A student uses plotting compasses to investigate the magnetic field between the poles of two bar magnets - Edexcel - GCSE Physics: Combined Science - Question 3 - 2021 - Paper 1

To determine the shape of the magnetic field using one plotting compass, the student should:

1. Place the plotting compass at a point near one of the magnets (close to the N-pole).
2. Observe the direction of the compass needle and mark the point on the paper.
3. Move the compass to another point (further away) and again mark the direction of the needle.
4. Repeat this process at various points to create a series of directional markings, which can then be connected with a smooth curve to illustrate the magnetic field lines.
5. Ensure to note that the compass should be placed in different positions around the magnet to map the complete field.

To calculate the value of K, we use the formula given:

$F = \frac{K}{d^2}$ Given that the force, F = 1.2 N, and the distance, d = 4.0 cm = 0.04 m, we rearrange the formula:

$K = F \times d^2$ Substituting the values:

$K = 1.2 \times (0.04)^2$

Calculating:

$K = 1.2 \times 0.0016 = 0.00192$ The value of K is 0.00192 N m².

The unit for K is N m² (Newtons times meters squared).

When the N-pole of one magnet faces the S-pole of the other magnet, the force between them will be attractive. This will generally result in a stronger force than the repulsive force when the N-poles face each other. However, since K remains constant, the exact magnitude of the force can only be determined through calculations involving the specific distance used.