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The Measurement of Current and Voltage

The Measurement of Current and Voltage. 20.11. Non-digital. Main component  galvanometer. Ammeters. Measures current Inserted into circuit so current passes through it Connected in series. Ammeter. Coil usually measures only little current

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The Measurement of Current and Voltage

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  1. The Measurement of Current and Voltage 20.11

  2. Non-digital • Main component  galvanometer

  3. Ammeters • Measures current • Inserted into circuit so current passes through it • Connected in series

  4. Ammeter • Coil usually measures only little current • Has shunt resistors connected in parallel to galvanometer so excess current can bypass • A knob lets you select which shunt resistor is used

  5. Problems with Ammeters • The resistance of the coil and shunt resistors add to the resistance of the circuit • This reduces the current in the circuit • Ideal ammeter has no resistance • Real-life good ammeters have small resistance so as only cause a negligible change in current

  6. Voltmeter • Connected in parallel to circuit • The coil works just like in the ammeter • Given the current and the resistance of the coil  V = IR • To give more range, a large resistor is connected in series with the coil

  7. Problems with Voltmeters • The voltmeter takes some the voltage out of the circuit • Ideal voltmeter would have infinitely large resistance as to draw tiny current • Good voltmeter has large enough resistance as to make the current draw (and voltage drop) negligible

  8. Practice Problems • See if you measure up to these meter problems • 612 CQ 14, 15 P 80, 81, 83 • Total of 5 Problems

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