Lecture_17_(Chap.20)

# Lecture_17_(Chap.20) - Exam 2 Wednesday, March 30, 8-9:30,...

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Exam 2 Wednesday, March 30, 8-9:30, PHYS 112. Chap. 18-21 mphasis on conceptual problems Emphasis on conceptual problems. Practice exam on course home page. 1

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Ammeters, Voltmeters and Ohmmeters Ammeter: measures current I Voltmeter: measures voltage difference V Ohmmeter: measures resistance R 2
Using an Ammeter Connecting ammeter: Conventional current must flow into the ‘+’ terminal and emerge from the ‘-’ terminal to result in positive reading. 0.150 3

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Ammeter Design Simple ammeter using your lab kit: Simple commercial ammeter Digital ammeters: uses semiconductor elements. ADC – analog-to-digital converter ombination of comparator and DAC) 4 (Co b o o co p o d C)
Ammeter Design: r int Ammeter is inserted in series into a circuit – measured current flows through it. R emf A Process of measuring requires r int charges to do some work: Internal resistance f 0 RI emf No ammeter: R emf I emf With ammeter: 0 int RI I r emf int r R I ternal resistance of an ammeter must be very small 5 Internal resistance of an ammeter must be very small

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Exercise: Connecting Ammeter Is it correct connection? A. Yes B. No 6
Voltmeter V B – add a series resistor to ammeter Voltmeters measure potential difference AB V I R Measure I and convert to V AB = IR onnecting Voltmeter: Connecting Voltmeter: Higher potential must be connected to 7 the ‘+’ socket and lower one to the ‘-’ socket to result in positive reading.

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Voltmeter: Internal Resistance R V AB in absence of a voltmeter 1 emf B emf R R R V AB 2 1 2 R 2 A r int V AB in presence of a voltmeter f R int || 2 A emf R R V AB int || 2 1 int 2 t r R R int 2 int || 2 r R ternal resistance of a voltmeter must be very large 8 Internal resistance of a voltmeter must be very large
Ohmmeter How would you measure R?

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## This note was uploaded on 04/23/2011 for the course PHYS 272h taught by Professor Staff during the Spring '08 term at Purdue University-West Lafayette.

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Lecture_17_(Chap.20) - Exam 2 Wednesday, March 30, 8-9:30,...

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