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Worksheet 8.1: Sample V=IR and P=VI Problems Ohm’s Law Voltage V Mr. Grodek Scientific Methodology 2015-16 Power = Current x Resistance = x R x ohms (Ω) I volts (V) = amps (A) Power P = Voltage x Current = V x I watts (W) = volts (V) x amps (A) Use Algebra (equation solving) to solve the following problems. SHOW YOUR WORK! 1) If 3 A of current flows through a 50 Ω resistor, what is the voltage across the resistor? 2) If 120 V is applied to a light bulb with a resistance of 240 Ω, what is the current through the bulb? 3) A heater is plugged into a 240-V outlet and draws 6 A of current. What is the resistance of the heater coil? 4) A 1200-watt hair dryer is plugged into a 120-V outlet. How much current does it draw? 5) How much power does a video game adapter/charger use if its labeled DC output is 12 V and 2.5 A? 6) A device consumes 960 W of power while drawing 4 A of current. At what voltage is its source of power? ANSWER KEY 1) V = I x R = 3 A x 50 Ω = 150 V 2) I = V ÷ R = 120 V ÷ 240 Ω = 0.5 A 3) R = V ÷ I = 240 V ÷ 6 A = 40 Ω 4) I = P ÷ V = 1200 W ÷ 120 V = 10 A 5) P = V x I = 12 V x 2.5 A = 30 W 6) V = P ÷ I = 960 W ÷ 4 A = 240 V