Plot a graph of EMF against time as

Plot a graph of EMF against time as the coil passes through the field Click either Move Fast or slow Box to activate animation x x x X x x V Move Slow Move Fast V V bigger Flux constant because flux changes quicker Flux increases as coil enters field Flux decreases as coil leaves field t

V x x X x The coil moves at 1 ms-1 and has size 1 m by 2 m. If B = 0. 1 T and coil has 10 turns then calculate V. 2 1 E = - NΔ /ΔT 2 4 -2 5 = - 10 x BA/1 = -10 x 0. 1 x 2 /1 = -2 V

Generators

Generators Describe how a rotating-coil generator works: • The coil is mounted in a strong magnetic field • When the coil is mechanically rotated (eg high pressure steam in a coal fired power station) by Faraday’s Law, a current is induced in the wire. • Due to Lenz’s Law the current direction alternates in order to appose the rotation motion. Graph of voltage output against time for an A. C. Generator • The induced Voltage is a sine curve, has min & max (when wire is about to ‘cut’ lots of field lines), as well as +ve & -ve values Key concept: Mechanical Energy convert to Electrical Energy

Here a ‘large’ number of Magnetic field lines are being ‘cut’ by the coil Here the coil is moving parallel to the Magnetic field lines and none are being ‘cut’

This like an electric motor in reverse. As the coil is rotated electromagnetic induction occurs. An alternating voltage is induced in the coil. An alternating current is drawn off through two slip rings. The faster the coil is rotated: - the greater is the amplitude of the voltage and current - the higher is the frequency of the a. c.

Question 1 The graph opposite shows how the voltage of a generator varies in time. Using the same set of axes show the voltage would vary if the rotational speed of the generator was doubled. V time The new voltage will have TWICE the amplitude AND frequency of the original.

Question 2 Choose appropriate words to fill in the gaps below: The _____ generator effect occurs when a conductor is moved magnetic relative to a ______ field. This is also known as induction electromagnetic ______. movement of the conductor and The greater the relative _____ greater is the voltage ____. induced magnetic field the _______ complete circuit an electric If the conductor is part of a ____ current will flow. alternating ______ current is produced if the direction of movement reversed is continually _____. WORD SELECTION: generator magnetic complete alternating induction induced greater reversed movement