1. Ying Yi PhD Lab 3 Resistance and Ohm’s Law 1 PHYS II @ HCC

2. Current of water 2 PHYS II @ HCC

3. Average current Average current is equal to the amount of charge divided by the time interval: SI unit: coulomb/second (C/s), or the ampere (A) is the amount of charge that flows through an area A in a time interval and that the direction of flow is perpendicular to the area. 3 PHYS II @ HCC

4. Current and Voltage Measurement 4 Note that: Be sure to always start your measurements using the highest multimeter scales(say 10A and 1000V), and increase the sensitivity one scale at a time to obtain the highest accuracy without overloading the meters. PHYS II @ HCC

5. Resistance 5 Resistance is the ratio of the voltage across the conductor to the current it carries. It is a constant over a wide range of applied voltage or currents. SI unit: ohms ( Ω ) PHYS II @ HCC Q: Graph shape with Δ V as the ordinate and I as the abscissa?

6. Resistor 6 A conductor that provides a specified resistance in an electric circuit. The symbol for a resistor in circuit diagrams is a zigzag line: is called the resistivity of the material. Good electric conductor have very low resistivity. PHYS II @ HCC

7. Resistors in series The current is the same in the two resistors because any charge that flows through R1 must also flow through R2. ∆V ab + ∆V bc = ∆V ac 7 Ohm’s law PHYS II @ HCC

8. Resistors in parallel 8 PHYS II @ HCC

9. Resistors in parallel 9 The potential difference across the resistors are the same because each is connected directly across the battery terminals. ∆V= ∆V 1 = ∆V 2 Charge is conserved! I=I 1 +I 2 Ohm’s law PHYS II @ HCC

10. Objectives PHYS II @ HCC 10 Definition of the concept of electrical resistance Demonstration of the dependence of the resistance on the length, cross sectional area, and resistivity of the wire Demonstration of the equivalent resistance of resistors in series and in parallel arrangements

11. Equipment List PHYS II @ HCC 11 Resistance coils Multimeter DC supply Wire leads with alligator clips

12. PHYS II @ HCC 12 R1R1 R2R2 R3R3 R4R4

13. PHYS II @ HCC 13 I (A)V R1 V R2 V R3 V R4 0.50 1.00 1.50 2.00 CombinationI (A)V (volts) R 1 R 2 R 3 R 4 Series R 2 R 3 R 4 Series R 1 R 2 Parallel R 1 R 3 Parallel R 2 R 3 Parallel Data

14. Figures PHYS II @ HCC 14 R1 and R2 in parallel R1 and R3 in parallel

15. PHYS II @ HCC 15 R1R1 R2R2 R3R3 R4R4 R theo = ρl/A R exp 0.5503 % error Combination(Re) exp1 (Re) exp2 (Re) exp (Re) theo % error R 1 R 2 R 3 R 4 Series R 2 R 3 R 4 Series R 1 R 2 Parallel R 1 R 3 Parallel R 2 R 3 Parallel Calculations