(b) use of appropriate digital instruments, including electrical…

The idea

This practical skill requires you to select and correctly operate digital instruments, especially electrical multimeters, to obtain measurements. You must choose the right instrument for the quantity: a multimeter set to voltage for potential difference, current for current, or resistance for resistance. When using a multimeter, insert the leads into the correct sockets, select the appropriate range (auto or manual), and connect in parallel for voltage or in series for current. For example, to measure the current through a resistor, break the circuit and connect the multimeter in series, ensuring the range exceeds the expected current. You should also consider accuracy, resolution, and zero error. The skill is assessed in practical examinations where you must demonstrate correct setup and reading.

What earns the marks

• Select a digital instrument appropriate to the quantity being measured, such as a multimeter for electrical measurements.
• Connect a multimeter in series to measure current and in parallel to measure potential difference.
• Choose a suitable range so that the reading is within the display limits and gives appropriate precision.
• Read and record the value with the correct unit and an appropriate number of significant figures.
• Check for and account for zero error or offset before taking readings.

Common mistakes and how to put them right

• Connecting a multimeter in parallel to measure current.

  Put it right: Connect it in series.

• Using a range that is too low, causing an overload reading.

  Put it right: Start with a higher range and decrease for better resolution.

• Ignoring the need to zero a multimeter before use.

  Put it right: Check that it reads zero when the leads are not connected or when appropriate.

• Recording a reading without units or with too many decimal places.

  Put it right: Include the correct unit and match significant figures to the instrument resolution.

Exam tips

• Always state the instrument and the setting used, for example 'digital multimeter set to 200 mA d.c.'.
• When describing a circuit, specify whether the meter is in series or parallel and justify the choice.
• Practise reading a multimeter display from diagrams or photographs to avoid misreading the scale or range.