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

The mirror is used to ensure accurate reading of the needle position. It reflects the needle, allowing the user to align their viewpoint directly in front of it, thereby reducing parallax error. This ensures that the scale is read correctly without distortion.

The percentage uncertainty can be calculated using the formula:

ext{Percentage Uncertainty} = rac{ ext{Absolute Uncertainty}}{ ext{Mean}} imes 100

For the calculated mean T_i values, if the average is taken, we find the absolute uncertainty based on the range of readings.

For this question, we write the discharge formula:

$V(t) = V_0 e^{-t/RC}$

where V_0 is the initial voltage, R is the resistance, C is the capacitance, and V(t) is the voltage at time t. By analyzing the data and time measurements collected, we can apply the time constant to show it approaches 17 s.

Before connecting capacitor C, the student should ensure that the voltage across the meter does not exceed its maximum rating (3 V and 15 V) by using a known resistor or a switch to control the input voltage to avoid damage.

For developing her procedure, she should take multiple readings at different voltages, calculate the average of these readings, and carefully note the time taken for the voltage to fall, ensuring consistent starting conditions.

1. The student may have chosen these values to ensure a wide range of data that adequately represent the discharge curve while staying below the maximum reading limit of the meter.
2. Selecting values that are evenly spaced allows for a clearer analysis and helps in identifying patterns or discrepancies in the results.

To calculate the resistance, the student can use Ohm's law in conjunction with the graph from Figure 8. From the linear relationship presented in the graph, the gradient can be analyzed, preferably plugging values into the formula derived from the graph equation, showing that:

R = -rac{1}{ ext{gradient}}

This approach leads to the conclusion of the voltmeter resistance being approximately 16 kΩ.

The current can be calculated using:

I = rac{V}{R}

where V is the voltage at t = 10 s (as read from the data or graph) and R is the previously calculated resistance. By substituting these values, the student can find the current in the voltmeter.