Ten identical cells each of potential E and internal resistance r are connected in series to form a closed circuit. An ideal voltmeter connected across three cells, will read

Step-by-step solution

Given: Initial number of cells (n₁ )=10 ; Potential of each cell =E ; Internal resistance of each cell =r and final number of cells (n₂ )=3 . We know from the Ohm's law, total voltage of ten cells =10 E=10 E and total resistance in ten cells =10 r=10 r . Therefore current in the circuit, I= 10 E 10 r = E r or potential difference across three cells =I 3 r= E r 3 r=3 E . (Since the voltmeter is ideal, therefore it will read 3 E) .