Alexander Fufaev

Formula: Induced Voltage due to Magnetic Field Change

Bar Magnet Induces Current in a Metal Ring Hover the image!

Induced voltage

This electric voltage is formed, for example, between the end points of a wire loop when the magnetic field \( B \) penetrating the wire loop is changed. Notice: Only as long as the temporal change of the magnetic field happens, the induction voltage is measurable. As soon as the magnetic field is NOT changed (\( B \) constant), the voltage at the endpoints of the conductor loop disappears.

If the conductor loop is short-circuited, i.e. the two contacts are connected, then an induction current \( I_{\text{ind}} \) is generated in the conductor loop.

The minus sign in the induction law is justified by the Lenz rule in order not to violate the conservation of energy.

Magnetic field change

Magnetic flux density \( B \) enclosed by the conductor loop, which is changed by the value \( \Delta B \). If this flux density \( B \) changes in time, i.e. \( \Delta B \neq 0 \), then an induced voltage or induced current is generated in the conductor loop.

Time span

This is a time span within which the magnetic flux density has changed by the value \( \Delta B \). The smaller the time span within which the magnetic field has changed, the greater the induced voltage.


Area enclosed by the conductor loop. According to this formula, \( A \) is not changed, i.e. in this case it is assumed that the area remains constant. This means: the conductor loop is not bent or manipulated in any other way to change the area penetrated by the magnetic field.