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Using magnetism to induce a current
KEy question:
KEy question:
How do we 'make' electricity?
How do we 'make' electricity?
Task 1 - recap questions
Task 1 - recap questions
Do the questions on task 1 of the companion sheet.
Can you remember the formula that links the current in a conductor, Magnetic flux density, length of wire and force produced?
Task 2 - Faraday puzzle
Task 2 - Faraday puzzle
Watch the video
Enjoy the demonstrations in class
Read the sections below on Generators and induction.
Then, on your companion sheet, summarise Induction and the generator effect.
A Summary of Generators and Induction
A Summary of Generators and Induction
Magnets
Magnets
If we consider a simple magnet it has magnetic field lines that go from the north end to the south end – like in the diagram below, Fig 1
Induction
Induction
If one of these field lines moves through an area where we have an electrical conductor (perhaps a piece of wire) then we induce a voltage (strictly speaking this is called a potential difference). If the conductor is part of a complete circuit then this allows a current to flow.
The reason for this is rather complicated! Charged particles, like electrons, experience a force due to a magnetic field which causes them to move – you will learn more about this effect at A level physics.
We can say If an electrical conductor ‘cuts’ through magnetic field lines, an electrical potential difference is induced across the ends of the conductor.
If the wire is part of a complete circuit, a current is induced in the wire.
If we hold a magnet stationary outside a coil of wire, a voltmeter would register a reading of zero volts. This is because no field lines are being cut.
If we were to then move the magnet into the coil of wire at a steady speed we would induce a voltage (and also induce a current in a complete circuit). This voltage would register on the voltmeter – perhaps +6.0 volts. This is because the magnetic field lines are moving across the coils of wire. They are being ‘cut’.
If we were to now move the magnet back out at the same speed then we would see the reading on the voltmeter would change direction – this time to -6.0 volts. We are still inducing a voltage but this time in the opposite direction.
It does not matter if we move the magnet into the coil, or if we move the coil over the magnet. As long as one is moving relative to the other we induce a voltage. This is called the generator effect.
It does not matter if we move the magnet into the coil, or if we move the coil over the magnet. As long as one is moving relative to the other we induce a voltage. This is called the generator effect.
Summary
Summary
If a magnet is moved into a coil of wire, an electrical potential difference is induced across the ends of the coil.
If the direction of motion, or the polarity of the magnet, is reversed, the direction of the induced potential difference and the induced current is reversed.
The generator effect also occurs if the magnetic field is stationary and the coil is moved – as long as one is moving relative to the other.
Task 3 - How do we generate electricity
Task 3 - How do we generate electricity
Watch the video and read thei information below.
Then complete task 3 on the companion sheet.
Diagram of a generator
Diagram of a generator
Magnet:
This provides the magnetic field. In the generator above the field lines go from the north end to the south end.
Coil of Wire
This is the conductor that ‘cuts’ the field lines. Something turns this: perhaps a turbine in a power station or a scientisfrantically turning a handle.
Axle:
This allows the coils of wire to rotate: The spindle to allow circular motion.
Slip Rings:
There are two of these: one is attached to each end of the coil. In the diagram above the yellow coloured ring iattached to the yellow end of the coil only, the green ring is attached only to the green end of the coil.
Brushes
These are often made or carbon (because it conducts electricity and has low friction). They make a connection between the slip rings and wires in the circuit to allow current to flow. They slide over the surface of the ring, a bit like a brush sweeping a floor.
Task 4 - Push for grade 9
Task 4 - Push for grade 9
Microphones, Speakers and ....Pickups!
Look at the information above -think
How do the Pickups on an electric guitar work?
Complete the task on your companion sheet
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