Photo AI
Figure 10 shows a partly-completed circuit used to investigate the emf £ and the internal resistance r of a power supply - AQA - A-Level Physics - Question 3 - 2020 - Paper 3
Question 3
Figure 10 shows a partly-completed circuit used to investigate the emf £ and the internal resistance r of a power supply. The resistance of P and the maximum resist... show full transcript
Worked Solution & Example Answer:Figure 10 shows a partly-completed circuit used to investigate the emf £ and the internal resistance r of a power supply - AQA - A-Level Physics - Question 3 - 2020 - Paper 3
Step 1
Complete Figure 10 to show a circuit including a voltmeter and an ammeter that is suitable for the investigation.
Answer
A valid circuit should include an ammeter connected in series with the power supply and the unknown resistance R. The voltmeter should be connected in parallel with the unknown resistance P. Ensure that there are appropriate connections to measure the voltage across P and the current flowing through the circuit.
Step 2
Describe a procedure to obtain valid experimental data using your circuit.
Answer
- Set up the circuit as indicated in Figure 10, ensuring the ammeter and voltmeter are connected correctly.
- Connect a known resistor (22 Ω) in series with the power supply and measure the current (i) flowing through the circuit.
- Gradually add more 22 Ω resistors in series, recording the current (i) for each configuration.
- Repeat the measurements several times to ensure accuracy and reliability.
- Record the corresponding voltage across the known resistors using the voltmeter.
Step 3
Describe how these data are processed to obtain £ and r by a graphical method.
Answer
To process the data:
- Use the recorded current (i) and the number of resistors (n) to compute the corresponding values of the voltage across the power supply using the formula: rac{22}{n} = rac{£}{i} - r
- Plot the values of rac{1}{i} on the y-axis against rac{1}{n} on the x-axis.
- Determine the gradient (m) of the line obtained from the graph, which will give the internal resistance r. The intercept will provide data to calculate the emf £.
Step 4
Step 5
Show, using Figure 12, that the current in the power supply is about 0.25 A.
Answer
From the graph in Figure 12, identify the slope alongside the calculated values when n = 4 (four resistors). Using the formula I = rac{£}{R + r}, calculate the current by substituting in the effective resistance considering four 22 Ω resistors.
Step 6
Deduce, for the circuit shown in Figure 13, the potential difference (pd) across the power supply and r.
Answer
With four resistors, the equivalent resistance is . If the measured current is 0.25 A, apply Ohm's Law: . The internal resistance r can be calculated as well by using the previously gathered data regarding the emf £, previously found to be about 1.6 V.
Step 7
Suggest which additional values of n should be used.
Answer
It would be beneficial to include additional values of n such as 2, 3, and 5 to provide a more comprehensive set of data points that can be effectively plotted for the relationship established in Figure 14. This allows for clearer trend observation and better interpolation.
Step 8
Show on Figure 14 the effect on the plots for n = 1 and n = 14.
Answer
On Figure 14, extending the plot points for n = 1 and n = 14 demonstrates the effect of using 27 Ω resistors instead of 22 Ω resistors across the graph. Since the resistance is higher, the slope of the graph will appear steeper, potentially reducing the overall current value plotted against the previous 22 Ω graphs.