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Ohm's Law (R. Bolton - 2012) Ohm’s Law Example Solutions Physics, 7th Edition, Cutnell & Johnson Chapter 20.2 Pages 605-607 (R. Bolton - 2012) Ohm's Law 1 Important Formulae V AB = IR P= I= W = V AB I Δt (R. Bolton - 2012) Physics 155.3: Introduction to Electricity and Magnetism V AB R R= V AB I P = IRI = I 2 R Ohm's Law P = VAB VAB VAB = R R 2 2 1 Ohm's Law (R. Bolton - 2012) Example 1 Phototube Circuit (R. Bolton - 2012) Ohm's Law 3 Example 1 Solution: What can we say about this circuit?? I is clockwise VAG = 10V VR1 = 6V VR2 = 4V R1 = (3/2)R2 (R. Bolton - 2012) Physics 155.3: Introduction to Electricity and Magnetism Ohm's Law 4 2 Ohm's Law (R. Bolton - 2012) Example 2 A Simple (but important) Circuit Consider the following circuit. circuit What is the voltage across the resistor (VAB)? What current through the resistor? What is VA? VB? (R. Bolton - 2012) Example 2 Solution: (R. Bolton - 2012) Physics 155.3: Introduction to Electricity and Magnetism Ohm's Law 5 (12V,1.2A,???) Ohm's Law 6 3 Ohm's Law (R. Bolton - 2012) Example 3 Ammeter Circuit Consider the following circuit containing an ammeter (used to measure current) What is E?? What is the resistance of the ammeter?? (R. Bolton - 2012) Ohm's Law Example 3 Solution: 7 (12V) The resistance of the ammeter is assumed to be 0Ω . But is it really?? (R. Bolton - 2012) Physics 155.3: Introduction to Electricity and Magnetism Ohm's Law 8 4 Ohm's Law (R. Bolton - 2012) Example 4 Ammeter and Voltmeter Circuit Consider the following circuit containing a voltmeter (used to measure voltage) The voltmeter reads 9 9.00 00 volts and the ammeter reads 300mA. What is the resistance of the resistor R?? What is the resistance of the voltmeter?? (R. Bolton - 2012) Ohm's Law Example 4 Solution: 9 (30Ω) The resistance of the voltmeter is assumed to be ∞Ω. But is it really?? (R. Bolton - 2012) Physics 155.3: Introduction to Electricity and Magnetism Ohm's Law 10 5 Ohm's Law (R. Bolton - 2012) Example 5 Electrical Energy Conversion Consider the following circuit At what rate is electrical energy converted to heat by the resistor in the circuit? (R. Bolton - 2012) Ohm's Law Example 5 Solution: (R. Bolton - 2012) Physics 155.3: Introduction to Electricity and Magnetism 11 (2.25W) Ohm's Law 12 6 Ohm's Law (R. Bolton - 2012) Example 6 Chemical Energy Consider the following circuit with E=120 V and R=144Ω. At what rate does the resistor convert electrical energy to heat? At what rate does the battery convert chemical energy to electrical energy? (R. Bolton - 2012) Ohm's Law Example 6 Solution: (R. Bolton - 2012) Physics 155.3: Introduction to Electricity and Magnetism 13 (100W) Ohm's Law 14 7