3 (a) A student has a bar magnet, a piece of iron the same size as the magnet, and some paper clips - Edexcel - GCSE Physics Combined Science - Question 3 - 2018 - Paper 1

The student should first measure and note the position of the pointer before switching on the current in the solenoid. After switching the current on, they can measure the new position of the pointer to determine the length of the spring’s extension. Using an ammeter, the student can measure the current flowing through the solenoid and incrementally increase it for each trial. The student should calculate the force of attraction using the spring constant and extension, and then repeat the measurements with different current values to see how the attraction force varies with current size.

To calculate the energy transferred in extending the spring, we use the formula:

$E = \frac{1}{2} k x^2$

where:

• $E$ is the energy transferred,
• $k$ is the spring constant (24 N/m), and
• $x$ is the extension (0.12 m).

Substituting in these values: $E = \frac{1}{2} \times 24 \, \text{N/m} \times (0.12 \, \text{m})^2$ After calculating, the energy transferred is $E = 0.144 \, \text{J}$, which can be rounded to 0.17 J.