Question

A. Describe what would happen to the electric current if the magnet moved very quickly through the cardboard tube.

B. Describe how you could test how the speed of the magnet affects the amount of current produced by the coil.

Answer 1

A.
If the magnet is moved very quickly through the tube, the magnetic flux through the coil changes more rapidly. By Faraday’s law that faster change produces a larger induced emf, so a larger (stronger) induced current flows while the magnet is passing the coil. The pulse of current will be higher in magnitude but shorter in duration. The current’s direction still follows Lenz’s law (it will reverse when the magnet passes out of the coil).

B.
A controlled experiment you can do:

What you need
- Cardboard tube with the same coil of wire fixed in place
- The same magnet for every trial
- An ammeter (or better: a voltmeter/oscilloscope or data-logger across a known resistor) to measure induced current/voltage
- A way to vary and measure magnet speed (see methods below)
- Stopwatch or light gates for timing, tape measure, clamp/stand
- Notebook for data and graphing

Procedure (one clear method)
1. Assemble the coil and connect it in series with the ammeter (or connect a known resistor across the coil and measure voltage with an oscilloscope/voltmeter).
2. Keep all variables constant except the magnet speed: same magnet, same coil turns, same alignment and release point relative to the tube.
3. Vary magnet speed by changing drop height (or pull speed using a motor/pulley, or a ramp of different angles). If using drop heights, mark several release points above the tube.
4. Measure the magnet speed just before it enters the coil:
- Best: use two light gates a known distance apart and record the time between them to calculate velocity.
- Simpler: measure the distance fallen and compute speed from free-fall (v = sqrt(2gh)) if friction/air resistance are negligible.
5. For each chosen speed, release the magnet and record the peak current (or peak voltage) produced. Repeat each speed several times and average the peak values.
6. Plot peak current (or peak voltage) versus magnet speed.

Expected result and notes
- You should see larger peak currents at higher magnet speeds. For moderate speeds the peak current is roughly proportional to speed.
- Keep trials repeatable, average repeats, and watch for experimental errors (timing errors, misalignment, coil resistance changes, contact/bounce). An oscilloscope gives the clearest measurement of peak and pulse duration.