Charged Particles In Circular Orbits Learning Objectives Book Reference : Pages 120-122 To understand how to generate electricity using electromagnetic induction To be able to establish the relative direction of the field, motion & induced current by using the “dynamo rule”

Generating Electricity 1 With the exception of photovoltaic cells, every other means of practical electricity generation relies on an alternator or dynamo to convert rotational kinetic energy in to electricity. The kinetic energy is either available directly : Wind power, hydroelectric, wave power & tidal power Or a fuel is used to produce heat which in turn produces steam which spins a steam turbine to provide the kinetic energy. Xturbgen1.swf Xph_energy05.swf

Electromagnetic induction We have seen that a conductor experiences a force when it carries current perpendicular to a magnetic field. This is the basis for the electric motor. What will happen if the same set up is utilised but with no supplied current & with an external force providing perpendicular motion to the wire? Supplied Motion N S 2_animagalvo1.swf generator_en.jar Which factors effect the magnitude & direction of the electricity produced?

Important Factors The strength of the magnetic field How fast the wire is moved (no movement, no current) The area of wire in the field (i.e. Make a coil) The direction the wire is moved (Should be perpendicular to field). The wire must “cut” the field lines Note motion only needs to be relative, we can move either the coil or the permanent magnet This process is called Electromagnetic Induction and an induced emf (electromotive force) causes the electrons to flow around the circuit

Example Dynamos 1

Example Dynamos 2

Energy Changes 1 Once again we have a conductor carrying a current perpendicular to a magnetic field. What will the conductor experience?

Energy Changes 2 Supplied Motion N S Motor force on conductor The current carrying conductor experiences a “motor force” which opposes the supplied motion. “Work” must be done to keep the dynamo spinning. (Assuming no losses) the work done spinning the dynamo will equal the energy transferred to the circuit (e.g. To light a lamp)

Energy Changes 3 The rate at which energy is transferred from the source of motion is equal to the electrical power supplied to the components in the circuit : Electrical power = induced EMF x Current (voltage) Induced EMF is the energy supplied to each unit charge & current is the charge flow per second Electrical Power = Energy transferred per s from source

Understanding Induction 1 We have seen that a charged particle in an electric field experiences a force Beam of electrons Magnetic Field Into page - Resultant direction Force A conductor can be thought of as a tube containing lots of free electrons. If the “tube” crosses a magnetic field, then the electrons will experience a force which moves them to one end. Thus one end of the wire becomes negative relative to the other. An electromotive force is induced in the wire

Understanding Induction 2 Conductor Relative +ve charge + + + Magnetic Field Into page Direction of Movement - Free Electron Force Relative –ve charge - - - When part of a complete circuit, the induced EMF causes a current to flow in the circuit

The Dynamo Rule We have previously used “Fleming’s left hand motor rule”. Since a dynamo is effectively an electric motor used backwards we can apply a similar rule here “Fleming's right hand dynamo rule” Remember CONVENTIONAL CURRENT Thumb (Motion) First (Field) Second (Current)