?
using the motor effect
- AC electrical sugnals from an amplifier are fed to a coil of wire in the speaker
- The coil is surrounded by a permanent magnet -> the a.c. signals cause a force on the coil and make it move back and forth
- These movements make the cone vibrate and this creates sounds.
What is EM or electromagnetic induction?
The creation of voltage in a wire which is experiencing a change in magnetic field