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- 1. Electromagnetic Induction
- 2. <ul><li>All magnets are surrounded by field lines that by definition are called lines of force and run from the North pole to the South pole. </li></ul><ul><li>Where these are close together ,the field is strong e.g. near to the poles. </li></ul><ul><li>So we also need to consider the area over which these field lines act. </li></ul>
- 3. <ul><li>Flux combines the strength of the magnetic field and the area through which the field lines pass. </li></ul><ul><li>Flux Φ = BA sin θ </li></ul>
- 4. <ul><li>There is more flux near the poles of a magnet than on the sides as there are more field lines in an area near the poles than in the same area on the side. </li></ul>
- 5. <ul><li>Example </li></ul><ul><li>How much flux if a field of 5 Tesla acts at 35 º to an area of 0.2 m² ? </li></ul><ul><li>Φ = 5 x 0.2 x sin 35 </li></ul><ul><li>= 0.574 Weber </li></ul>
- 6. <ul><li>If we move a magnet in a coil , the wires will be forced to cut field lines. </li></ul><ul><li>This generates a force on the conductors in the wire. </li></ul><ul><li>The conductors ( electrons ) will move, generating a current. </li></ul><ul><li>We use Flemings right hand rule to find the direction of the current. </li></ul>
- 7. <ul><li>If we consider a coil of N turns , then we have N loops of wire. </li></ul><ul><li>The magnetic flux linking the coil is called the flux linkage and is defined as N Φ </li></ul><ul><li>This can be written as BAN sin θ </li></ul>
- 8. Faraday’s Law <ul><li>If a conductor passes through a magnetic field , the electrons will experience a force. </li></ul><ul><li>If the conductor is not a complete circuit, an EMF will be produced across its ends. </li></ul><ul><li>This EMF will depend on the rate at which the field lines are cut. </li></ul><ul><li>E d Φ </li></ul><ul><li>dt </li></ul>
- 9. <ul><li>As the constant of proportionality is 1 , the equation becomes E = - d Φ </li></ul><ul><li>dt </li></ul><ul><li>For a coil of N turns E = - N d Φ </li></ul><ul><li>dt </li></ul><ul><li>The minus sign is because it opposes the motion that created it. </li></ul>
- 10. <ul><li>Remember </li></ul><ul><li>B is Flux Density measured in Tesla </li></ul><ul><li>Φ is flux measured in Weber </li></ul>

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