A kettle with 2 litre water at `27^@C` is heated by operating coil heater of power 1 kW. The heat is lost to the atmosphere at constant rate `160 J//s`, when its lid is open. In how much time will water heated to `77^@C` with the lid open ? (specific heat of water = `4.2 kJ//^@C-kg)`A. 8 min 20 sB. 6 min 2 sC. 14 minD. 7 min

A kettle with 2 litre water at `27^@C` is heated by operating coil hea

1.	A kettle with 2 litre water at `27^@C` is heated by operating coil heater of power 1 kW. The heat is lost to the atmosphere at constant rate `160 J//s`, when its lid is open. In how much time will water heated to `77^@C` with the lid open ? (specific heat of water = `4.2 kJ//^@C-kg)`A. 8 min 20 sB. 6 min 2 sC. 14 minD. 7 min
Answer» Correct Answer - A Net power available per second, `P = 1000 - 160 = 840 J//s` Heat required, `Q = msDeltatheta = (2)(4200)(77-27)` `=420000 J` `:. `Time required `= Q/P = 500 s = 8 min 20s`.

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