- Physics
- Ready-made model
- Class 10 to 12
Ontex Electronics Self Induction of an Inductor Using Coil Physics Investigatory Project Model Engineering College & Science Teaching Aid
Code B0DMKZD5L7
- Paid for and delivered by Amazon. The current price and the delivery date for your PIN code are shown there.
- Sold by Gurukul Technicals Institute, Delhi.
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In this project guide
Ready-made model
About this model
This investigatory project model demonstrates self induction: the way a coil opposes any change in the current flowing through it. It helps a student see an effect that is usually explained only with equations, which makes the chapter on electromagnetic induction easier to present and defend in a viva. It suits Class 12 physics projects and engineering first-year teaching.
How it works
The science behind it
The idea the model demonstrates, in words you can use in your report and when you explain it.
When the current through a coil changes, the magnetic flux linked with the coil also changes, and by Faraday's law an emf is induced in the same coil. This is self induction. By Lenz's law the induced emf opposes the change that causes it, which is why it is often called back emf. Its size is e = −L (dI/dt), where L is the self inductance, measured in henry (H). For a long solenoid, L = μ0 μr N²A/l, so more turns, a larger cross-section or an iron core gives a larger inductance. If the current is switched off suddenly, dI/dt is very large, so a large emf can appear across the coil for a moment. The choke in an old tube light used exactly this: when the starter broke the circuit, the choke produced a high voltage spike that lit up the tube.
Make it yourself
Make a self-induction coil model yourself
Build your own version from scratch, or use the steps to understand how the ready-made model is put together before you present it.
What you need 9
Step by step 8 steps
Measure the coil's resistance with the multimeter and note it down.
Set up two branches across the cells: bulb A in series with the coil, and bulb B in series with the variable resistor, both controlled by the push button.
Hold the button down and adjust the variable resistor until both bulbs glow equally once the current is steady.
Release, wait a few seconds, then press again while watching closely: bulb B lights at once and bulb A lags a little behind, because the coil's back emf opposes the rising current. With a home-wound coil the lag lasts only a fraction of a second, so film it in slow motion on a phone if you cannot see it.
- Now build the second test
The coil, the 47 Ω resistor and the push button in series with the cells (a high-resistance relay coil does not need the resistor).
Connect the LED across the coil the reverse way, with its long leg to the end of the coil that goes towards the cells' negative.
- Press and hold the button
The LED stays dark. Release it: the LED flashes, powered only by the energy stored in the coil's magnetic field.
Take the iron out of the coil if you can and repeat both tests; the delay and the flash both become weaker.
Read this first
Safety first
Go through these points before you build or switch anything on. Younger students should do this with an adult.
- Use only cells or a battery up to 9 V; never connect the coil to mains or to a modified adapter.
- When a coil's current is switched off, a brief voltage much higher than the cells' can appear across it, so do not hold the coil ends while switching off.
- Keep the series resistor in place with a low-resistance coil, or the cells and the coil will heat up.
- Remove the cells when the model is not being shown.
Troubleshooting
If something does not work
The usual problems with this model and how to fix them. Open a problem to see the fix.
Both bulbs light at the same moment
The coil's inductance is too small to show the delay. Use more turns and a thicker iron core, and film the switching in slow motion on a phone to see the lag.
The LED glows all the time while the button is pressed
It is connected the wrong way round. Reverse it so it is reverse-biased while the current flows normally.
There is no flash when the button is released
The coil current is too small, or the cells are weak. Check the resistor value and fit fresh cells.
Bulb A never gets as bright as bulb B
The variable resistor is not balanced against the coil's resistance. Readjust it with the button held down until both match.
Exhibition day
How to present it
A running order for the exhibition table or the practical, step by step.
Explain the demonstration in the order: change in current, change in flux, induced emf, effect you can see.
Write e = −L dI/dt on the chart and explain what the minus sign means.
If the model uses an iron core, show the result with and without it to prove that inductance depends on the core.
Warn viewers not to touch the coil terminals when the switch is opened, since the back emf can give a small shock.
Practice
Viva questions
Practice questions on this model, with short answers. Try each one aloud before you open the answer.
What is self induction?
It is the production of an induced emf in a coil due to a change in the current through the same coil.
What is the SI unit of self inductance?
The henry (H). A coil has an inductance of 1 H if a current changing at 1 A/s induces an emf of 1 V in it.
Why is the induced emf called back emf?
Because, according to Lenz's law, it opposes the change in current that produces it.
How does an iron core change the inductance of a coil?
Iron has a high relative permeability, so it greatly increases the magnetic flux for the same current, and the inductance rises.
Project file
Project file outline
The headings of the project file, in order. Give each heading its own section and write it in your own words.
Free ebook: Writing a Science Project FileContents
- Aim: to demonstrate self-induction with a delayed bulb and a switch-off LED flash
- Back emf at switch-on and switch-off, explained with Lenz's law
- Self-inductance of a coil and the effect of an iron core
- Circuit diagrams of the two experiments
- Observations at switch-on and switch-off, with and without the core
- Energy stored in an inductor, U = ½ L I²
- Sparks at switches and why diodes are fitted across relay and motor coils
- Precautions against the switch-off voltage spike, and conclusion
Buying checklist
Before you buy
What to check before you order the model.
1Check these first
- Check the listing for the power source and whether the model uses bulbs, LEDs or a meter, so your file matches the real model.
- Confirm with your teacher that it fits the Class 12 chapter on electromagnetic induction.
- Test it at home before the exhibition and practise explaining the switch-off effect for your viva.
- Keep the box, and protect the coil's thin wire from scratches.
- Check the delivery date for your PIN code on the marketplace, and order well before the exhibition or practical.
Next steps
Take it further
Ways to turn this model into a bigger investigation or a stronger exhibition entry.
Film the switch-on delay in slow motion for coils with different numbers of turns and compare them.
Explain why a diode is fitted across relay coils in real circuits, using your LED test as a model of that diode.
Estimate the coil's inductance from its size and number of turns with the solenoid formula.
Audience
Who it suits
Class 12 physics investigatory projects on electromagnetic induction, and engineering first-year physics or electrical labs.
- ClassClass 10 to 12
- SubjectPhysics
- TypeReady-made model
Free to read
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