Electromagnetic Induction!

Starter – Describe and explain Describe the movement of the wire. Explain why the wire moves Explain the purpose of the commutator?

Current and magnetic field We know that a current produces a magnetic field and we know that the current will be affected by placing a magnet nearby N S

Which way is the force acting? 1. S

Which way is the force acting? 2. S

Which way is the force acting? 3. S N

DC Motor We know that we can generate kinetic energy (movement) by supplying an electric current. Is the opposite true? Can we generate an electric current by moving something?

Yes!! We know this thanks to Michael Faraday the discoverer of electro-magnetic induction, electro-magnetic rotations, field theory and much else besides a very devout man (Sandemanian sect) took electricity from being a scientific curiosity to a practical technology a brilliant spellbinding orator

What is electromagnetic induction? the production of an electric current by the movement of a conductor in a magnetic field or by the movement or change in the magnetic field around a conductor the inverse of the motor effect

How and when does EM induction take place? When a conductor cuts across the field lines of a magnetic field a current is induced in the conductor The direction of the current is always such that it opposes the motion which caused it.(Lenz’s law)

EM Induction If a magnetic is moved towards or away from a coil, an EMF is induced (created). What is an EMF? What do you notice about the current? Galvanometer- measures small current

EM Induction An electric current is induced because the magnetic field around the coil is changing (the coil ‘cuts through’ the lines of field).

EM Induction How could we increase this current? Move the wire faster What would happen if this loop of wire moved up and down through a magnetic field? How could we increase this current? Move the wire faster Use a stronger magnet Increase the length of wire in the magnetic field

Electromagnetic Induction This can be investigated using the following pieces of equipment: If a stronger magnet is used, the size of the induced voltage increases, resulting in a larger current. A galvanometer is an instrument for measuring, or detecting, very small currents. If the number of turns in the coil is increases, the size of the induced voltage increases, resulting in a larger current. If the magnet moves faster, the size of the induced voltage increases, resulting in a larger current. As the magnet moves in an out of the coil, a current is induced that periodically changes direction. This is called an alternating current. When a magnet moves into a coil of wire, a voltage is induced and current flows in one direction. The size of the induced voltage can be increased by: When the magnet moves out of the coil, the polarity of the induced voltage reverses and the current flows in the opposite direction. When the magnet stops moving there is no induced voltage and no current flows When a magnetic field ‘cuts’ though a conductor, a voltage is induced, resulting in a flow of electric current. This is called electromagnetic induction. increasing the strength of the magnet increasing the number of turns in a coil increasing the speed of the magnet coil of insulated wire permanent magnet -1 +1 -2 +2 galvanometer

Faraday’s law of electromagnetic induction The EMF induced in a conductor is proportional to the rate at which magnetic field lines are cut by the conductor.

Quick Quiz What are two ways to induce a current? How can you increase the current induced? What type of current is produced when moving a magnetic in and out of a loop of wire? Name two ways you can reverse the direction of the induced EMF and current Move a wire through a magnetic field or move the magnetic field Move the wire/field faster, stronger field, increase the length of wire Alternating current (A/C) Move the wire/magnet in the opposite direction, reverse the magnetic field (turn the magnet round)

Lenz’s Law An induced current always flows in a direction such that it opposes the change which produced it. Without the use of an ammeter, how can we predict the direction of an induced current?

Fleming’s Right Hand Rule!

Left Hand or Right Hand?? To find out the force from the current its Left hand To find out the current from the motion its Right hand Motion Magnetic field Induced Current

What direction does the current travel? Motion Motion Magnetic field Induced Current

Try yourself 1. N Motion Motion Magnetic field S Induced Current

Try yourself 2. N Motion Motion Magnetic field S Induced Current

Try yourself 3. S N Motion Motion Magnetic field Induced Current

Eddy Currents Eddy currents can be used to slow down a magnet with a non-magnetic metal A metal that is non-magnetic but conducts a current will generate Eddy Currents when it moves near a magnet. These currents oppose the motion of the metal and cause it to slow down.

Watch the video and answer these questions What type of current is used to levitate the plate? What type of metal is the plate made from? Is it magnetic? Do the two magnetic fields on faraday’s ring attract or repel each other? How large is the current being passed through the wires? What type of currents do you think are being generated in the metal plate (think of the material the plate is made from) What type of energy is a by-product these currents? Alternating Current (A/C) Aluminium, No Repel 800 A Eddy Video Heat

Generating Current By moving a magnet in and out of a coil of wire an alternating current (a.c.) is being generated Video

Alternating Current

Generator/Dynamo A generator works by rotating a coil in a magnetic field (or rotating a magnet in a coil). A commutator produces alternating current (a.c.)

AC Generator Most of our electricity comes from electric generators. Simply put it is a coil of wire spun inside a magnet and an A.C current is produced

DC Generator The easiest way to make an A.C. generator D.C. is to add a commutator. How does a commutator work?

True or False Write down the true statements and write corrected versions of the false statments where possible