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

Current of water 2 PHYS HCC

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 HCC

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 HCC

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 HCC Q: Graph shape with Δ V as the ordinate and I as the abscissa?

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 HCC

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 HCC

Resistors in parallel 8 PHYS HCC

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 HCC

Objectives PHYS 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

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

PHYS HCC 12 R1R1 R2R2 R3R3 R4R4

PHYS HCC 13 I (A)V R1 V R2 V R3 V R 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

Figures PHYS HCC 14 R1 and R2 in parallel R1 and R3 in parallel

PHYS HCC 15 R1R1 R2R2 R3R3 R4R4 R theo = ρl/A R exp % 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