How Long Will It Take to Heat Water in an Electric Kettle?

[chawki]

Homework Statement

In an electric kettle with good heat insulation 0.85 kg water is warmed by an electrical resistance of 25 Ohms, which is connected to a voltage of 230 V. The specific heat capacity of water is 4190 J/(kg°C)

Homework Equations

In what time will the temperature of the water rise by 20 °C?

The Attempt at a Solution

P=E/t
but here we can calculate only Q
are they the same?

 

[gneill]

Compare the units. One is a rate, the other is an amount.

 

[chawki]

Please check this thread https://www.physicsforums.com/showthread.php?t=478370
it's nearly typical
and regarding the units..they are same i think..Joule...Joule

 

[gneill]

Power is Joules/second. Heat is Joules. One is a rate, the other an amount.

 

[chawki]

Yes, i was meaning Q and E
i was meaning if we can write P=Q/t anstead of P=E/t...because both Q and E are energies and joules.

This is how i solved it..
Q=m*Cp*delta T
Q=0.85*4190*20
Q=71230 J

then we calculate P
P=V²/R
P=230²/25
P=2116 watt

P=Q/t
t=Q/P
t=71230/2116
t=33.66 seconds ?

 

[gneill]

Forms of energy are interconvertible under the appropriate circumstances. Certainly electrically produced heat energy can be used to add heat to physical substances.

 

[chawki]

Is my answer and the way i have written it correct ?

 

[gneill]

Is my answer and the way i have written it correct ?

Sure. Well done. Although if you have time, you should annotate the calculations a bit to explain what it is you're calculating in each section. It's a bit like writing good computer code... imagine that someone who has never seen it before needs to understand it in a hurry.

 

[chawki]

Thank you gneill