EMF & Terminal Difference: Batteries are such devices create a potential difference and can supply current if connected to a resistance. On the small scale, the potential difference creates an electric field that exerts force on charges, causing current. We thus use the name electromotive force, abbreviated emf. Emf is not a force at all; it is a special type of potential difference. To be precise, the electromotive force (emf) is the potential difference of a source when no current is flowing. Units of emf are volts. Electromotive force is directly related to the source of potential difference, such as the particular combination of chemicals in a battery. However, emf differs from the voltage output of the device when current flows. The voltage across the terminals of a battery, is less than the emf when the battery supplies current, and it declines further as the battery is depleted or loaded down. However, if the device’s output voltage can be measured without drawing current, then output voltage will equal emf (even for a very depleted battery). The voltage output of a device is measured across its terminals and, thus, is called its terminal voltage V. Terminal voltage is given by V=emf−Ir where r is the internal resistance and I is the current flowing at the time of the measurement.
Posted on: Fri, 27 Sep 2013 19:06:06 +0000