A student is investigating the properties of a semiconducting diode. This diagram shows the circuit she builds.

Suggest why the safety resistor is required.

A student is investigating the properties of a semiconducting diode. This diagram shows the circuit she builds.

When the potential difference across the safety resistor is $1.4 \mathrm{V}$, the current in it is $20 \mathrm{mA}$. Calculate the resistance of the safety resistor.

(a) Explain what is meant by an ohmic conductor.

Sketch a graph of resistance $R$ against voltage $V$ for a wire of pure iron kept at constant temperature. Label this line $X$.

Sketch a graph of resistance $R$ against voltage $V$ for wire of impure iron, which is kept at constant temperature. Label this line $Y$.

Graph of resistance $R$ against voltage $V$ for a wire of pure iron kept at a constant temperature:

Graph of resistance $R$ against voltage $V$ for a wire of impure iron kept at a constant temperature:

Explain how the graphs would change if the wires were kept at a higher, but still constant, temperature.

The readings in this table are recorded from an experiment to measure the resistivity of silver.

Calculate the resistivity of silver.

The readings in this table are recorded from an experiment to measure the resistivity of silver.

Calculate the percentage uncertainty in each of the variables.