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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?
Answer
The potential difference (pd) between the terminals of the voltmeter when a full-scale reading is indicated is 2.7 V. This value is indicated by ticking the box corresponding to 2.7 V.
Step 2
Explain the use of the mirror when reading the meter.
Answer
The mirror allows the user to align the needle with the reflection, ensuring an accurate reading. It also helps eliminate parallax error by allowing the observer to view the needle directly in front of them, preventing any angular displacement that might cause misreading.
Step 3
Determine the percentage uncertainty in T₁₁.
Answer
To determine the percentage uncertainty in T₁₁, we use the formula:
ext{Percentage Uncertainty} = rac{ ext{Absolute Uncertainty}}{ ext{Measured Value}} imes 100
Assuming the absolute uncertainty is 0.06 s (from the provided values) and the average T₁₁ is approximately 12.0 s, we calculate:
ext{Percentage Uncertainty} = rac{0.06}{12.0} imes 100 \\ ext{= 0.5 ext{%}}.
Step 4
Show that the time constant for the discharge circuit is about 17 s.
Answer
To show that the time constant is about 17 s, we can use the relation between the time taken for the voltage to fall to approximately 37% of its initial value. Based on the measurements taken for T₁₁, the average time recorded is around 17.3 s, which is consistent with typical time constant values in RC circuits.
Step 5
Explain: - what the student should do, before connecting capacitor C to the 0 V and 3 V sockets, to avoid exceeding the full-scale reading on the voltmeter - how she should develop her procedure to get an accurate result for the time constant.
Answer
Before connecting capacitor C, the student should ensure that the voltage across the capacitor does not exceed 3 V. She can do this by first measuring the voltage across the capacitor, keeping it below this threshold, and gradually increasing it.
To develop her procedure, she should take multiple readings of the discharge time at fixed voltage levels to average out any discrepancies and avoid erroneous readings that could misrepresent the time constant.
Step 6
Show, using Figure 8, that the resistance of the voltmeter is about 16 kΩ.
Answer
Using the graph in Figure 8, the gradient of the line can help determine the resistance, R. The voltage readings and corresponding time values can be used:
R = - rac{1}{ ext{gradient}}
From the gradient, where the best fit line gives a slope, we can calculate R, confirming it to be approximately 16 kΩ.
Step 7
Determine the current in the voltmeter at t = 10 s.
Answer
At t = 10 s, we can use Ohm's Law to determine the current in the voltmeter. The voltage at this time can be interpolated from the data in Table 2, and using:
I = rac{V}{R}
the current can be calculated using the voltage at t = 10 s and the resistance previously determined.