Demonstrating induction
- Electromagnetic induction is used in:
- electrical generators which convert mechanical energy to electrical energy
- transformers which are used in electrical power transmission
- The phenomenon of electromagnetic induction can be demonstrated using
- a magnet and a coil
- a wire and a U-shaped magnet
Experiment 1: moving a magnet through a coil
- When a coil is connected to a sensitive voltmeter, a bar magnet can be moved in and out of the coil to induce an e.m.f.
An e.m.f. is induced in a coil when a bar magnet is moved through it. This can be seen by connecting the coil to a voltmeter
- The expected results are...
1. When the bar magnet is stationary, the voltmeter shows a zero reading
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- When the bar magnet is held still inside, or outside, the coil, there is no cutting of magnetic field lines
- As a result, no e.m.f. is induced in the coil
2. When the bar magnet is moved inside the coil, there is a reading on the voltmeter
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- As the bar magnet moves, its magnetic field lines are cut by the coil
- This induces an e.m.f. within the coil, shown momentarily by the reading on the voltmeter
3. When the bar magnet is moved back out of the coil, there is a reading on the voltmeter with the opposite sign
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- As the magnet changes direction, the direction of the current changes
- An e.m.f. is induced in the opposite direction, shown momentarily by the reading on the voltmeter with the opposite sign
An e.m.f. is induced only when the bar magnet is moving through the coil
- Factors that will increase the induced e.m.f. are:
- moving the magnet faster through the coil
- adding more turns to the coil
- increasing the strength of the bar magnet
Experiment 2: moving a wire through a magnet
- When a long wire is connected to a voltmeter and moved between two magnets, an e.m.f. is induced
- The pattern of a magnetic field in a wire can be investigated using this setup
- Note: there is no current flowing through the wire to start with
An e.m.f. is induced in a wire when it is moved between magnetic poles. This can be seen by connecting the wire to a voltmeter
- The expected results are...
1. When the wire is stationary, the voltmeter shows a zero reading
-
- When there is no relative motion between the wire and the magnetic field, no field lines are cut
- As a result, no e.m.f. is induced in the wire
2. As the wire is moved between the magnetic poles, there is a reading on the voltmeter
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- As the wire moves, it cuts the magnetic field lines of the magnet
- This induces an e.m.f. in the wire, shown momentarily by the reading on the voltmeter
3. When the wire is moved back out of the magnet, there is a reading on the voltmeter with the opposite sign
-
- As the wire changes direction, the direction of the current changes
- An e.m.f. is induced in the opposite direction, shown momentarily by the reading on the voltmeter with the opposite sign
- Factors that will increase the induced e.m.f. are:
- increasing the length of the wire
- moving the wire between the magnets faster
- increasing the strength of the magnets