Electromagnetic Induction Starter Describe and explain 1 Describe
Electromagnetic Induction!
Starter – Describe and explain 1. Describe the movement of the wire. 2. Explain why the wire moves 3. 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. N S
Which way is the force acting? 2. N 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 • Michael Faraday 1791 -1867 § 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 • What would happen if this loop of wire moved up and down through a magnetic field? How could we increase this current? 1. Move the wire faster 2. Use a stronger magnet 3. Increase the length of wire in the magnetic field
Electromagnetic Induction Asathe This A If The When galvanometer the stronger size can number magnet the aamagnet be of magnet the investigated magnet moves of induced moves is moves turns an moves stops faster, isinstrument in voltage used, in using into moving an the out athe coil the of can coil size for size of there following isbe measuring, of the increases, of coil, of increased wire, the is coil, the no pieces induced aainduced polarity voltage current the orby: of detecting, size voltage equipment: voltage is of ofainduced the increases, very induced and small and that no magnetic field ‘cuts’ though athe conductor, voltage is voltage currents. resulting current periodically flows reverses increases, inresulting a changes in larger one and resulting current. direction. in a larger This flows iscurrent. incalled the current. opposite an alternating direction. induced, inthe acurrent flow of electric This current. is called ● increasing the strength of the electromagnetic induction. ● increasing the number of turns in magnet ● the speed of the a increasing coil of insulated magnet wire permanent magnet 0 +1 + -2 -1 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 a wire through a magnetic 1. What are two ways to induce a current? Move field or move the magnetic field Move the wire/field faster, 2. How can you increase the current induced? stronger field, increase the length of wire 3. What type of current is produced when moving a magnetic in and out of a loop of wire? Alternating current (A/C) 4. Name two ways you can reverse the direction of Move the wire/magnet in the opposite direction, reverse the induced EMF and current 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 current from the motion its Right hand Ma gn etic t Ind ed c u C en r r u Motion To find out the force from the current its Left hand fiel d
What direction does the current travel? S Ma gn eti du n I d ce C en r ur cf Motion N t ield
1. Try yourself Ma gn eti S du n I d ce C en r ur cf Motion N t ield
2. Try yourself Ma gn eti S du n I d ce C en r ur cf Motion N t ield
S Try yourself N Ma gn eti du n I d ce C en r ur cf Motion 3. t ield
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 1. What type of current is used to levitate the plate? Alternating Current (A/C) 2. What type of metal is the plate made from? Is it magnetic? Aluminium, No 3. Do the two magnetic fields on faraday’s ring attract or repel each other? Repel 4. How large is the current being passed through the wires? 800 A 5. What type of currents do you think are being generated in the metal plate (think of the material the plate is made from) Eddy 6. What type of energy is a by-product these currents? Heat Video
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
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