i think it is based on heating effects of electric current

Question

A heater at 220 V boils a volume of water in 5 minute time. If the heater is operated at 110V, the
same volume of water will boil in 10n minute. Find the value of n ?

Answer 1

The electrical power is what determines the rate of heating, not just the voltage.  The power is the product of voltage and current.  I will assume that the current is the same in both situations, since no other information is given.  Then the voltage and heating time should be inversely proportional.

 

(220 V)(5 min) = (110 V)(10n min)

 

n = (220)(5) / [110(10)] = 1

 

Note the answer makes sense.  If you have only half as much voltage (at the same current), you have half as much power, so it should take twice as long to heat, i.e. 10 min instead of 5 min (n = 1).