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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 exceed... 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 is indicated by ticking the corresponding box.
Step 2
Explain the use of the mirror when reading the meter.
Answer
The mirror serves to ensure that the needle is properly aligned with the scale, reducing errors due to parallax. It allows the user to see their reflection in the mirror, indicating that they are at the right angle when taking a reading. This minimizes any misreadings that might occur if the observer is not looking directly at the scale.
Step 3
Determine the percentage uncertainty in Ti.
Answer
To calculate the percentage uncertainty in Ti, use the formula:
ext{Percentage Uncertainty} = rac{ ext{absolute uncertainty}}{ ext{measured value}} imes 100
Using the average time Ti of 12.04 s:
Absolute uncertainty is 0.06 s (for instance). Thus:
ext{Percentage Uncertainty} = rac{0.06}{12.04} imes 100 \\ ext{Percentage Uncertainty} \\ ext{is approximately } 0.50\%
Step 4
Show that the time constant of the discharge circuit is about 17 s.
Answer
The time constant (τ) for an RC circuit is given by:
From experimental results, we can deduce that:
- Average time measured (T) is approximately 17.31 s.
- The expected relationship can be tested by relating the changes in voltage to the rates of discharge, thus showing that the time constant fits.
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 the voltmeter's range. She should measure the voltage across the capacitor with a separate voltmeter. To develop her procedure for accurate timing, she could take multiple readings at different discharge voltages and calculate the average value, ensuring consistent timing without exceeding the maximum range.
Step 6
Show, using Figure 8, that the resistance of the voltmeter is about 16 kΩ.
Answer
Using the data plotted in Figure 8, calculate the gradient of the line. Using the equation for resistance, the relationship can be derived as: rac{V}{I} = R From the graph, you can extract slope values corresponding to the voltmeter and determine the resistance. For instance, if the voltage reading is consistently around 16.1 kΩ, it supports the conclusion.
Step 7
Determine the current in the voltmeter at t = 10 s.
Answer
To find the current in the voltmeter at t = 10 s, use the formula:
I = rac{V}{R} Assuming that at t = 10 s the voltage is below 14 V and using R approximately equal to 16 kΩ, a calculation will yield:
I = rac{V(t=10)}{16000} Ensuring units align can lead to the final current value.