Figure 8 shows two magnets with their N poles facing each other - Edexcel - GCSE Physics - Question 5 - 2023 - Paper 2

1. The upper magnet experiences a repulsive force due to the interaction with the lower magnet's magnetic field.

2. There is a gravitational force acting downwards on the upper magnet, pulling it towards the lower magnet.

3. The forces acting on the upper magnet are balanced: the repulsive force upwards from the lower magnet and the weight acting downwards due to gravity are equal in size.

4. Thus, the upper magnet remains in equilibrium, floating above the lower magnet.

The force on the wire is directed upwards when the conventional current flows through it, as per the right-hand rule.

The force on the magnet is directed downwards, which opposes the upward force experienced by the wire.

Using the equation for the force on a current-carrying wire in a magnetic field:

$F = B imes I imes L$

Where:

• $F$ is the force on the wire (0.15 N),
• $B$ is the magnetic flux density (0.50 T),
• $I$ is the current (2.7 A),
• $L$ is the length of the wire.

Rearranging gives:

$L = \frac{F}{B \times I}$

Substituting the values:

$L = \frac{0.15}{0.50 \times 2.7}$

Calculating:

$L = \frac{0.15}{1.35} \approx 0.11 \text{ m}$