Circuits - To prove the equation: Resistance (Ω) = Potential Difference Current.

Apparatus

• 3 Power Cells
• Voltmeter
• Ammeter
• Power leads
• Bulbs with a known resistance

Method

1. Set-up a circuit in accordance to the diagram below
2. Record the amps and potential difference values in a results table, then increase the number of cells in the circuit by a value of one each time, making sure to record the amps and potential difference after each change.
3. After adding a total of  three cells to the circuit and recording the results, remove the extra cells from the circuit so that it is the same as in the diagram
4. Then increase the number of bulbs in the circuit by a value of one, and record the results after adding the cells to the circuit each time
5. Repeat steps 3 and 4 except add three bulbs to the circuit instead of two.

Results

Calculating the Gradient

Bulb 1 Gradient

Gradient of a straight line graph: m = (y2 – y1) ÷ (x2 – x1)

(y2 – y1) ÷ (x2 – x1)

(0.2875 – 0.225) ÷ (2 - 1.125)

0.0125 ÷ 0.8750

0.0143

Bulb 2 Gradient

(y2 – y1) ÷ (x2 – x1)

(0.21 – 0.15) ÷ (2.55 - 1)

(0.06 ÷ 1.55)

0.0387

Bulb 3 Gradient

(y2 – y1) ÷ (x2 – x1)

(0.155 – 0.15) ÷ (2.0 – 1.675)

(0.005 – 0.325)

-0.3200

Analysis

From looking at my results and calculating the gradient for the graph I am able to see that as the number of bulbs in my circuit increased as did the resistance, also the potential difference increased as I added more cells to the circuit, this supports my hypothesis. Therefore my results agree with my original hypothesis that was, as I increase the amount of bulbs in the circuit the resistance will increase. This was true in the majority of my results however my first result had an unusually high resistance most likely caused by a faulty lead which increased the resistance in my circuit; the bulbs may have also not had an equal resistance causing the resistance to increase in irregular patterns.

Conclusion

Although my results are not completely consistent there is a general trend that shows as the potential difference and amps in the circuit increase so does the resistance, this supports my hypothesis. I think if the experiment was to be done again then the most important aspect to be improved would be the use of good quality equipment, by using new equipment there would be less chance of having anomalous results.