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Motors Coil in a Magnetic Field How does an electric motor work? DC Electric Motor Simulation Specification Aims By the end of this lesson you should be able to… • Understand that a wire at right angles to a magnetic field experiences a force. • Explain how to use Fleming’s Left Hand Rule to predict the direction of the force experienced. • Explain how a DC electric motor is maintained . axle brushes battery coil commutator magnets • Describe the effect of changing: – the size of the current – the number of turns – the strength of the magnet Motors Generators How does a Generator Work? How does a Generator Work? Increasing the size of the induced current How can the increase Specification Aims By the end of this lesson you should be able to… • Describe how an a.c. generator works, including size of an induced current be increased? the function of the the speed at which the coil rotatesslip rings. increase the strength of the magnetic field• increase the number of turns in the coil increase the total area of the coil. In a power station generator, an electromagnet is often used as this can provide a stronger Explain how a Cathode Ray Oscilloscope (CRO) works and how it can be used to construct voltage time graphs. • Explain the difference between alternating current (AC) and direct current (DC). Factors affecting induced current What is alternating current (a.c.)? Alternating current (a.c.) is an electric current that is constantly changing direction. Alternating current is produced by most generators and is used in mains electricity. Motors often work using alternating current. The voltage of alternating current is easily changed with a transformer. Alternating current can be transferred efficiently over large distances. Specification Aims By the end of this lesson you should be able to… • Describe how an a.c. generator works, including the function of the slip rings. • Explain how a Cathode Ray Oscilloscope (CRO) works and how it can be used to construct voltage time graphs. • Explain the difference between alternating current (AC) and direct current (DC). A.C or D.C. The difference between alternating voltage voltage current (a.c.) and direct current (d.c.) can be seen using an oscilloscope. For each current, the oscilloscope trace is d.c. a graph showing how the voltage of an time with time. electricity supply varies peak forward voltage peak reverse voltage a.c. time Specification Aims By the end of this lesson you should be able to… • Describe how an a.c. generator works, including the function of the slip rings. • Explain how a Cathode Ray Oscilloscope (CRO) works and how it can be used to construct voltage time graphs. • Explain the difference between alternating current (AC) and direct current (DC). voltage A.C or D.C. Specification Aims By the end of this lesson you should be able to… d.c. time The voltage of a d.c. supply is steady and always in the same direction. voltage The voltage of an a.c. supply follows a repeated pattern: it rises to a peak, returns to zero changes direction and so on. peak forward a.c. voltage peak reverse voltage time • Describe how an a.c. generator works, including the function of the slip rings. • Explain how a Cathode Ray Oscilloscope (CRO) works and how it can be used to construct voltage time graphs. • Explain the difference between alternating current (AC) and direct current (DC). Frequency of A.C. voltage The frequency of a.c. electricity is the number of complete cycles per second, which1iscomplete measuredcycle in hertz (Hz). peak forward voltage a.c. time peak reverse voltage The a.c. frequency can be determined from an oscilloscope by counting the number of complete waves per unit time. If the frequency is increased, the number of complete waves shown on the screen increases. For example, if the frequency is Specification Aims By the end of this lesson you should be able to… • Describe how an a.c. generator works, including the function of the slip rings. • Explain how a Cathode Ray Oscilloscope (CRO) works and how it can be used to construct voltage time graphs. • Explain the difference between alternating current (AC) and direct current (DC). Generators The coil is rotated manually, by a steam/water/wind powered turbine As the coil spins, flux linkage changes and so an emf is induced. AC Generators Consider one rotation of the coil Flux Linkage 0 180 360 Flux Linkage 0 AC Generators 180 360 180 360 Induced emf 0 AC Generators The gradient of the flux linkage graph represents the induced emf. Maximum gradient = maximum emf ε = ε0 sin 2 π f t epsilon 0 = peak emf