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ScienceHigh schoolKey Stages 4 and 5

How to teach electromagnetic induction

Electromagnetic induction makes current only while the magnetic field through a coil changes. In this free lab activity, students find that out from their own simulator readings, and Sparky sends a student who thinks a still magnet makes current back to their 0 mA run.

Jemel Fanfan

Jemel Fanfan | Founding Member at Flint

Title card reading 'How to teach electromagnetic induction', next to three cards from a student's chat: his run log showing +6.0 mA while the magnet moved and 0 mA once it sat still inside the coil, Sparky asking what the meter read in that row, and the phone charging at 400 turns and 120 RPM.

Why this matters

A student who sees the meter jump as a magnet goes into a coil will often decide that the magnet makes the current. The same student's next reading, with the magnet sitting still inside the coil, is 0 mA. If nobody asks about that 0, the student writes "magnets make electricity" on the lab sheet, and the teacher has to wait for quiz day to find out.

Diego checks his own 0 mA reading, then charges the phone

Diego rides his bike to school. He knows magnets pull on metal, and he hasn't studied induction yet.

Every student in the class gets the same Bike Generator Lab in Sparky's first message: a magnet, a coil, a meter, a compass, a phone to charge and a run log that records every move. Everyone gets the same first task and the same first question. The rest of the chat is Diego's own: his readings, his answers, and which question Sparky asks next. Diego is an example student, and his chat is shortened.

Sparky uses Diego's bikeSparky sends Diego back to his own readingsSparky asks a harder question after a right answer
D

Diego

Interest: Rides a bike to schoolStarting point: Knows magnets pull on metalGets stuck: Thinks a magnet inside the coil makes current

Sparky

Hi! Your goal is to charge a phone with a generator you build in this lab. Start here: push the magnet into the coil and leave it sitting there. What does the meter read while it moves, and what does it read once it stops? Also, how do you get to school?
Flint's Bike Generator Lab as it opens: a meter reading 0 mA wired to a copper coil, a red and blue bar magnet on a track to the left of the coil, a compass above the coil pointing north, a phone that reads Not charging 0%, buttons for Push in, Pull out and Flip magnet, a Slow, Medium and Fast speed choice, a turns choice set to 100, and a Pedal mode switch with an RPM slider at 0.
InteractiveBike Generator Lab

Diego

I ride my bike. While it moved the meter read +6.0 mA, and once it stopped inside the coil it read 0 mA.
The Bike Generator Lab with the magnet sitting inside the coil and the meter at 0 mA. The run log reads 'Push in, Medium, 100 turns: peak +6.0 mA' and then 'Magnet sitting still inside the coil: 0 mA'.
InteractiveDiego's first run

Sparky

Nice, a fellow cyclist! So the meter jumped to +6.0 mA while the magnet was moving, then dropped to 0 mA the moment it stopped.

Understanding check

Where do you think that current came from?

Diego

The magnet inside the coil makes the current. Magnets have energy, so when it's in the coil the wire gets some of it.

Sparky

Interesting idea! Check your run log: what did the meter read in the row where the magnet was sitting still inside the coil? How does that compare to the rows where the magnet was moving?

Diego

It says "Magnet sitting still inside the coil: 0 mA". The +6.0 was only on the Push in row. So the magnet being inside isn't enough, it has to be moving?

Sparky

You figured that out from your own data. So if the magnet has to be moving, what's actually changing as it moves through the coil?

Diego

The magnetic field inside the coil changes. It gets stronger when the magnet goes in and weaker when it comes out.

Sparky

Exactly! Now think about your bike: why does a bike light get brighter when you pedal faster? Test your idea in the simulator and tell me what you find.

Diego

On Fast the log says peak +12.0 mA. On Medium it was +6.0. So pedaling faster makes the field change faster and you get more current?

Sparky

Your data backs that up. Now for the main challenge: charge the phone.

Diego

I turned on Pedal mode with 100 turns and pedaled at 120 RPM. Peak 18.0 mA, still Not charging.

Sparky

Getting closer! Which settings in your run log made the needle move the furthest?

Diego

Fast went further than Medium. And I never changed the turns. At 400 turns and 120 RPM it says peak 72.0 mA, phone charging!
The Bike Generator Lab in Pedal mode with 400 turns at 120 RPM: a magnet spins on a wheel next to the coil, the meter swings to −28.8 mA, the compass needle above the coil has turned away from north, and the phone reads Charging 37%. The last run log row reads 'Pedal mode, 400 turns, 120 RPM: peak 72.0 mA — phone charging'.
InteractiveDiego charges the phone

Sparky

Yes! So what were the two changes that got the phone charging, and why did each one help?

Diego

Pedaling fast and using 400 turns instead of 100. Faster makes the field change faster. More turns means more wire for the field to go through, so more current.

Sparky

Great reasoning! Now look at the compass while current is flowing. What does it do, and what does that tell you?

Diego

The needle swings back and forth with the meter. When there's no current it points north. So the current in the coil makes its own magnetic field?

Sparky

Exactly right. Now put it all together: explain in 2 or 3 sentences how a bike generator charges a phone, using your own readings.

Found his own mistake in the run log, then charged the phone

What Flint did for Diego

  • The simulator in Sparky's first message logged Diego's 0 mA reading, so the evidence against his idea was already on his screen.
  • Sparky asked a check question, then sent Diego to that row of his run log instead of telling him he was wrong.
  • After his right answer, Sparky asked the harder bike light question and had him test it in the simulator.
  • When Diego got stuck at 18 mA, Sparky asked which settings moved the needle furthest instead of naming the 400 turns.
  • Sparky graded his chat against the activity's rubric, which counts a mistake he fixed on his own toward Proficient.

A teacher can't stand next to 30 lab stations at the moment each student reads 0 mA and ask the right question. Sparky does it in every student's chat.

The activity page shows who thought a still magnet makes current

Activity analytics sums up what the class did across every chat. In this activity, Sparky's analysis guidelines ask it to note which students said a still magnet makes current and whether they fixed it on their own. If a student stays stuck, Sparky adds an alert under Needs attention while the class is still working.

Flint's activity page for an activity called Charge a Phone With a Bike: Build a Generator. Needs attention shows a live alert that one student wrote 'the meter must be broken, the magnet is still in there' after two questions about the 0 mA reading. Activity analytics lists what the class does well, including 13 students who fixed the still-magnet idea after checking their run log, an area of improvement where 16 students first said the magnet inside the coil makes the current, and a follow-up with a button to create a follow-up activity. The Sessions table shows two submitted students graded Proficient and Developing and one still in progress.

Example activity page

After a physics class finishes the bike generator lab

The school and students are made up for this page. In this example, 16 students first said a still magnet makes current, and most of them changed their answer after reading their own run log.

Set up the activity for free

The bike generator activity is in Flint's public library, with the simulator, Sparky's guidelines, the greeting and a rubric already set up. Open it, select Use activity to copy it into a free Flint account, and move it to a class. In the activity's Preview tab, select Try session myself to run the lab as a student before you assign it.

For more science activities, see Flint for science.

Start the activity for free

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