RP 10: Investigate how the force on a wire varies with flux density, current and length of wire using a top pan balance.

What is the method used to investigate how the force on a current-carrying wire varies with the current in a magnetic field? (6)

- Suspend a metal rod or wire horizontally between two identical magnets so it lies perpendicular to the magnetic field.

- Zero the electronic balance with no current flowing.

- Increase the current using a variable power supply and measure the new mass reading on the balance.

- Record the current using an ammeter and repeat for a range of currents (e.g. from 0.50 A to 6.00 A in 0.50 A steps).

- Repeat each measurement twice more and calculate the mean force for each current.

- Measure the length of the wire inside the magnetic field.

What equipment is required to determine magnetic flux density using the relationship F = BIL? (7)

- Wire to suspend.

- Two stands with clamps.

- Two identical magnets.

- Weighing scales.

- Ammeter.

- Variable power supply.

- Ruler.

What does the setup used to investigate how the force on a current-carrying wire varies with the current in a magnetic field look like? (3)

What is the independent variable in the magnetic flux density experiment? (1)

The independent variable is the current flowing through the wire.

What is the dependent variable in the magnetic flux density experiment? (2)

- The dependent variable is the force on the wire.

- This is measured via mass change on the balance.

What are the controlled variables in the magnetic flux density experiment? (3)

- The controlled variables include the length of wire in the magnetic field.

- Another controlled variable is the magnetic field strength.

- Another controlled variable is the orientation of the wire.

What graph is plotted to determine magnetic flux density? (1)

Plot a graph of force (F) against current (I).

What does a graph plotted to determine magnetic flux density look like? (3)

What does the gradient of the force-current graph represent? (2)

- The gradient of the line will be equal to B × L.

- Where L is the length of the wire in the field (m) and B is the magnetic flux density (T).

How is the magnetic flux density calculated from the graph? (1)

Divide the gradient by L to find the magnetic flux density (B).

What is one safety precaution in the magnetic force on a wire experiment? (2)

- Do not touch the wire while current is flowing.

- This is because it may become hot and cause burns due to high currents.

What is one improvement to reduce uncertainty in the force on a wire experiment? (1)

Use electronic scales with a high resolution to detect the very small changes in force caused by the magnetic field.