1   kg of water, at 20   ° C is heated in an electric kettle whose heating element has a mean…

1 kg of water, at 20 °C is heated in an electric kettle whose heating element has a mean (temperature averaged) resistance of 20 Ω. The rms voltage in the mains is 200 V. Ignoring heat loss from the kettle, time taken for water to evaporate fully is close to
[ Specific heat of water =4200 J kg-1 °C-1 Latent heat of water =2260 kJ kg-1 ]
  1. 3 min
  2. 16 min
  3. 22 min
  4. 10 min

Solution

Given specific heat of the water 4200 J kg-1 °C-1

Latent heat of the water =2260  kJ kg-1  

Q=P×t

Q=mcΔT+mL

⇒P×t=mcΔT+mL

⇒Vrms2R×t=mcΔT+mL

⇒200220×t=4200×80+2260×103

⇒t=1298 s≃22 min

Asked in: JEE Main 2019 (12 Apr Shift 2)

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