The Faraday’s Law simulation from PhET lets you move a magnet through a coil and see how a changing magnetic flux produces a voltage and lights a bulb. You can change the speed of the magnet, the side it enters from and the size of the coil, and watch the voltage change in size and sign. It is free, runs in any browser on a phone, tablet or laptop, and it is a great fit for the electromagnetic induction lessons in Tamil Nadu State Board (Samacheer Kalvi) Physics.
What is the Faraday’s Law simulation?
This interactive simulation lets you investigate how a changing magnetic flux can produce electricity. You can move a magnet through a coil and see the bulb light up and the voltage change. Because it runs on HTML5, there is nothing to install, and it works on phones, tablets, Chromebooks and computers.
Middle school to university
Induction, magnets, flux and voltage
Phone, tablet, Chromebook, PC
English
PhET’s learning goals are to explain what happens when a magnet moves through a coil at different speeds, and how this changes the brightness of the bulb and the size and sign of the voltage, to explain the difference between moving the magnet in from the right and from the left, and to explain the difference between a big coil and a smaller one.
Launch the Faraday’s Law simulation online
Tap or click inside the player and start exploring. Use the full-screen button in the player for a bigger view.
Credit: University of Colorado Boulder
How to use the Faraday’s Law simulation, step by step
- Predict first. Before you move the magnet, say whether you expect the bulb to light up.
- Move the magnet slowly. Push the magnet through the coil and watch the bulb and the voltage.
- Move it faster. Repeat at a higher speed and compare the brightness and the voltage.
- Change the side. Move the magnet in from the other side and watch what happens to the sign of the voltage.
- Change the coil. Try a bigger coil and a smaller coil and compare the results.
Tip for students: keep the magnet still for a moment and watch the bulb. A magnet that is not moving does not make a voltage.
The idea behind the simulation: ε = −N × ΔΦ ÷ Δt
ε = − N × ΔΦ ÷ Δt
Here ε (epsilon) is the induced voltage (emf) in volts, N is the number of loops in the coil, ΔΦ is the change in magnetic flux in webers (Wb) and Δt is the time the change takes in seconds. A faster change, or more loops, gives a bigger voltage. The minus sign is Lenz’s law: the induced current opposes the change that caused it. The calculator below shows the size of the voltage.
Worked example: A coil has 50 loops. The flux through it changes by 0.004 Wb in 0.2 s. The size of the induced voltage is 50 × 0.004 ÷ 0.2 = 1 V. If the same change happens twice as fast, in 0.1 s, the voltage doubles to 2 V.
Electromagnetic induction key terms explained
These are the words you will meet while using the Faraday’s Law simulation, with simple meanings.
Electromagnetic induction
Making a voltage in a coil by changing the magnetic field through it.
Magnetic flux (Φ)
A measure of how much magnetic field passes through a coil, in webers (Wb).
Induced emf
The voltage made in the coil by a changing flux.
Coil (loops)
A wire wound into many turns. More loops give a bigger voltage.
Magnet
An object with a magnetic field around it. It has a north and a south pole.
Faraday’s law
The induced voltage equals the rate of change of magnetic flux through the coil, times the number of loops.
Lenz’s law
The induced current flows in the direction that opposes the change that made it.
Voltage
The push that makes current flow, measured in volts (V).
Common mistakes: Thinking that a magnet sitting still inside a coil makes a voltage, forgetting that the voltage depends on how fast the flux changes, and ignoring that reversing the motion reverses the sign of the voltage.
Try the induced voltage calculator (practice what you explore)
Enter the number of loops, the change in flux and the time it takes. The calculator gives the size of the induced voltage. Then tap a “what if” button.
What happens when you change a variable
| Change | Effect on the voltage |
|---|---|
| Move the magnet faster | Bigger voltage, brighter bulb |
| Keep the magnet still | No voltage |
| More loops in the coil | Bigger voltage |
| Reverse the direction of motion | The sign of the voltage reverses |
| Stronger magnet | Bigger flux change, bigger voltage |
Classroom activities for teachers
The Faraday’s Law simulation fits a single 40-minute period.
- Predict and test (10 min): students predict how the bulb responds to each change, then check.
- Speed test (10 min): students move the magnet at slow, medium and fast speeds and record the voltage.
- Big coil, small coil (10 min): students compare the two coils and explain the difference.
- Exit ticket (10 min): students explain in two sentences why a magnet that is not moving does not light the bulb.
Looking for the matching chapters? Browse the Science and Physics books on TN SchoolBooks and download the Samacheer Kalvi PDFs, then use this simulation to make the electromagnetism lessons visual. More free science simulations and textbook PDFs are on the home page.
Quick quiz: test your understanding of induction
Score: 0 / 5
Faraday’s Law simulation: frequently asked questions
Is the Faraday’s Law simulation free?
Yes. PhET simulations are free to run online in a browser. Check PhET’s licensing page for reuse terms.
Does it work on a mobile phone?
Yes. It is built with HTML5 and works on phones, tablets and Chromebooks. Use landscape mode or the player’s full-screen button for a bigger view.
What does Faraday’s law say?
Faraday’s law says that a changing magnetic flux through a coil induces a voltage in it. The size of the voltage equals the number of loops times the rate of change of flux.
Why does a still magnet not light the bulb?
A voltage is made only when the magnetic flux through the coil is changing. A magnet that is not moving gives a steady flux, so there is no induced voltage.
The Faraday’s Law simulation turns an invisible effect into something you can move, measure and see. Explore it, take the quiz above, and keep experimenting until predicting the voltage feels easy.