Magnetic Flux Linkage (AQA A-Level Physics): Revision Notes

Method

1. Set Up the Coils:

• Mount the large circular coil vertically on a stand. Position the search coil at the centre of the circular coil, initially parallel to it. Place the protractor card beneath the coils to measure the angle accurately.
• Connect the circular coil to the AC supply and the search coil to the oscilloscope as shown in the diagram.

2. Initial Measurement:

• Turn on the AC supply. Adjust the oscilloscope's voltage sensitivity and time base settings for clear readings. Record the peak-to-peak voltage of the induced AC voltage in the search coil.

3. Vary the Angle:

• Tilt the search coil to change the angle $\theta$ between its plane and that of the circular coil. Increase $\theta$ by $10°$ increments, up to a maximum of $90°$, using the protractor to measure each angle.
• For each angle, record the peak-to-peak voltage displayed on the oscilloscope.

4. Repeat for Accuracy:

• Repeat the experiment twice more to obtain average emf values at each angle.

Safety

• Minimal Risks: This practical has minimal safety concerns, but ensure the setup is stable to avoid accidental movement of the coils.

Key Concepts

• Magnetic Flux Linkage: The emf induced in the search coil depends on the rate of change of magnetic flux linkage, which varies with $\cos(\theta)$.
• Relationship to Angle: This experiment verifies that the emf is maximised when the coil is parallel to the magnetic field (i.e., $\theta = 0°$) and decreases as the angle increases, reaching zero when the coil is perpendicular to the field ( $\theta = 90°$).
• Application of Faraday's Law: This practical demonstrates how changing magnetic fields induce emf in a coil, as described by Faraday's Law of Induction.