Electromagnetic Induction

The question behind the experiment

A strong magnetic field does not necessarily produce an induced voltage. This course investigates changes in magnetic flux through a coil and connects those changes to the electrical signal. Predict what happens when a magnet approaches, stops, passes through, or reverses direction. Keep the magnet's position separate from its velocity. A coil can have substantial flux at a position where the flux is momentarily not changing, so the largest flux and largest voltage need not occur together.

Plan a useful comparison

Choose a controlled comparison involving magnet motion, coil turns, field strength, coil area, or orientation. Keep the remaining conditions explicit. In a uniform field, flux depends on the field component perpendicular to the coil area. In the magnet-coil setup, the field varies across the area, so flux is accumulated over the coil surface rather than determined by one field arrow. Distinguish flux per turn from flux linkage when comparing coils with different numbers of turns.

Connect the observation to the model

Follow the flux-time and voltage-time graphs for the same motion. Faraday's law relates induced electromotive force to the rate of change of flux linkage. A steeper change can give a larger voltage, while a plateau in flux gives no induction from that change. For an open circuit, interpret the area under the electromotive-force graph as a linkage change, with sign convention retained. Compare entry and exit parts of the motion rather than describing the entire pass with one voltage sign.

Interpret the result carefully

Use Lenz's law to predict the direction of induced current: the induced effect opposes the flux change. This is different from saying it always opposes the original magnetic field. Reversing the motion at the same position reverses the change, and reversing the magnet reverses the relevant field direction. Connect each prediction to the coil's winding and electrical reference direction. A sign drawn on a graph has meaning only after those conventions have been specified for the apparatus.

Build an explanation from your evidence

Choose the instrument that answers your question. An open-circuit voltage sensor measures an induced electromotive force in the course comparison, while a closed circuit includes coil resistance and load effects. A galvanometer can also respond with mechanical inertia rather than instantaneously tracing the changing signal. Record the connection and instrument type with your measurements. Interpret a smaller terminal voltage through the selected circuit instead of assuming that the magnetic-flux change must have been smaller in that run.

A reference case from this course

For the reference small coil with 100 turns, the specified wire length is 4.223055 m and coil resistance is 1.436917 Ω. These apparatus parameters help explain why a closed-circuit reading can differ from an open-circuit comparison. They describe that coil geometry and wire, not every coil with the same turn count.

Keep the investigation reproducible

Before changing the setup, write a prediction that names the measured quantity and the expected direction of change. Retain the original trial as a reference. Record the apparatus conditions, units, and whether you used Ideal or Real lab mode. If the selected activity includes seeded variation, keep the seed and run identity with the result so another comparison does not silently mix different conditions.

Separate the observation from its explanation. A reading or a counted object belongs in the evidence; the relationship you use to interpret it belongs in the reasoning. When a result differs from the reference case, check the settings and measurement procedure before deciding that the model relationship has failed. Describe a specific source of uncertainty and where it enters your calculation. Finish with a claim supported by the recorded comparison, and identify an additional trial that could distinguish your explanation from an alternative.

Continue the comparison

Explore the source field in Magnetic Fields & Currents and the circuit measurements in Ohm’s Law. Keep flux change, induced electromotive force, and measured terminal voltage separate when combining the explanations.