week 19: electromagnetism ii - homeschool ireland

153 19.0 Learning Intentions You will be able to explain; • Electromagnetic Induction • Faraday’s Law • Lenz’s Law • ac / dc comparison • Induction • Transformers 19.1 Revision Notes Electromagnetic Induction Electromagnetic Induction occurs when an emf is induced in a coil due to a changing magnetic flux. Michael Faraday investigated the relationship between electricity and magnetism . If you moved a magnet in or out of a coil of wire, a voltage was generated (emf) This is: Faraday’s Law of Electromagnetic Induction Faraday’s Law states that the size of the induced emf is proportional to the rate of change of flux. When you move the magnet in and out of the coil slowly there is a slight deflection. Move the magnet quickly and there will be a greater deflection. Lenz’s Law Lenz’s Law states that the direction of the induced emf is always such as to oppose the change producing it. We know that when a magnet and coil move relative to each other, an emf is induced. If the coil is a conductor the induced emf will drive a current around the coil. This current has a magnetic field associated with it.The direction of this magnetic field will always be such as to oppose the change which caused it. Week 19: Electromagnetism II

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Page 1: Week 19: Electromagnetism II - HomeSchool Ireland

153

19.0 Learning Intentions

You will be able to explain;

• Electromagnetic Induction • Faraday’s Law• Lenz’s Law• ac / dc comparison • Induction• Transformers 19.1 Revision Notes

Electromagnetic Induction

Electromagnetic Induction occurs when an emf is induced in a coil due to a changing magnetic flux.

Michael Faraday investigated the relationship between electricity and magnetism .

If you moved a magnet in or out of a coil of wire, a voltage was generated (emf ) This is:

Faraday ’s Law of Electromagnetic Induction

Faraday’s Law states that the size of the induced emf is proportional to the rate of change of flux.

When you move the magnet in and out of the coil slowly there is a slight deflection. Move the magnet quickly and there will be a greater deflection.

Lenz’s Law

Lenz’s Law states that the direction of the induced emf is always such as to oppose the change producing it.We know that when a magnet and coil move relative to each other, an emf is induced. If the coil is a conductor the induced emf will drive a current around the coil. This current has a magnetic field associated with it.The direction of this magnetic field will always be such as to oppose the change which caused it.

Week 19: Electromagnetism II

154

Magnetic Flux

Magnetic flux is the product of the average magnetic field times the perpendicular area that it penetrates.

Alternating Current

Alternating current is current which changes direction periodically.In AC electricity the voltage can be readily changed, thus making it more suitable for long-distance transmission than DC electricity.AC can employ capacitors and inductors in electronic circuitry, allowing for a wide range of applications.

Comparing AC to DC

The value of an AC voltage is continually changing from zero up to the positive peak, through zero to the negative peak and back to zero again.We take the r.m.s value because the magnitude of the r.m.s. alternating current will have the same heating effect as a direct current of the same magnitude.

e.g. If the r.m.s. value of an alternating current is 2A, it will the same heating effect as 2A direct current.

Mutual Inductance

Mutual inductance is where the magnetic field generated by a coil of wire induces voltage in an adjacent coil of wire.

Week 19: Electromagnetism II

155

Transformers

A transformer is a device constructed of two or more coils in close proximity to each other, with the express purpose of creating a condition of mutual inductance between the coils.

Week 19: Electromagnetism II