Physics · Electricity · Magnetism / Principles and Exploration
Electromagnetic induction — principles and investigation
The mere presence of a magnet near the coil does not cause current to flow continuously. Observe the moment when the magnetic flux changes by changing the moving direction, speed, pole, and number of coil turns of the magnet. Connect the magnitude of the induced electromotive force to the speed of change, and the direction to the action that hinders the change.
How does it work?
The faster the movement and the more turns there are, the greater the electromotive force. Current interferes with changes in magnetic flux.
ε = −N ΔΦ/Δt · I = ε / 10 Ω
Try this investigation
- When you run it, the magnet passes through the coil. If you move the magnet or position slider while running, it changes to manual movement. In a stopped magnet, the electromotive force becomes 0 V. +The current is counterclockwise when viewed from the left side where the magnet is.
- Press the standard conditions button, run it, and record each measurement value.
- Use automatic movement to record standard conditions. Manual records are manually marked in the table. If you just flip the poles, the signs of magnetic flux and electromotive force change. If the number of turns is doubled, the maximum electromotive force is doubled.
Interpreting your results
How does the induced-current direction change when the magnet moves away rather than toward the coil?
As the magnetic flux increases and decreases, the direction of the current changes according to Lenz's law.
Assumptions and limitations
The magnetic flux is approximated on axis as Φ=−pole sign×5×10⁻⁵/[1+(x/0.12)²]^(3/2) Wb. The coil resistance is 10 Ω, and self-induction and friction are omitted. Manual movement is limited to 3 m/s and observed for 4 s. The needle saturates at ±0.2 V.