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Planning at A2: apparatus, data loggers and calibration

Edexcel IAL Physics · WPH16 Practical Skills in Physics II

At A2, a plan must name the most appropriate apparatus and justify it. Data loggers and calibration come up often.

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Naming apparatus properly

Give details that show you have thought about the measurement:

'a metre rule with mm divisions, clamped vertically' rather than 'a ruler';
'vernier calipers (0.1 mm) using the internal jaws' for the inside diameter of a pipe; a micrometer cannot do this;
'a top-pan balance reading to 0.01 g';
'a 2 m length of wire', 'a 30 cm ruler', 'a GM tube connected to a counter'.

Choose the instrument whose range covers the values and whose resolution gives a small percentage uncertainty.

Data loggers

Give reasons linked to the context. Creditworthy reasons include:

a high sampling rate, for events that are too fast to read by hand (collisions, capacitor discharge with small RC);
simultaneous readings of two or more quantities;
readings over long periods without a person present;
no reaction-time error, and data stored for graphing.

'It is more accurate' or 'it records automatically' on its own is not enough. 'Continuously' suggests a long duration, not a high sampling rate. The sampling interval is 1 / sampling rate.

Calibration

Calibrating means checking an instrument against known values and correcting it:

a thermometer in melting ice (0 °C) and boiling water (100 °C at standard pressure);
a balance with a known standard mass;
a thermistor circuit against a thermometer (core practical 12), giving a calibration curve.

Calibration reduces systematic error.

Worked example

A collision lasts about 0.05 s. Why use a force sensor and data logger sampling at 1000 Hz?

Sampling interval = 1 / 1000 = 0.001 s
Number of readings during the collision = 0.05 / 0.001 = 50
Far too fast to read by hand, and the logger records force and time together.

Answer: About 50 readings during the collision, enough to draw the force-time graph

Key idea: Name apparatus with useful details (range, resolution, size). Justify data loggers by high sampling rate, simultaneous readings or long duration. Calibrate against known values to remove systematic error.

Check yourself

A data logger samples at 500 samples per second. What is the time between samples, in ms?
Show answer
2 ms. Interval = 1 / 500 s = 0.002 s = 2 ms.
A capacitor discharges over about 0.25 s. How many readings does a logger sampling at 1.0 kHz take in this time?
Show answer
250 readings. 0.25 x 1000 = 250 readings.
Which is a creditworthy reason for using a data logger to record the p.d. across a discharging capacitor with a time constant of 0.1 s?
- The p.d. changes too quickly to read by hand, and the logger has a high sampling rate
- Data loggers are always more accurate
- It records automatically
- It removes the need for a resistor
Show answer
The p.d. changes too quickly to read by hand, and the logger has a high sampling rate. Link the reason to the speed of the change.
Which apparatus is most appropriate for the internal diameter of a 15 mm pipe?
- A micrometer screw gauge
- A metre rule
- A protractor
- Vernier calipers, using the internal jaws
Show answer
Vernier calipers, using the internal jaws. Only calipers have internal jaws; examiners noted 'micrometer' as a common error.
How can a thermometer be calibrated?
- Take repeat readings and average them
- Check its readings in melting ice and boiling water
- Use a smaller beaker
- Read it at eye level
Show answer
Check its readings in melting ice and boiling water. Comparing with known fixed points corrects systematic error.
Give two reasons for using a data logger to record the temperature of a river overnight.
Show answer
It can take readings over a long period with no one present, at regular intervals, and stores the data for analysis.. Reasons must fit the context: long duration and stored regular readings.
What kind of error does calibration reduce?
- Random error
- Systematic error
- Reaction-time error
- Anomalous readings
Show answer
Systematic error. Calibration corrects a consistent offset or scale error.

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Last updated 8 November 2026. Spotted a mistake? Tell us.