The terminal voltages of a cell are found to be 29 V and 28 V when it delivers currents of 1 A and 2 A, respectively. The emf and the internal resistance of the cell are, respectively
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → \( 30\,\mathrm{V} \); \( 1\,\Omega \)
When a cell delivers a current \( I \), its terminal voltage is less than the emf by the drop across the internal resistance:
\( \displaystyle V = E - Ir \)
Writing this for the two readings:
\( 29 = E - (1)\,r \)
\( 28 = E - (2)\,r \)
Subtracting the second from the first:
\( \displaystyle 1 = r \;\Rightarrow\; r = 1\,\Omega \)
\( \displaystyle E = 29 + 1 \times 1 = 30\,\mathrm{V} \)