Electromotive Force (e.m.f) | Measurement Of Potential Difference | Measurement Of e.m.f

Electromotive Force

A wellspring of electromotive force (e.m.f) changes over non-electrical energy (compound, warm, mechanical, and so forth.) into electric energy. Examples of source of e.m.f are batteries, thermoplastic and generator. When a conductor is connected to a battery, current flow through it due to potential difference.

Electromotive Force

For the continuous flow of current through a wire, battery supplies energy to the chargers. The positive charge leaves the positive terminal of the battery, goes through the conductor and achieves the negative terminal of the battery. As a positive charge enters the battery at its lower potential point. (negative terminal), the battery must supply energy, say W to the positive charge to drive it to point of higher potential i.e, positive terminal. Now we define e.m.f. of the source as:

it is the energy supplied by a battery to a unit positive charge when it flows through the closed circuit. Or The energy converted from non-electrical forms to electrical forms to electrical form when one coulomb of positive charge passes through the battery.

Thus

The unite for e.m.f., W is J/C which is equal to volt (V) in SI system. Hence, if the e.m.f. of the battery is 2 V, the total energy supplied by the battery is 2 joules when one coulomb of charge flow through the closed circuit.

The Measurement Of Potential Difference 

    The potential difference across a circuit components ( e.g. light bulb) can be measured by a voltmeter associated straightforwardly over the terminal of the part. The positive terminal of the battery is connected to the positive terminal of the voltmeter and the negative terminal of the battery is connected to the negative terminal of  the voltmeter.

An ideal voltmeter should have very large value of the resistance so that no current passes through it. Voltmeter is always connected in parallel with the device across which the potential difference is to be measured.

The Measurement Of e.m.f 

  In general, e.m.f refers to the potential difference across the terminal of the battery when it is not driving current in the external circuit. So in order to measure e.m.f of the battery we connect voltmeter directly with the terminal of the battery as shown in Fig.