This question is about using a digital balance to investigate the force on a wire placed in a magnetic field when there is an electric current in the wire - AQA - A-Level Physics - Question 1 - 2018 - Paper 3

The direction of the horizontal uniform magnetic field can be determined using the right-hand rule. If the current in the wire runs from terminal P to terminal Q, the magnetic field will be directed perpendicular to the current. If the wire is oriented horizontally and the current flows from left to right, the magnetic field will point upward.

Using the formula provided, we can calculate the magnetic flux density.

If we take a force $F$ exerted on the prism, where $I$ is the current and $L$ is the effective length of the wire within the magnetic field:

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

In this case, sufficient data from the graph in Figure 4 will be necessary to find $F$ and $I$. Let's say the force measured for a specific current is recorded to be 0.2 N with $I$ being 4 A and $L$ being 1 m. Then it would be:

$B = \frac{0.2}{4 \cdot 1} = 0.05 \, T$

In row 1, the effect of the force acting on the wire due to the horizontal uniform magnetic field will increase, and we would tick the box for 'increased'. In row 2, as the wire pushes against the prism, we would tick the box for 'increased' as well.

To complete the circuit in Figure 6, connect wire X from the terminal block to one end of wire Y. Both wires should continue back to the power supply so that the current can flow through both wires without interruption. Ensure both wires have the same direction of current by linking them in parallel to the power supply.

To find the current $I$, the student could use an ammeter connected in series with the circuit. By varying the resistance or using a variable resistor, the student can measure the current reading on the ammeter. That reading will give the magnitude of the current $I$ passed through wires X and Y.