I take a 12 volt battery, take a strong electromagnet, and fire it up.

I then touch the two terminals that are currently connected, one terminal of the battery, and one terminal of the electromagnet.

When I disconnect the terminal of the electromagnet to one terminal of the battery, while still placing my thumb over the terminal of the electromagnet and the battery, I receive a little shock.

I know that the inductor releases a higher voltage when disconnected, but why?

•The magnetic field is induced with an inductor with X amount of turns when the battery is connected.

• The battery is now released, and the magnetic field closes down, and induces a current on the inductor with X amount of turns.

Heres where I am confused- both X's are the same amount of turns, therefore a 1 to 1 ratio. Why are different voltages present with the same voltage source, a 12 volt battery?


Changing currents in an inductor result in changes of magnetic flux in the inductor. Then, since the flux changed, the induced voltage changes. That is why

\$v = L{di \over dt} \$

Thus, when you disconnect the inductor, the current changes from whatever it was to 0 in a very short amount of time. The resulting \${di \over dt} \$ becomes very large making the induced voltage very large.

  • \$\begingroup\$ The formula has a - in front of it to indicate that it's in the opposite direction.It is a minor matter however. \$\endgroup\$ – Daniel Tork Aug 14 '16 at 4:36

When you disconnect the battery, the magnetic field of inductor will collapse. This collapsing magnetic field will produce current. However since the circuit is open, the moving electrons (current) has no where to go but to accumulate on the open end of the circuit, therefore producing high voltage. Thats the little shock you sensed.

  • 1
    \$\begingroup\$ The electrons don't accumulate - unless you think there is some capacitance. Read Justin's answer. You will find that your posts will be taken much more seriously if you use proper capitalisation as it improves readability and gives a much more favourable impression of the author. \$\endgroup\$ – Transistor Aug 13 '16 at 22:35
  • \$\begingroup\$ It is sometimes convenient to think of inductors giving electrons innertia. it removes the need to consider the magnetic field. and in the real world there is always some capacitance involved. \$\endgroup\$ – Jasen Aug 14 '16 at 1:06

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.