A kettle with 2, littre water at 27,^oC is heated by operating coil heater of power 1, kW . heat is

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10-1.Thermometry, Thermal Expansion and Calorimetry

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A kettle with $2\, littre$ water at $27\,^oC$ is heated by operating coil heater of power $1\, kW$. The heat is lost to the atmosphere at constant rate $160\, J/sec$, when its lid is open. In how much time will water heated to $77\,^oC$. (specific heat of water $= 4.2\, kJ/kg$) with the lid open ?

A

$8\, min$ $20\, sec$

B

$6\, min$ $2\, sec$

C

$14\, min$

D

$7\, min$

Solution

(Power of heater)time $=$ (Rate of heat loss)time $+\mathrm{mS} \Delta \mathrm{T}$

$1000 t=160 t+(2)(4200)(50)$

$t=500 \mathrm{sec}$

Standard 11

Physics

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