ELECTRODYNAMICS - GR10 by Lizelle Swanepoel

MOTORS AND GENERATORS

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ELECTRODYNAMICS = A branch of mechanics studying the interaction of electric currents with magnetic fields.

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WHAT WE WILL BE STUDYING IN THIS SECTION

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1. MOTORS
Energy conversion: Electrical energy 🡆 Kinetic energy

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2. GENERATORS
Energy conversion: Kinetic energy 🡆 Electrical energy

WHAT PHENOMENON IS ILLUSTRATED BELOW?

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Click to watch the video:

THE MAGNETIC EFFECT OF CURRENT

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Discovered by Hans Christiaan Oersted
This effect is called the electromagnetic effect

OUR STORY STARTS WITH HANS CHRISTIAAN OERSTED (DANISH PROFESSOR)

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Hans Christiaan Oersted was a Danish Professor who discovered the link between electricity and magnetism. Watch the short video above:

MAGNETISM

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MAGNETIC FIELD = The region around a magnet where another magnetic material will experience a force.

Magnetic field direction is N to S outside the magnet.
Magnetic field direction is S to N inside the magnet.
Magnetic field lines representing the strength and direction of the magnetic field.
Magnetic field lines are continuous lines, forming closed loops.

ONLY THREE METALS ON EARTH ARE NATURALLY MAGNETIC:

Fe, Co, Ni. (they are called ferromagnetic)

MAGNETIC FIELDS CAN BE PRODUCED BY ELECTRIC CURRENTS

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Magnetic fields are produced by electric currents, which can be currents in wires (or microscopic currents associated with electrons in atomic orbits).

EFFECTS OF AN ELECTRIC CURRENT (I.E. MOVING CHARGE):

Heating
Magnetism

In electrodynamics we study the magnetic effect resulting from current flowing in a wire.

When charge moves in a medium, it generates a magnetic field perpendicularly around that medium.
This is electromagnetism (Below is an electromagnet).

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MAXWELL'S RIGHT HAND GRIP RULE

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The right hand rule is used to find the direction of the magnetic field lines around a current carrying conductor (CCC).

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RIGHT HAND SOLENOID RULE

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Curly fingers = points in direction of current in solenoid.
Thumb = points to NORTH POLE generated by current in the solenoid.

OR

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THE MOTOR EFFECT

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FLEMING'S LEFT HAND RULE - USED FOR MOTORS

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HAND RULES EXPLAINING INTERACTION BETWEEN CURRENTS AND MAGNETIC FIELDS

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Right Hand Grip Rule
Fleming Left Hand Rule

A CURRENT-CARRYING CONDUCTOR PLACED IN 2ND MAGNET FIELD

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Both magnetic fields interact.
The magnetic field between the opposite poles and the magnetic field around the current-carrying conductor reinforce each other on one side of conductor
and cancel each other on the other side.
A Lorentz force is created = the force acting on the ccc in a MF

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MOTOR EFFECT HOMEWORK

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MOTOR EFFECT HOMEWORK: ANSWERS

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THE DC MOTOR

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THE SPLIT RING COMMUTATOR FUNCTION

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VIDEO ANIMATION - HOW A MOTOR WORKS

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ANSWERS: EX 2-3

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GENERATORS

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GENERATORS EXPLAINED BY ELECTROMAGNETIC INDUCTION

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MOTOR VS. GENERATOR COMPARISON

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ELECTROMAGNETIC INDUCTION ILLUSTRATED

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THE PARTS OF THE AC GENERATOR

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ALTERNATOR

AC GENERATOR

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FLEMING'S RIGHT HAND RULE - USED FOR GENERATORS

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Use this hand rule to determine the direction of flow of CURRENT induced within the coil.

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THE LORENTZ FORCE

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A generator is a device that converts E_k --> E_electric. It is a motor in reverse.

In a motor:

A current is passed through a coil in a magnetic field, causing a force and the coil MOVES. A motor works on the principle of the motor effect.

In a generator:

A coil is rotated through a magnetic field, CAUSING A CURRENT to flow in the coil as the wire cuts across the magnetic field. This causes a changing magnetic field.
A generator works on the principle of electromagnetic induction.
Induction = the production of current in a conductor as it moves through a changing magnetic field.
Faraday's Law of Induction applies in generators, stating that:
if a wire is moved back and forth in a magnetic field, it cuts across the lines of magnetic flux. This magnetic field pushes on electrons in the metal. This movement of electrons is electrical flow.

The strength of a generator or motor depends on:

"B" - Strength of the magnetic field (flux density of the magnet)
"I" - Current flowing or generated in the coil
"ℓ" - Length of the conductor in the magnetic field
"θ" - Angle between the conductor and the fixed magnetic field
Use this formula for calculations:
- F = B x I x ℓ x sin θ (Coil is always 90 degrees to MF)
- Also: F = Bqv ; q=charge, v=speed of rotor

THE AC GENERATOR (ALTERNATOR)

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AC vs. DC GENERATOR

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AC Generator = An ALTERNATOR
DC Generator = A DYNAMO

An MG Spitfire

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Use this to remember:

Motors = Left Hand Rule
Generators = Right Hand Rule

FACTORS AFFECTING EMF OF A GENERATOR

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Factors affecting induced emf:

Position of the coil
- If parallel to the external magnetic field (B), then flux lines are not 'cut' and zero induced emf is generated.
- If perpendicular to an external magnetic field (B), then flux lines are being 'cut' and an induced emf is generated.
Strength of the magnetic field
Number of turns on the coil
Area of the coil
Coil wound around an iron core or not.
Rotation speed of the coil
- i.e. Rate of change in magnetic flux or rate with which coil "cuts" across the permanent magnetic field

USES OF AC GENERATORS

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Power plants have generators rotated by water or steam.
Car alternators charge battery when driving.
Diesel/petrol generators as alternative power supply when off-grid.
Moving coil microphones use alternators.
- Sound waves vibrate a membrane which move a coil in a magnetic field.
- This induces a varying current which gets amplified and fed to a loudspeaker.

EXAM STYLE QUESTION

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ANSWERS

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TRANSFORMERS: P=IV, Np/Ns = Vp/Vs = Is/Ip

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PURPOSE OF A TRANSFORMER = It is used to increase or decrease AC voltage.

The Number of turns on the primary and secondary coils affect the input and output voltages.

What type of transformer is this?

TRANSFORMERS EXPLAINED

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TRANSFORMER EQUATIONS YOU NEED TO KNOW

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WATCH THIS VIDEO EXPLAINING TRANSFORMERS

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ANSWERS (Ex4 -10; p26-61)

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MOTORS - EXAM QUESTION

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GENERATORS - EXAM QUESTIONS

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Transformers Question

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GR 10 BISHOPS NOTES - ELECTRODYNAMICS

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DC GENERATOR - CAN YOU NAME THE PARTS?

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TRANSFORMERS WORK ONLY WITH AC - NOT DC CURRENT

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TRANSFORMER

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Faraday's law of electromagnetic induction = The electromotive force (EMF) induced in a circuit is directly proportional to the rate of change of magnetic flux through the circuit.

lizellexs — 2025-09-16 07:01:44 UTC