202/3 – Know the principles of electro-magnetism

Outcome 3.2 – Apply Fleming’s right hand rule to the operating principles of a

simple alternator

Outcome 3.3 - Calculate magnitudes of a generated EMF

Unit 202 Principles of electrical science

3.1 Describe the magnetic flux patterns of electromagnets

Current carrying conductor, solenoid, inductor, magnetic poles, relays.

Last session

Review Of Previous Sessions

• In a magnetic field unlike poles attract each other, like poles repel each other

• The amount of lines of flux in any particular area is called the flux density• When a conductor carries a current, a magnetic field forms around it.

• To strengthen the effects of the magnetic force around a conductor a coil is used.

• The strength of the magnetic fields around the coil depends on the number of turns on a coil the material the coil is wrapped around and the current from the supply.

• The negative effect of a magnetic field are eddy currents.

3.2 Apply Flemings right hand rule to the operating principles of a simple alternator

3.3 Calculate magnitudes of a generated EMF

This session

An alternator is a device that converts mechanical energy to electrical energy in the form of alternating current.

It used a coil of wire called?It uses a fixed magnet called?

Alternator

Alternator

A coil of wire rotating in a permanent magnetic fields will

generate an A.C. voltage.

the principles of alternator operation

the principles of alternator operation

the principles of alternator operation

This basic principle occurs in every power

station.

the principles of alternator operation

Calculate generated EMF

When an alternator is turned, a current flows.

What pushes a current round a circuit?

Calculate generated EMF

A voltage pushes a current round a circuit.

When generated, this is called an electromotive force or e.m.f.

Calculate generated EMF

In an alternator the e.m.f. generated depends on 3 things.

In groups try to list them.

Calculate generated EMF

In an alternator the e.m.f. generated depends on 3 things.

• The magnetic flux density• Length of the conductor• The velocity (speed) of the

conductor

Calculate generated EMF

Think back to SI units, what units are these values measured in?

• The magnetic flux density• Length of the conductor• The velocity (speed)of the

conductor

Calculate generated EMF

Think back to SI units, what units are these values measured in?

• The magnetic flux density teslas (B)

• Length of the conductor metre (L)

• The velocity of the conductor m/s (v)

Calculate generated EMF

As each of these factors increases, the e.m.f. induced will increase.Work out the formula?

e.m.f. =

• The magnetic flux density teslas (B)• Length of the conductor metre (L)• The velocity of the conductor m/s (v)

Calculate generated EMF

e.m.f. = B (teslas) x L (m) x v (m/s)

Transpose:-Make B the subjectMake L the subject

Individual task

Calculate generated E.M.F. Mag flux density = 10TLength of conductor = 1mVelocity of conductor = 3 m/s

Individual task 2

Calculate generated E.M.F. Mag flux density = 4 TLength of conductor = 50cm (careful)Velocity of conductor = 25 m/s

Stretch and challenge on board

consolidation

3.2 Apply Flemings right hand rule to the operating principles of a simple alternator?

3.3 Calculate magnitudes of a generated e.m.f. formula?

3.4 State how an alternator produces a sinusoidal waveform output

3.5 Calculate sinusoidal quantities

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