# Ohms Law and Resistance

Pages: 3 (784 words) Published: November 9, 2012
Aim:
To determine the relationship between the length of eureka wire, and resistivity of the wire. Hypothesis:
As the length of the wire increases, the resistance of the wire will increase. Background:
Some materials have consistent resistance at the same temperature regardless of how much voltage is applied through them, these materials are known as ‘Ohmic’ resistors. This is because they are said to obey Ohm’s law, which states that if a voltmetre is used to measure the voltage (V) of an unknown resistance (R), and an ammetre is used to measure the current (i) through the same unknown resistance, then ‘R’ would be given by R = V/i . The eureka wire used in this experiment is an ohmic resistor, so theoretically it can be used to measure the relationship between its length and resistance without other variables affecting it. Equipment:

1. 1 metre length of eureka wire
2. Power supply unit
3. 1 Voltmetre
4. 1 Ammetre
5. 1 Rheostat
6. Connecting wires
Procedure:
1. Measure and cut 1 metre of wire
2. Set up the electrical circuit as in the diagram
3. Set the rheostat at its furthest point on one end.
4. Connect the wire into the circuit at 10cm length
5. Turn the power supply on, and record the voltage and amp readings. Turn the power supply off immediately after to prevent temperature build up in the circuit. 6. Repeat step 5 twice, adjusting the rheostat to the middle position, and then the other end position. 7. Repeat steps 3-6 increasing the length of the wire 10cm at a time, up to 1 metre total length 8. Divide the voltage by the amp readings to calculate the resistance 9. Plot the wire length against the resistance

Diagram:

Results: Table showing the calculated resistance of the wire Wire Length (cm)| Resistance 1(Ω)| Resistance 2(Ω)| Resistance 3(Ω)| Average Resistance(Ω)| 100| 3| 2.9| 2.7| 2.87|
90| 2.8| 2.5| 2.2| 2.5|
80| 2.5| 2.4| 2.6| 2.5|
70| 2.2| 1.9|...