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Why Make Electrons Flow Anyway? 4.2.3A Ohm’s Law & Circuit Basics Ohm’s Law • Voltage results in current flow • More voltage = more current • Resistance opposes current flow • More resistance = less current V I R Example #1 • A potential difference of 25.0 volts is supplied to a circuit with 100 ohms of resistance. – How much current flows through this circuit? I=V/R I = 25.0 V / 100 Ω I = 0.25 A Example #2 • A current of 2.0 amperes flows through a 10 ohm resistance. – What voltage must be applied to this resistance? I=V/R V = IR V = (2.0 A)(10 Ω) V = 20 V Example #3 • A 10 volt battery establishes a current of 5.0 amperes in a circuit. – What is the resistance of this circuit? I=V/R R=V/I R = (10 A) / (5.0 A) R = 2.0 Ω What is a circuit? • A continuous loop through which current flows from an area of high voltage to a an area of low voltage. Circuit Elements – Voltage Sources cell battery Circuit Elements – Resistances fixed resistor variable resistor lamp Circuit Elements – Switch switch Circuit Elements – Measuring Devices voltmeter ammeter Measures: VOLTAGE Resistance: HIGH Connect to circuit: OUTSIDE Measures CURRENT Resistance: LOW Connect to circuit: INSIDE Proper Use of Meters 5V 2.5 Ω 0V 2A 2A 5V 5V NEXT 0V End of 4.2.3A