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# Electromagetic effects

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### Electromagetic effects

1. 1. Lets watch a video clip…
2. 2. Is there a battery source? What is that “piece of thing” that the person is holding? Why is there a current?
3. 3. Electromagnetic Effects Phenomenon of inducing an emf in a circuit due to a changing magnetic field.
4. 4. Faraday’s experiments <ul><li>Experiment to show that a changing magnetic field can induce an emf in a circuit </li></ul>
5. 5. Faraday’s experiments <ul><li>a) Faraday’s solenoid experiment </li></ul>- Set up the apparatus as shown in the diagram. - A permanent magnet is inserted into a solenoid connected to a sensitive galvanometer. - The galvanometer needle deflects as the permanent magnet move within the solenoid. - This shows that e.m.f. can be induced when there is a changing magnetic field.
6. 6. Factors affecting the magnitude of the induced emf Greater deflection Insert N pole of 1 bar magnet into solenoid with twice the number of turns Greater deflection Insert N pole of 2 bar magnets into solenoid Greater deflection Insert N pole of 1 bar magnet into solenoid at twice the speed Slight deflection Insert N pole of 1 bar magnet into solenoid Galvanometer response Procedure
7. 7. Factors affecting the magnitude of the induced emf <ul><li>The speed with which the magnet is inserted into or withdrawn from the solenoid. </li></ul><ul><li>The strength of the magnet. </li></ul><ul><li>The number of turns in the solenoid. </li></ul>
8. 8. Determine the direction of the induced current <ul><li>Lenz’s Law </li></ul><ul><li>The direction of the induced emf and hence induced current in a closed circuit is always such as to oppose the change in magnetic flux producing it </li></ul>
9. 9. Deflection to the left Solenoid move towards N pole of magnet Deflection to the right Solenoid withdraw from the same magnet Deflection to the left Withdraw the same bar magnet out of solenoid Deflection to the right Insert S pole of 1 bar magnet into solenoid Deflection to the right Withdraw the same bar magnet out of solenoid Deflection to the left Insert N pole of 1 bar magnet into solenoid Galvanometer response Procedure
10. 10. Thinking corner 1 <ul><li>What will be the direction of the induced current if the magnet remains at rest (no movement)? </li></ul>No induced current produced. Why? There’s no change in magnetic field.
11. 11. Thinking corner 2 <ul><li>If we want to have a continuous flow of induced current, what can we do? </li></ul><ul><li>Constant change in magnet field </li></ul><ul><li>Moving the magnet in and out of the solenoid continuously </li></ul>