Question

An electric kettle is rated 5 kW. How much time will it take to boil 15 kg of water initially 15°C. if it is connected to 230 V supply? Of One unit of electric energy costs ? 1.21, find the cost incurred

Answer 1

Answer:

as per the steady flow energy equation....

if we consider the given factors then we get

dQ/dt=dW/dt

where Q denotes the amount of heat

t denotes time

W denotes the work required

we have given dW/dt=5 kW

then dQ/dt= 5*103

but Q= mCvdT

where m= mass= 15kg

Cv= specific heat at constant volume=4.186KJ/kgK

dT= change in temperature=100-15=850C

but in kelvin scale dT= 273+85= 358K

now puting all values

5= 15*4.186*358/dt

dt=4495.764 sec

power= work /time

5000J of work= 1 sec

4495.764sec =5000*4495.764 joule of work

so total work = 22478820 joule

i unit = 3600000 joule work

then units in 22478820 joule work =22478820/3600000

total units = 6.24 units

so total electricity cost = 6.24*1.21=Rs 7.5