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Question
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Answer
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Who discovered the motor effect?
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Michael Faraday
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What is the name for the generation of an emf through the use of a magnetic field?
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Electromagnetic Induction
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What device is used to detect small electrical currents?
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Galvanometer
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In Faraday's initial experiment with two separate coils, there was a current induced into the coil with no battery. However this current was only _________.
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Temporary
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Faraday's second notable experiment on induced currents featured an ____ ____. This had a greater induced current but it was also ^.
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Iron ring
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Compared to moving a magnet into a coil, what direction does the deflection in the galvanometer read when the magnet is brought away from the coil.
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The opposite direction
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A faster moving magnet near a coil induces a ______ current.
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Larger
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Magnetic field lines move away from which pole
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The North Pole
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What is the name given to the amount of magnetic flux through a given area?
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Magnetic flux
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It's symbol is the greek character phi, but what is it's SI unit?
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Weber (Wb)
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What is magnetic field strength is also known as when it passes through a given area?
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Magnetic Flux Density
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What is magnetic field strength, B, measured in?
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Tesla (T)
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What does emf stand for?
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Electromotive force
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What is the magnitude of generated emf is determined by?
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The rate at which the magnetic flux changes
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What is emf is inversely proportional to?
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The change in time
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Lenz's Law: An induced current always _____ ___ to a current that creates a magnetic field that _______ the original change in ____ through the circuit.
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Gives rise
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Opposes
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Flux
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In other words an "induced" magnetic field ______ what causes the change in flux through a circuit.
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Repels
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What law is Lenz's Law a consequence of?
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The law of conservation of energy?
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In electric motors, an induced emf is created in the current-carrying coil because it is moving in a magnetic field. What direction compared to the current is the emf travelling?
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The opposite direction
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What is this emf also known as?
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Back emf
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If there is nothing to slow it down, the speed of the armature coil in a motor increases until the back emf is equal to what?
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The external emf
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When this happens no voltage and therefore no current passes through the coil. There is also now no net force on the coil so it rotates at a ________ ____.
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Constant rate
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When a load is added the coil rotates slower so back emf is reduced. This results in a higher current which could burn out the motor. What device is used to protect motors from an initially high current when they are switched on?
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A series resistor
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What is created every time a conductor moves through an external magnetic field or vice versa? They are an application of Lenz's Law.
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Eddy currents
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What direction do these produced magnetic fields travel compared to the external magenetic field direction. (They travel in circles/whirls)
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Perpendicular
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What is the most common example of an induction switching device?
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Metal detector
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These devices create electromagnetic fields to induce eddy currents into detectable metals. These eddy currents place a load on the coil, changing the _________ of the oscillator.
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Frequency
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By switching on an electromagnet close to a wheel, what can we use eddy currents for in cars and trains?
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Electromagnetic breaking
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Eddy currents also cause an increase in ____ which can be helpful in the kitchen.
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Heat
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The process of using this property in induction cookers and furnaces is called what?
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Induction heating
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