This document discusses electromagnetic induction and Faraday's law. It explains that magnetic fields have flux lines that run from the North to South pole of a magnet. The flux Φ is calculated as BA sinθ and represents the strength of the magnetic field times the area it passes through. Faraday's law states that an electromotive force (EMF) is induced in a conductor when it passes through a changing magnetic flux. The EMF is directly proportional to the rate of change of flux linkage over time. For a coil of N turns, the EMF induced is equal to -N * (change in flux linkage over time).

1. Electromagnetic Induction

2. 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. Where these are close together ,the field is strong e.g. near to the poles. So we also need to consider the area over which these field lines act.

3. Flux combines the strength of the magnetic field and the area through which the field lines pass. Flux Φ = BA sin θ

4. 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.

5. Example How much flux if a field of 5 Tesla acts at 35 º to an area of 0.2 m² ? Φ = 5 x 0.2 x sin 35 = 0.574 Weber

6. If we move a magnet in a coil , the wires will be forced to cut field lines. This generates a force on the conductors in the wire. The conductors ( electrons ) will move, generating a current. We use Flemings right hand rule to find the direction of the current.

7. If we consider a coil of N turns , then we have N loops of wire. The magnetic flux linking the coil is called the flux linkage and is defined as N Φ This can be written as BAN sin θ

8. Faraday’s Law If a conductor passes through a magnetic field , the electrons will experience a force. If the conductor is not a complete circuit, an EMF will be produced across its ends. This EMF will depend on the rate at which the field lines are cut. E d Φ dt

9. As the constant of proportionality is 1 , the equation becomes E = - d Φ dt For a coil of N turns E = - N d Φ dt The minus sign is because it opposes the motion that created it.

10. Remember B is Flux Density measured in Tesla Φ is flux measured in Weber