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Exp 2 Pre-lab (Ohm's Law and Electric Circuits)

# Exp 2 Pre-lab (Ohm's Law and Electric Circuits) - the...

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PHYS105. EXP2: Ohm’s Law and Electric Circuits Prelab Questions: 1. How can you tell from an I-V curve if a device is ohmic? A device is ohmic if it satisfies Ohm’s law: V = IR. An IV curve can indicate if this relationship is valid by displaying I vs. V. If the I-V characteristic is a straight line, then the piece of conductor satisfies this law. 2. Explain why an ammeter must be connected in series with a resistor An ammeter is connected in series with a resistor because ammeters have very low resistance and will not significantly affect the total circuit resistance. The current measured is affected very minimally by the ammeter being run in series. If they were hooked up in parallel, a sizeable portion of the current would run through the ammeter as well as the resistor. 3. Explain why a voltmeter must be connected in parallel with a resistor A voltmeter must be connected in parallel with a resistor because voltmeters have large resistance. Only a small portion of the circuit’s voltage will be diverted through
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Unformatted text preview: the voltmeter if it is set up in parallel, allowing the rest to flow through the actual resistor. On the other hand, if the voltmeter were added in series, the total circuit resistance would be significantly affected. 4. When used as an ohmmeter, a Fluke 77 meter gives a reading of 571.5 ohm for a resistor that has a nominal resistance of 560 ohm +/- 5%. What resistance value and uncertainty should be reported for this resistor? The resistance value of 571.5 ohm falls within the nominal resistances uncertainty of 5%. Therefore, the resistance can be reported as 560 ohm +/- 5%. 5. Is current used up in a circuit? What about voltage? Explain. According to the loop rule, the net change in electric potential must be zero around any loop. Therefore, voltage is not used up in a circuit. Using the Ohms Law (V=IR), if voltage is constant and resistance increases, current decreases or is used up....
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