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37.1 – Electromagnetic induction

37.1 – Electromagnetic induction. Faraday & Henry both puzzled over the connection between magnetism & electricity If current produces magnetism, can mag. produce current? (Because voltage is created) Yes, as long as there is relative motion Conductor or magnet can move

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37.1 – Electromagnetic induction

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  1. 37.1 – Electromagnetic induction • Faraday & Henry both puzzled over the connection between magnetism & electricity • If current produces magnetism, can mag. produce current? (Because voltage is created) • Yes, as long as there is relative motion • Conductor or magnet can move • Before this, a voltaic cell (battery) was needed

  2. Cont. • We can increase voltage, therefore current, by: • Increasing relative speed • Increasing the # of loops magnet passes through

  3. Cont. • Current does not want to flow • Work must be done • Loop creates its own magnetic field that resists the motion of the magnet • Work done = energy supplied • Producing voltage (therefore, current) by a changing magnetic field = electromagnetic induction

  4. 37.2 – Faraday’s law • States voltage is proportional to: • Number of loops • Area of each loop • How quickly B-field changes • This voltage is what causes current • Application of Ohm’s law • The resistance & voltage determine current • Rubber < copper because of resistance

  5. 37.3 – generators & alternating current • Mechanically turning a loop inside a magnet creates a generator • Mechanical  Electrical Energy • Naturally creates alternating current

  6. Cont. • The changing number of field lines within the loop induces the voltage • Current is maximum (in one way) when loop perpend. to field & zero when parallel • The current switches directions to max. then zero • Producing alternating current (AC)

  7. 37.5 - transformers • As a switch is closed in a loop of wire (primary), current goes from zero to maximum • Therefore the B-field because of current also goes 0  max. • This changing B-field induces voltage in another loop (secondary) • Iron w/i loops intensifies fields • Changing field is produced by AC

  8. Cont. • These primary & secondary loops are used to change voltage  transformer • The voltage can be stepped-up or stepped down depending on relative turns (loops) or wire • Step up = more turns in secondary • A linear relationship

  9. Cont. • Conservation of energy still is valid • Energy in = energy out, energy per time = power • The times are the same  power in = power out • Pin = Pout  (IV)in = (IV)out • There is a tradeoff between voltage & current • Easy to change voltage, main reason we use AC (not DC)

  10. 37.6 – power transmission • Power is transmitted at high voltage because we need low current • High current = high heat = huge energy loss • A series of step down transformers changes voltage to household voltage

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