An analogue voltmeter has a resistance that is much less than that of a modern digital voltmeter - AQA - A-Level Physics - Question 3 - 2021 - Paper 3
Question 3
An analogue voltmeter has a resistance that is much less than that of a modern digital voltmeter.
Analogue meters can be damaged if the full-scale reading is exceede... show full transcript
Worked Solution & Example Answer:An analogue voltmeter has a resistance that is much less than that of a modern digital voltmeter - AQA - A-Level Physics - Question 3 - 2021 - Paper 3
Step 1
What is the potential difference (pd) between the terminals of the voltmeter when a full-scale reading is indicated?
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Answer
The correct answer is 2.7 V. This represents the maximum voltage the voltmeter can measure in the sensitive range.
Step 2
Explain the use of the mirror when reading the meter.
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Answer
The mirror helps in aligning the pointer of the voltmeter with the scale to avoid parallax error. When viewed from directly in front, the reflection shows the exact position of the needle, ensuring accurate readings.
Step 3
Determine the percentage uncertainty in T₁ₗ.
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Assuming the measurements are consistent, the calculation would yield the result based on the spread of the times recorded.
Step 4
Show that the time constant for the discharge circuit is about 17 s.
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Answer
The time constant (τ) for the discharge of a capacitor through a resistor is given by:
au=RimesC
Given the discharge readings, the mean value of T₁ₗ can be used to validate that τ approximates 17 s.
Step 5
Explain: what the student should do to avoid exceeding the full-scale reading on the voltmeter.
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Answer
The student should ensure that the voltage across capacitor C does not exceed the full-scale limit of the voltmeter by using a suitable resistor in series or initially connecting to a lower voltage range.
Step 6
Explain: how she should develop her procedure to get an accurate result for the time constant.
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Answer
To develop an accurate procedure, the student should repeat measurements multiple times for the same voltage levels, averaging the time for each discharge cycle and controlling environmental factors as much as possible.
Step 7
Show, using Figure 8, that the resistance of the voltmeter is about 16 kΩ.
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Answer
Using the graph from Figure 8, determine the gradient, which corresponds to the resistance by the relationship:
R = - rac{1}{ ext{gradient}}
Ensuring data points used are within the appropriate range will yield a resistance of approximately 16 kΩ.
Step 8
Determine the current in the voltmeter at t = 10 s.
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Answer
The current through the voltmeter can be calculated using Ohm's law:
I = rac{V}{R}
Where V is the voltage across the voltmeter and R is the resistance found earlier.
