1. Charged Particles In Circular Orbits
Learning Objectives
Book Reference : Pages
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”

2. 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

3. 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?

4. 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

5. Example Dynamos 1

6. Example Dynamos 2

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

8. 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)

9. 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

10. 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

11. 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

12. 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)