1. Base your answers to the question on the information below. A copper wire at 20°C has a length of 10.0 meters and a cross-sectional area of 1.00 × 10-3 meter2. The wire is stretched, becomes longer and thinner, and returns to 20°C. What effect does this stretching have on the wire’s resistance? 1.Resistance stays the same 2.Resistance decreases 3.Resistance is halved 4.Resistance increases What effect does this stretching have on the wire’s resistivity?

2. 4.2.3A Ohm’s Law & Circuit Basics Why Make Electrons Flow Anyway?

3. Ohm’s Law Voltage results in current flow More voltage = more current Resistance opposes current flow More resistance = less current

4. A potential difference of 25.0 volts is supplied to a circuit with 100 ohms of resistance. –How much current flows through this circuit? Example #1 I = V / R I = 25.0 V / 100 Ω I = 0.25 A

5. A current of 2.0 amperes flows through a 10 ohm resistance. –What voltage must be applied to this resistance? Example #2 I = V / R V = IR V = (2.0 A)(10 Ω) V = 20 V

6. A 10 volt battery establishes a current of 5.0 amperes in a circuit. –What is the resistance of this circuit? Example #3 I = V / R R = V / I R = (10 A) / (5.0 A) R = 2.0 Ω

7. What is a circuit? A continuous loop through which current flows from an area of high voltage to a an area of low voltage.

8. Circuit Elements – Voltage Sources batterycell

9. Circuit Elements – Resistances variable resistorfixed resistor lamp

10. Circuit Elements – Switch switch

11. Circuit Elements – Measuring Devices Measures: VOLTAGE Resistance: HIGH Connect to circuit: OUTSIDE voltmeter Measures CURRENT Resistance: LOW Connect to circuit: INSIDE ammeter

12. Proper Use of Meters 5 V 2.5 Ω 0 V 2 A 5 V 0 V 2 A 5 V NEXT

13. End of 4.2.3A