P15 - Electromagnetism Flashcards
What is an alternator?
An alternating current generator
What is a dynamo?
A direct current generator
What is an electromagnet?
An insulated wire wrapped around an iron bar that becomes magnetic when a current flows through the wire
What is electromagnetic induction?
The process of inducing a potential difference using a magnetic field
What is Fleming’s left hand rule?
A rule that gives the direction of the force on a current carrying wire in a magnetic field to the directions of the current and the field
What is the generator effect?
If a conductor is moved through a magnetic field, a potential difference will be induced on the conductor. If this conductor is part of a complete circuit, the induced potential difference causes a current to flow around the circuit.
What is induced magnetism?
Magnetism of an unmagnetized magnetic material by placing it in a magnetic field
What is a magnetic field?
The space around a magnet or a current-carrying wire
What is a magnetic field line?
line in magnetic field along which a magnetic compass points
What is magnetic flux density?
A measure of the strength of the magnetic field defined in terms of the force on a current carrying conductor at right angles to the field lines
What is the motor effect?
When a current is passed along a wire in a magnetic field, and the wire is not parallel to the lines of the magnetic field, a force is exerted on the wire by the magnetic field
What is a solenoid?
A long coil of wire that produces a magnetic field in and around the coil when there is a current in the coil
What is a split-ring commutator?
Metal contacts on the coil of a direct current motor that connects to the rotating coil continually to its electric power supply
What is a step-down transformer?
Electrical device that is used to step down the size of an alternating potential difference
What is a step-up tranformer?
Electrical device that is used to step-up the size of an alternating potential difference
What is a transformer?
Electrical device used to change an alternating voltage
What 3 elements can be permanent magnets?
- Iron
- Cobalt
- Nickel
Describe the magnetic field around a straight current carrying wire?
Circular shape, with field lines closest together nearest the wire as the magnetic field s strongest nearest the wire
How do you find the direction of the magnetic field around a straight current carrying wire?
Use the “right hand grip rule”
What is a wire coiled into a spiral called?
A solenoid
What is the north pole of a magnet?
Where the field lines point outwards
Describe the magnetic field inside a solenoid:
The magnetic field is very strong inside a solenoid. The field lines are parallel to the axis of the solenoid, and they are uniform (in the same direction).
Describe the magnetic field outside a solenoid:
the magnetic field lines bend from the north end of the solenoid to the south end of the solenoid. The magnetic field lines from a complete loop as they pass through the inside of the solenoid
How do magnetic field lines represent the strength of a magnetic field?
If the magnetic field lines are closer together then the magnetic field is stronger. But if the magnetic field lines are further apart then the magnetic field is weaker
How do you make the magnetic field of a solenoid stronger?
- Increase the current
- Add more turns to the coil
- Add an iron core to create an electromagnet
What type of magnet is an electromagnet?
Temporary Magnet
How does an electromagnet work?
When a current is passed along the wire, a magnetic field is created around the wire. Because of this, the magnetic fields of the wire magnetise the iron core
How does an electromagnet pick up an unmagnetized magnetic material, such as iron?
The electromagnet’s pole induces the opposite pole on the material, therefore they are opposite poles and attract
What is the south pole of a magnet?
Where the field lines point in
Why are electromagnets useful?
- They can be turned on and off
- The direction of the magnetic field can be reversed
- They are much stronger than regular permanent magnets
What are 4 ways electromagnets are used in devices?
- Scrap yard cranes
- Circuit breaker
- Electric Bell
- Relay
Describe how an electromagnet is used in scrap yards?
A large electromagnet is attached to a crane. When a current is run through the wire, the electromagnet is turned on and is used to pick up and move heavy pieces of scrap metal. When the current is switched off, the electromagnet turns off and the scrap metal falls off the electromagnet
How is an electromagnet used in a circuit breaker?
A circuit breaker is a switch in series with an electromagnet. The switch is held close (allowing a current to flow) by a spring. When the current is too large, the strength of the electromagnet is increased and pulls open thee switch. The switch remains open until it is reset manually
Describe how an electric bell works:
When an electric bell is pushed, the circuit is completed causing the electromagnet to attract the iron armature, which hits a bell. Because the iron armature is pulled away, the metal strip is pulled away from the contact, causing the make-and-break switch to be broken, the circuit is no longer completed and the electromagnet loses its magnetism and the armature springs back, this causes the make and break switch to be complete, causing cycle to repeat rapidly
What is a relay?
A device used to switch an electrical machine with a large current on or off with a small current
Describe how a relay works:
A small current is ran through the coil of the electromagnet causing the electromagnet to turn on, this pulls the iron armature onto the electromagnet. As a result the contacts are pushed together and the switch gap is closed and the machine is switched on. in this way a small current is used to switch on a machine with a much bigger current.
What is induced magnetism?
An unmagnetized magnetic material becomes magnetised when in contact with a magnetic field
How can you increase the strength of the force produced in the motor effect?
- Increasing the current
- Increasing the magnetic field strength
- Increasing the length of the wire