The circuit on the right is used to demonstrate Ohm's law - Leaving Cert Physics - Question 9 - 2019

A meter V is known as a voltmeter, which measures the electrical potential difference (voltage) across two points in a circuit in volts (V).

The correct graph that shows Ohm's law being obeyed is Graph 1, which illustrates a straight line through the origin. This indicates a direct proportionality between current (I) and voltage (V), confirming that resistance remains constant, as per Ohm’s law, where $V = I \cdot R$.

For resistors in parallel, the total resistance (R_total) is calculated using the formula:

$\frac{1}{R_{total}} = \frac{1}{R_1} + \frac{1}{R_2}$

Substituting the values: $\frac{1}{R_{total}} = \frac{1}{5 \Omega} + \frac{1}{4 \Omega}$

Calculating: $\frac{1}{R_{total}} = 0.2 + 0.25 = 0.45$

Thus, $R_{total} = \frac{1}{0.45} \approx 2.22 \Omega$

Using Ohm's law, we can calculate the current (I) in the circuit with:

$I = \frac{V}{R_{total}}$

Given that the voltage (V) is 12 V and the total resistance is approximately 2.22 \Omega:

$I = \frac{12 V}{2.22 \Omega} \approx 5.4 A$

The wire labelled A is the earth wire, usually colored green/yellow.

The wire labelled B is the live wire, typically colored brown.

The function of the fuse is to protect the circuit from overload by breaking the circuit if the current exceeds a safe level, thereby helping to prevent fires.

One of the devices is a circuit breaker (e.g., RCD, MCB, ELCB).