Magnetism And Electromagnetism Flashcards
What are magnetic materials?
Materials that magnets are able to attract to
E.G Iron, nickel and cobalt
What are non-magnetic materials?
Materials that magnets cannot attract to
E.G plastic, wool, paper and rubber
What are the strongest parts of a magnet?
The poles
What are permanent magnets?
Are magnets made from magnetically hard material e.g steel (that is what makes it permanent). A magnetically hard materials retains its magnetism once it has been magnetised
What are temporary magnets?
Is made of magnetically soft material e.g. Iron and would not be suitable for a permanent magnet. Magnetically soft materials lose their magnetism easily and are therefore useful as temporary magnets.
How can magnetism be induced?
Magnetism can be induced in a magnetic material by leaving it in a magnetic field.
What is electromagnetism?
When current flows through a wire a magnetic field is created around the wire. Right Hand Rule
How can the strength of the magnetic field around a current carrying wire be increased?
- Increasing current in the wire
- Wrapping the wire into a coil or solenoid (a solenoid is a long coil)
- If the direction of the current flowing through the solenoid is reversed, so too are the position of the poles.
How can the strength of the field around a solenoid be increased?
- Increasing the current flowing through the solenoid
- Increasing the number of turns on the solenoid
- Wrapping the solenoid around a magnetically soft core such as iron, this combination of soft iron core and solenoid is often referred to as an ELECTROMAGNET.
Using electromagnets: Electric bell
- Bell pushed pressed the circuit is complete and current flows
- Soft iron core of electromagnet become magnetised and attracts the iron armature.
- When the armature moves the hammer strikes the bell and at the same time a gap is created at the contact screw.
- The circuit is incomplete and current stops flowing.
- The electromagnet is now turned off so the springs’s armature returns to its original position.
- The circuit is again complete and the whole process begins again.
Using electromagnets: circuit breaker
- If the current is too high the electromagnet becomes strong enough to pull the iron catch out of position so that the contacts open and the circuit breaks.
- Once the problem in the circuit has been corrected the catch is repositioned by pressing the reset button.
Using electromagnets: relay switch
A relay switch uses a small current in one circuit to turn on a second circuit that may be carrying a much larger current.
1. When switch S is closed a small current flows around the circuit on the left
2. As current passes through the coil C, the soft iron core becomes magnetised and attracts the iron armature.
3. Because the armature is pivoted at X, its lower end Y pushes the contacts of the second circuit together.
3. The circuit is complete and current flows without the user coming into contact with the potentially more dangerous circuit.
4. If the switch S is opened the electromagnet is turned off, the iron armature moves back to its original position and the contacts spring apart, turning the right-hand circuit off.
E.G used in car ignition circuits.
Why are relay switches used?
When large currents flow in a circuit there is always the danger of the user receiving a severe electric shock, even turning the switch on and off can be hazardous.
What is a magnetic field line?
Are used to show the size and direction of magnetic fields, they always point NORTH to SOUTH
What happens when you place the north and south poles of two permanent magnets near each other?
Creates a uniform field between the two magnets
