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1. Describe an experiment that shows that a changing magnetic field can induce an e.m.f. in a circuit

A generator contains coils of wire that spin in a magnetic field. A potential difference (p.d.) is created or induced in the wire when it cuts across the magnetic field lines. We refer to this source of pd as induced electromotive force* (e.m.f.) or an induced voltage. Emf is measured in volts (V).

*when charge flows through a cell it is given energy by the cell.  The number of joules of energy given to each coulomb of charge that passes through the cell is the e.m.f. of the cell

Experiment:
Wrap a wire around a metal. Then connect the wire to a voltmeter or galvanometer (devices used to measure voltage/pd). If you move the metal up and down between the opposite poles of two magnets, you can see the voltage changing, indicating that e.m.f. has been induced in the wire, or that an electrical current has been produced.

The production of an e.m.f. by moving a wire in a magnetic field is known as electromagnetic induction.

1. State the factors affecting the magnitude of an induced e.m.f
• The rate/speed in which the wire moves: the faster the movement, the higher the e.m.f.
• The strength of the magnet: the stronger the magnets, the more the e.m.f. produced
• The number of coils the wire makes: when the wire is coiled around several times, the no. of magnetic fields intersecting increases, and the current/voltage produced also increases.

Notes submitted by Lintha