A) 2.03 V
B) 2.54 V
C) 1:25 V
D) 1.39 V
Correct Answer: D
Solution :
The emf of a cell is denned as work done by the cell in moving unit positive charge in the whole circuit including the cell once. Therefore, if W is the work done by a cell in moving charge q once around a circuit including the cell, then \[emf\,E=\frac{W}{q}\] or \[E=\frac{W}{it}\] Given, \[i=2A,\,t=6\,\min =6\times 60s,\,W=1000\,J\] Hence, \[E=\frac{1000}{2\times 6\times 60}=1.39\,V\] Note: The term emf (electromotive force) is misleading introduced by volta who thought it to be force that causes the current to flow. Actually emf is not a force but work required to carry unit charge from lower potential to higher potential inside the cell.
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