Question

The EMF of a cell can be defined as:
(A) Work done in taking a unit positive charge once round the circuit.
(B) The open circuit voltage of the cell
(C) The terminal voltage when the current is zero
(D) All the above

Answer 1

The EMF can be defined as the sum of the potential difference produced by charges which are separated and that can occur at each phase boundary inside the cell. The magnitude of the potential difference depends upon the chemical nature of the two contacting phases. The potential difference causes the charge to move from one end of the cell to the other. Potential difference is measured in Volts.

Complete answer:
EMF is defined as the Electromotive force of a cell. All the cells have their own potential difference when they have not been used yet. The original potential difference of the cell is the EMF and we can say in other terms as the potential difference across the terminals of a cell when no current is drawn from it. So, option C is correct.

Also, it can be defined as the work done in moving a unit positive charge once round the circuit. So, option A is also correct.When no current is drawn from the cell, the potential across its terminals is called the EMF. So, option B is also correct. Since A, B and C are all correct thus all the options mentioned are correct and the answer is D.

Hence, the correct answer is option D.

Note: Electric potential is a scalar quantity and it is assumed to be zero at the infinity. If we want to move a charge from one point to another and if the electric potential is same at both the points work done will be zero because no work is required to be done to move a charge on an equipotential surface.The electric potential is related to electric field and electric field is defined as the negative gradient of electric potential.