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Electromagnetic Induction - A Shaking Flashlight

An electromagnetic flashlight with transparent barrel lets you see how a moving magnet within a coil of wire will induce a current.

The moving magnetic field line (flux pattern) cuts through the wires causing electromagnetic induction. If you look inside the clear case as you shake, you will see the powerful magnet pass back and forth through a loop of wire.

In the scientific demo model pictured on the right:

The electrical energy produced is stored in a capacitor that can be charged hundreds of thousands of times.

The bulb is an energy efficient ultra-bright white LED.

30 seconds of shaking provides a full charge, and will produce a beam  of light for several minutes.

You set the switch to charge and shake the flashlight to charge up the capacitor.

Then you flip the switch to let the energy stored in the capacitor light the LED.

For this to work practically you need a powerful permanent magnet - such as one made of neodymium. One of these magnets will be small but have a very dense array of flux lines (strong magnetic field) around it.

The permanent magnet is inside a plastic track which allows it to slide up and down. When you shake the flashlight, the permanent magnet passes through the copper coil repeatedly.

 

The problem with this type of magnet is that the flashlight will have a strong magnetic field - and may well interfere with analogue watches or cards with magnetic strips of info on them!

You therefore should not store such a flashlight in your handbag near your credit cards!

Manufacturers have made flashlight torches like this that use the electrical energy produced to charge up a rechargable battery. In that way a bit of protracted shaking can store enough energy to produce a longer 'light up' time. If you search on the web you will find lots of offers of these flashlight torches for sale.

Want to make your own?

Here is an E-How link that tells you how to do it!