1.

An immersion heater, in an insulated vessel of negligible heat capacity brings 10 g of water to the boiling point from `16^@C` in 7 min. Then Q. Power of heat is nearlyA. `8.4xx10^3`B. 84 WC. `8.4xx10^3(cal)/(s)`D. 20 W

Answer» Correct Answer - B
In 7 min, temperature of 100 g of water is raised by
`(1000-16^@C)=84^@C`. The amount of the heat provided by heater
`Q_W=C_Wm_WDeltaT=((1cal)/(g^@C))(100g)(84^@C)`
`=8.4xx10^3cal=(8.4xx10^3xx4.186)J`
`=3.5xx10^4J`
Power of heater `=(Q_W)/(t_1)`
`=(8.4xx10^3cal)/((7xx60)s)=20(cal)/(s)`
`=(20xx4.18)(J)/(s)=83.6Wapprox84W`


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