Ohms Law

Bernard Ndegwa Friday June 5, 2009 Lab 2: Ohms Law Objective The objective of this lab is to investigate the relationship between the three variables involved in Ohm's Law - Current, Voltage and Resistance. We shall also gain hands on skills in building electrical circuits.

Theory and calculations. In this lab, we will construct a simple circuit using a single known resistance, R. Then we will use an ammeter to measure the current, I, through the resistance and a voltmeter to measure the potential difference, V, across the resistance. With this data, we can check the validity of Ohm's Law (V = IR) in the circuit. Equations Resistance = Voltage/Current R = V/I Voltage = Current * Resistance V=I*R Current = Voltage/Resistance I = V/R

Results. Variation of current with voltage. Table shows the results. Reading

Voltage(v)

Current(i)

Voltage(v)

Current(i)

1

3.0

0.138

2.25

0.1

2

2.5

0.118

1.82

0.08

3

2.0

0.099

1.45

0.06

4

1.5

0.065

1.03

0.04

5

1.0

0.038

0.64

0.02

Slope of graph 1 = 21.522 ohms. Slope of graph 2 = 23.255 ohms.

Thus we can calculate the percent error which is: [(21.522-22.000)/22.00]*100=-2.172 % [(23.255-22.000)/22*100]=5.7% Unknown resistance. Reading 1 2 3 4 5 6 7

Computed current 3.38 3.38 3.46 3.43 3.50 3.70 3.90

Voltage 2.37 2.03 1.73 1.07 1.05 0.75 0.39

Current 0.7 0.6 0.5 0.4 0.3 0.2 0.1

The graph shows that the average resistance for the unknown resistor was 3.279 ohms while the calculated resistance ranged from 3.90 to 3.38 ohms. Error Analysis. Sources of error for this experiment include resistance of the wire, internal resistance of the battery and current consumption of the meters. However the error percent was less than 5% thus the experiment was pretty accurate. The data demonstrates how important ohms law is to understanding the relationship between current, resistance and voltage. Conclusion. The relationship between current, voltage and resistance in a metallic conductor is given by ohms law. It states that if the temperature and other physical conditions of a metallic conductor are unchanged the ratio of the potential difference across the conductor (v) to the current (i) is a constant. This constant ratio (R) is the resistance of the conductor. R= V/I