When the room temperature is 25^ C , an electric kettle used for preparing tea takes 2 minutes to boil 4 cups of water (where 1 cup contains 200 cc of water). Calculate the cost of boiling 4 cups of water, given that the cost of power consumption is Re 1.00 per unit ( 1 unit = 1000 watt-hour).

Step-by-step solution

Mass of water, m = 4 200 cc 1 g/cc = 800 g = 0.8 kg Specific heat capacity of water, s = 4200 J kg ⁻¹ ^ C ⁻¹ Change in temperature, T = 100^ C - 25^ C = 75^ C Heat required to boil the water, Q = m s T Q = 0.8 4200 75 = 252000 J Since 1 unit = 1 kWh = 3.6 10^6 J , the electrical energy consumed in units is: Number of units = 252000 3.6 10^6 = 0.07 units Given the cost of power is Re 1.00 ( 100 paise ) per unit, the total cost is: Cost = 0.07 100 paise = 7 paise