In an experiment to investigate the internal resistance of a DC power supply, a student records the current $I$ and the terminal potential difference $V$ across the power supply as the external resistance is varied.

The recorded data is shown in the table below:

\begin{array}{|c|c|} \hline \text{Current } I / \text{A} & \text{Terminal Potential Difference } V / \text{V} \\ \hline 0.15 & 2.65 \\ \hline 0.30 & 2.35 \\ \hline 0.45 & 2.05 \\ \hline 0.60 & 1.75 \\ \hline 0.75 & 1.45 \\ \hline \end{array}

Use the data to calculate the gradient $M$ of the graph of $V$ ( $y$ -axis) against $I$ ( $x$ -axis). Show your working.

The internal resistance $r$ is equal to the magnitude of the gradient $M$ . Write down the value of $r$ to a suitable number of significant figures and include the appropriate unit.

Suggest one practical reason why the student should not connect the circuit using extremely short lengths of the external resistance wire (which corresponds to very low external resistance).

Instead of varying the length of a resistance wire, a variable resistor can be used. Describe the standard circuit symbol for a variable resistor.

The recorded data is shown in the table below:

\begin{array}{|c|c|} \hline \text{Current } I / \text{A} & \text{Terminal Potential Difference } V / \text{V} \\ \hline 0.15 & 2.65 \\ \hline 0.30 & 2.35 \\ \hline 0.45 & 2.05 \\ \hline 0.60 & 1.75 \\ \hline 0.75 & 1.45 \\ \hline \end{array}

Use the data to calculate the gradient $M$ of the graph of $V$ ( $y$ -axis) against $I$ ( $x$ -axis). Show your working.

The internal resistance $r$ is equal to the magnitude of the gradient $M$ . Write down the value of $r$ to a suitable number of significant figures and include the appropriate unit.

Suggest one practical reason why the student should not connect the circuit using extremely short lengths of the external resistance wire (which corresponds to very low external resistance).

Instead of varying the length of a resistance wire, a variable resistor can be used. Describe the standard circuit symbol for a variable resistor.

4.2.3a Electromotive force

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4.2.3a Electromotive force

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4.2.3a Electromotive force

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4.2.3a Electromotive force Questions