Electromagnetic Induction
ELECTROMAGNETIC INDUCTION HOW A CHANGING CURRENT CAN BE USED TO INDUCE CURRENT IN ANOTHER CIRCUIT.
REVIEW • If you looked through the first resource for this section of the playlist (CK12), then you should have seen the following information:
• Electromagnetic Induction is when electric current is created by a magnetic field
• Electric current is produced when a nearby magnetic field is CHANGING.
• The conductor (length or coil of wire) needs to be part of a closed circuit in order for electromagnetic induction to work.
• These are a few ways in which current can be produced by electromagnetic induction:
• Moving a magnet near a coil of wire in a closed circuit. • Moving a coil of wire in a closed circuit near a magnet.
ANOTHER WAY THAT ELECTROMAGNETIC INDUCTION CAN WORK. • If you have one coil of wire that is
Battery
Coils of wire
connected to a battery (an electromagnet) near another closed circuit with no battery, moving either of these circuits will generate current in the second circuit.
• The second circuit can just be a piece of wire with the two ends connected to each other.
Ammeter (measures how much current runs through a circuit. Does NOT provide any power to the circuit)
CHECK FOR UNDERSTANDING • Which of the following actions will cause a current to flow in circuit 2, so that the ammeter shows a value that isn’t zero? (check all that apply)
1) Moving Circuit 1 towards Circuit 2 2) Moving Circuit 1 away from Circuit 2 3) Moving Circuit 2 towards or away from Circuit 1
Circuit1
Circuit2
CHECK FOR UNDERSTANDING (ANSWER) • Answer: ALL OF THEM!!! 1) Moving Circuit 1 towards Circuit 2:
- This will create current in Circuit 2 because as long as either one of the circuits moves, the magnetic field will change.
2) Moving Circuit 1 away from Circuit 2:
- Same thing! One of the circuits is still moving. It doesn’t matter what direction it moves in.
3) Moving Circuit 2 towards or away from Circuit 1: -This one works as well for the same reasons. It doesn’t matter which circuit moves as long as one of them moves, the magnetic field changes, which causes current to flow through circuit 2.
YET ANOTHER WAY THAT ELECTROMAGNETIC INDUCTION CAN WORK Battery
• Picture the same situation from
Switch
Coils of wire
the last slide in your mind (2 closed circuits are near each other, one has a battery, one doesn’t)
• Add a switch to the circuit that has a battery, like you see in the picture to the right
Ammeter (measures Current)
YET ANOTHER WAY THAT ELECTROMAGNETIC INDUCTION CAN WORK (CONTINUED) When the switch in the circuit with a battery is opened or closed, current will run through the other circuit, but ONLY FOR A MOMENT (LESS THAN A SECOND)!!!
• This is because it is only at the very moment that the switch is opened or closed that the magnetic field is changing.
CHECK FOR UNDERSTANDING • What would happen to the ammeter in Circuit 2 if the switch in Circuit 1 was opened (after being closed for some period of time)?
Circuit1
Circuit2
1) The ammeter will show a constant, steady current.
2) The ammeter will show a current at the moment the switch is opened, then fall back to zero.
3) The ammeter won’t show any current.
Ammeter
CHECK FOR UNDERSTANDING (ANSWER) • Answer: 2) The meter will show a current at the moment the switch is opened, then fall back to zero. • This answer is correct because it is only at the moment that the switch is opened or closed that a changing magnetic field is created. A changing magnetic field is required to induce current in the other circuit.
• Here’s why answers 1 and 3 are incorrect: 1) The meter will show a constant, steady current
- The magnetic field is only changing at the moment the switch is opened. After that moment has passed, the magnetic field isn’t changing, so there wouldn’t be any current in Circuit 2 anymore 2) The ammeter won’t show any current.
- The magnetic field is changing at the moment the switch is opened, so there would be a current shown only at this brief instant.
SO WHAT DID WE LEARN? (SUMMARY) • Electromagnetic Induction happens whenever a magnetic field is changing near a closed circuit with no battery
• There are two new ways to create a changing magnetic field that we learned
• Move a closed circuit that is connected to a voltage source (battery) • Open or close a switch in a circuit with a voltage source (the magnetic field will only be changing at the very moment that the switch is opened or closed).
• Since a changing magnetic field is created, this will cause electric current to flow in a nearby closed circuit, even when there is no battery!!!
REVIEW • If you looked through the first resource for this section of the playlist (CK12), then you should have seen the following information:
• Electromagnetic Induction is when electric current is created by a magnetic field
• Electric current is produced when a nearby magnetic field is CHANGING.
• The conductor (length or coil of wire) needs to be part of a closed circuit in order for electromagnetic induction to work.
• These are a few ways in which current can be produced by electromagnetic induction:
• Moving a magnet near a coil of wire in a closed circuit. • Moving a coil of wire in a closed circuit near a magnet.
ANOTHER WAY THAT ELECTROMAGNETIC INDUCTION CAN WORK. • If you have one coil of wire that is
Battery
Coils of wire
connected to a battery (an electromagnet) near another closed circuit with no battery, moving either of these circuits will generate current in the second circuit.
• The second circuit can just be a piece of wire with the two ends connected to each other.
Ammeter (measures how much current runs through a circuit. Does NOT provide any power to the circuit)
CHECK FOR UNDERSTANDING • Which of the following actions will cause a current to flow in circuit 2, so that the ammeter shows a value that isn’t zero? (check all that apply)
1) Moving Circuit 1 towards Circuit 2 2) Moving Circuit 1 away from Circuit 2 3) Moving Circuit 2 towards or away from Circuit 1
Circuit1
Circuit2
CHECK FOR UNDERSTANDING (ANSWER) • Answer: ALL OF THEM!!! 1) Moving Circuit 1 towards Circuit 2:
- This will create current in Circuit 2 because as long as either one of the circuits moves, the magnetic field will change.
2) Moving Circuit 1 away from Circuit 2:
- Same thing! One of the circuits is still moving. It doesn’t matter what direction it moves in.
3) Moving Circuit 2 towards or away from Circuit 1: -This one works as well for the same reasons. It doesn’t matter which circuit moves as long as one of them moves, the magnetic field changes, which causes current to flow through circuit 2.
YET ANOTHER WAY THAT ELECTROMAGNETIC INDUCTION CAN WORK Battery
• Picture the same situation from
Switch
Coils of wire
the last slide in your mind (2 closed circuits are near each other, one has a battery, one doesn’t)
• Add a switch to the circuit that has a battery, like you see in the picture to the right
Ammeter (measures Current)
YET ANOTHER WAY THAT ELECTROMAGNETIC INDUCTION CAN WORK (CONTINUED) When the switch in the circuit with a battery is opened or closed, current will run through the other circuit, but ONLY FOR A MOMENT (LESS THAN A SECOND)!!!
• This is because it is only at the very moment that the switch is opened or closed that the magnetic field is changing.
CHECK FOR UNDERSTANDING • What would happen to the ammeter in Circuit 2 if the switch in Circuit 1 was opened (after being closed for some period of time)?
Circuit1
Circuit2
1) The ammeter will show a constant, steady current.
2) The ammeter will show a current at the moment the switch is opened, then fall back to zero.
3) The ammeter won’t show any current.
Ammeter
CHECK FOR UNDERSTANDING (ANSWER) • Answer: 2) The meter will show a current at the moment the switch is opened, then fall back to zero. • This answer is correct because it is only at the moment that the switch is opened or closed that a changing magnetic field is created. A changing magnetic field is required to induce current in the other circuit.
• Here’s why answers 1 and 3 are incorrect: 1) The meter will show a constant, steady current
- The magnetic field is only changing at the moment the switch is opened. After that moment has passed, the magnetic field isn’t changing, so there wouldn’t be any current in Circuit 2 anymore 2) The ammeter won’t show any current.
- The magnetic field is changing at the moment the switch is opened, so there would be a current shown only at this brief instant.
SO WHAT DID WE LEARN? (SUMMARY) • Electromagnetic Induction happens whenever a magnetic field is changing near a closed circuit with no battery
• There are two new ways to create a changing magnetic field that we learned
• Move a closed circuit that is connected to a voltage source (battery) • Open or close a switch in a circuit with a voltage source (the magnetic field will only be changing at the very moment that the switch is opened or closed).
• Since a changing magnetic field is created, this will cause electric current to flow in a nearby closed circuit, even when there is no battery!!!
