First a set of n equal resistors of R each are connected in series to a battery of emf E and internal resistance R. A current I is observed to flow. Then the n resistors are connected in parallel to the same battery. It is observed that the current is increased 10 times. What is ‘n’?
In the first case, n resistors are connected in series with a battery of emf E and internal resistance R.
Equivalent resistance = (n+1) R
(1)
In the second case, n resistors are connected in parallel to the same battery.
Hence, equivalent resistance = 
(2)
From 1 and 2,
Hence, n = 10.
1