Magnetic Force on a Wire (AQA A-Level Physics): Revision Notes
📚Revision Notes
Magnetic Force on a Wire
Equipment
- Wire to suspend: Placed within the magnetic field.
- Two stands with clamps: To support the wire and magnets.
- Two identical magnets: To create a uniform magnetic field.
- Weighing scales: To measure the change in force (measured as mass).
- Ammeter: To measure the current in the circuit.
- Variable power supply: To adjust the current through the wire.
- Ruler: To measure the length of the wire within the magnetic field.
Note
Method
- Setup the Circuit and Zero the Balance:
- Arrange the apparatus as shown, ensuring the wire is positioned horizontally between the two magnets and can move freely within the magnetic field.
- With no current flowing, tare the balance to zero the mass reading.
- Apply Current and Record Force:
- Adjust the power supply to set the current to 0.50 A, as measured by the ammeter.
- Record the mass displayed on the balance. This change in mass reflects the downward force acting on the wire.
- Increase Current:
- Increase the current in increments of 0.50 A, repeating the measurements up to a maximum current of 6.0 A.
- For each current setting, record the mass on the balance.
- Repeat for Accuracy:
- Conduct the experiment twice more to obtain average mass readings for each current.
- Measure Length of Wire in Field:
- Use the ruler to measure the length of the wire within the magnetic field (i.e., the distance between the two magnets).
Graphs and Calculations
- Calculate Force:
- Convert each measured mass to force by using , where .
- Plot Force vs. Current:
- Plot a graph of force (y-axis) against current (x-axis).
- Draw a line of best fit. The gradient of this line represents , as per the relationship .
- Determine Magnetic Flux Density :
- Rearranging gives .
- Calculate by dividing the gradient by the length of the wire in the magnetic field.
Note
Safety
- Avoid Touching the Wire: High currents can cause the wire to heat up, which may result in burns.
- Ensure Equipment Stability: Make sure the setup is secure to prevent any components from tipping or falling due to the applied magnetic force.
Improvements and Notes
- Use a High-Resolution Scale:
- Since the forces involved are generally small, a scale with high precision will improve measurement accuracy.
- Add a Variable Resistor:
- Adding a variable resistor in series with the wire allows fine control over the current, making it easier to achieve precise current increments.
Note
Key Concepts
- Magnetic Force on a Wire: The force on a current-carrying wire in a magnetic field depends on the magnetic flux density , the current , and the length of wire in the field.
- Calculating Flux Density: By measuring force at different currents and plotting against , we can determine from the graph's gradient.
- Practical Application of : This experiment demonstrates the quantitative relationship between magnetic fields and electric currents, a fundamental concept in electromagnetism.