Two coils require 20 minutes and 60 minutes respectively to produce same amount of heat energy when connected separately to the same source. If they are connected in parallel arrangement to the same source; the time required to produce same amount of heat by the combination of coils, will be _____ min .

Step-by-step solution

If H is the heat required to heat the water, then P 1 × 60 = H ⇒ P 1 = H 60 and P 2 × 20 = H ⇒ P 2 = H 20 When the coils are connected in parallel their powers will get added. If the required time now is t , then P 1 + P 2 t = H ⇒ t = H H 60 + H 20 = 15   min