The Generator Principle
Faraday's law, electromagnetic induction, and generating electric current
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This is an awesome
Faraday's
G) Generator Principle - Electromagnetic Induction
Meet Michael Faraday — the physicist behind electromagnetic induction
1831 - Michael Faraday discovered that current and voltage can be induced when a conductor (closed loop) moves within a magnetic field.
Engraving by John Cochran (1821-1865) of a portrait of Michael Faraday � Copyright 1997,
http://www.walter-fendt.de/ph11e/ (Note: 3 dimensional view)
Wire is perpendicular to page If this wire is moved up or down (perpendicular to the field), maximum current (and V) will be generated.
Moved left or right (parallel
to the field),
Toward which point should the wire be moved to induce the maximum electric potential? (voltage)
Point 1, perpendicular to field
The wire movement determines
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movie is part of the collection: Creative Commons license: Public Domain
How to find the direction of current
Step 1: flux lines - Out of N into S Step 2: 4 fingers follow flux lines Step 3: Thumb follows movement of wire (Given) Step 4: Palm shows Push on electrons - The current direction
Ex) If the wire in the picture below is moved upward, which way will the electrons flow?
Into the page OR Out of the page?
Out of Page
Wire moved right,
Down
List 3 factors that determine the amount of current generated when a magnet is moved is moved through closed coil of wire
Show Me The
Physics
(V) Induced voltage - also called EMF - Electromotive Force
B - Magnetic Field Strength l - length of conductor (in meters) v - velocity of conductor moving through the field
Ex) Describe the direction in which the wire could be moved to produce the maximum potential difference across its ends, R and S.
To the left or right (perpendicular to field)
Lenz's Law
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Lenz�s Law - The magnetic field around induced current opposes the wire motion that produced it. Another way to demonstrate Lenz's Law
Use a magnetic marble (Amazon)
SMUPhysics
All the left hand rules only work when moving charges are negative.
What do you do when
Right Hand Rule!
Video
Enrichment
Physics of Credit Cards Lenz's Law
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NYSSLS Reading Passage · Electricity & Magnetism
The Light and the Lightning: The Mind of Nikola Tesla
Open Reading Passage → Regents Practice Version →Check Your Understanding
5 quick questions — pick an answer to see if you’re right.
1. Electromagnetic induction (discovered by Faraday in 1831) means current can be induced when:
2. A wire moves through a magnetic field. In which direction should it move to induce the MAXIMUM voltage?
3. A 0.50 m wire moves at 4.0 m/s perpendicular to a 0.20 T field. What is the induced voltage?
4. A magnet rests inside a coil of wire without moving. How much current is induced?
5. Lenz's Law states that the magnetic field of an induced current:
Testing a Generator Model
Students push a bar magnet into and out of a coil of wire connected to a sensitive meter. They record the maximum current for different conditions.
Table 1: Induction Trials
| Trial | Magnet Motion | Turns in Coil | Max. Current (mA) |
|---|---|---|---|
| 1 | Slow, into coil | 50 | 2 |
| 2 | Fast, into coil | 50 | 6 |
| 3 | Fast, into coil | 100 | 12 |
| 4 | Held still inside coil | 100 | 0 |
| 5 | Fast, out of coil | 100 | −12 |
Which conclusion is best supported by the data?
▶ Want a challenge? Open 6 more Regents-style questions (harder · mixed formats)
Challenge score: 0 / 6
C1. Assume the induced current is proportional to the number of turns, as shown by Trials 2 and 3, and that reversing the motion reverses the current, as in Trial 5. Predict the maximum current (including its sign) when the magnet is pulled slowly out of a 100-turn coil.
C2. Which energy transformation occurs when the students push the magnet into the coil?
C3. Place a check mark in two boxes to indicate the changes that the data in Table 1 show would increase the size of the induced current.
C4. A student makes the following claim.
Place a check mark in either the Support or Refute box. Justify your response using evidence from Table 1.
C5. Why does it feel harder to push the magnet into the coil when the coil is connected to a complete circuit?
C6. A company is designing a hand-crank emergency flashlight that uses a magnet spinning inside a coil. The engineers plan to use a coil with many more turns. Using evidence from Table 1, identify one benefit and one drawback of this design.