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Figure 10 shows a partly-completed circuit used to investigate the emf ε 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 ε and the internal resistance r of a power supply. The resistance of P and the maximum resista... show full transcript
Worked Solution & Example Answer:Figure 10 shows a partly-completed circuit used to investigate the emf ε 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
To complete Figure 10, the following components should be included in the circuit:
- Ammeter (A): Connect in series with the components to measure current. The ammeter should be placed in line with the power supply and the resistor P.
- Voltmeter (V): Connect in parallel across the power supply to measure the potential difference (pd). Ensure that the voltmeter is connected with correct polarity, positive to the positive terminal of the power supply.
Step 2
Describe a procedure to obtain valid experimental data using your circuit.
Answer
- Setup the Circuit: Connect the components as per the completed Figure 10 with the ammeter and voltmeter appropriately connected.
- Measure Initial Current: Start with one 22 Ω resistor and record the current I using the ammeter.
- Add Resistors: Gradually add more 22 Ω resistors in series and record the current I each time.
- Repeat Measurements: Ensure each measurement is repeated for reliability and consistency.
- Record Consistent Measurements: Record the values of current and the number of resistors in a table for further analysis.
Step 3
Describe how these data are processed to obtain ε and r by a graphical method.
Answer
- Graph Plotting: Plot the graph of rac{1}{I} against rac{n}{22} as shown in Figure 12.
- Determine Gradient and Intercept: From the graph, determine the gradient and the y-intercept. The gradient corresponds to rac{ε}{22} and the intercept gives the value of r.
- Use Linear Relationships: Solve for ε using the relationship found in the gradient, and deduce r from the vertical intercept value on the graph.
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, using the equation derived earlier: rac{22}{n} = rac{ε}{I} - r and considering the values of ε and r deduced, substitute n = 4 to calculate I. Thus, the calculated current I should provide approximately 0.25 A.
Step 6
Deduce, for the circuit shown in Figure 13, the potential difference (pd) across the power supply.
Answer
For the circuit with four resistors (each 22 Ω) connected:
- Calculate Total Resistance: The total resistance R for four resistors in series is:
- Apply Ohm's Law: Using Ohm's Law, the potential difference (pd) across the power supply can be calculated as:
Step 7
Step 8
Suggest which additional values of n should be used.
Answer
To provide sufficient data points for n = 1 and n = 14:
- Suggested Values: Use n = 2, n = 3, and n = 5 to populate the graph adequately.
- Justification: These values will ensure a smooth linear graph, aiding in the visibility of the trends in the experimental data.
Step 9
Show on Figure 14 the effect on the plots for n = 1 and n = 14.
Answer
On Figure 14, the plots will likely shift based on a change in resistance.
- Mark the point for n = 1 accordingly along the x-axis representing rac{1}{n} and an appropriate value along the y-axis.
- For n = 14, mark a new point that reflects the alteration made by the 27 Ω resistance, leading to a lesser slope compared to the previous θ.