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Understanding Electromagnetic Induction in Magnetism and Current

Explore the fascinating connection between magnetism and electricity through electromagnetic induction, Faraday's law, generators, transformers, and power transmission. Learn how changing magnetic fields induce voltage and current, the principles behind transformers, and why high-voltage transmission is preferred for efficiency.

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Understanding Electromagnetic Induction in Magnetism and Current

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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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