# EMF in an Open Circuit?

Lets assume we have a wire passing a magnetic field, it is know that EMF is induced due to the magnetic field, what if the wire is not connected to a circuit what happens?

Is there ay voltage in the wire? I doubt there, is.. and current can not flow in an open circuit so what will happen?

A loop of wire, with the ends not touching nor connected to anything else, is this:

simulate this circuit – Schematic created using CircuitLab

If you look at the schematic, it even makes intuitive sense, graphically. As you can see at the gap between the capacitor "plates", the "wires" are not touching. That the plates (which are really just the wires that make up your loop) are really small and far apart doesn't make it not a capacitor: it just makes the capacitance very low, some picofarads at most.

Normally it's so low we can ignore it, but in this case, there's nothing else, so it's pretty key. When the magnetic flux through the loop changes, an EMF is induced just as you'd expect. Some current does flow, according to the governing laws of a capacitor:

$$I(t) = C\frac{\mathrm{d}V(t)}{\mathrm{d}t}$$

Of course, with C = 1pF, the current will be very low indeed, and if the EMF isn't changing ($\mathrm{d}V(t)/\mathrm{d}t = 0$), then there is no current.

• EMF would be the same value regardless of the circuit being open or closed correct? Apr 3, 2014 at 5:33