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Physics/Portable Electric Hot plate for Cooking.


Dear Prof Steve

Is it possible to design a portable electric Hot Plate for cooking which is battery operated?.


Hello Prashant,

Yes, of course it is possible.

The obvious next question is "would it be practical?"
Assume you need to boil 4 liters of water that is initially at 20 degrees C.

Calculate how much heat is required to raise the temperature of the water to 100 degrees C.
deltaQ = m*c*deltaT
So we need:
the mass, m, of 4 liters of water = (1 kg/liter)*4 liters = 4 kg
heat capacity/m, c, for water = 4.186 kJ/( C)
deltaT = 80 degrees C
So deltaQ = m*c*deltaT = 4 kg*4.186 kJ/( C)*80 degrees C = 1340 kJ

Calculate how much heat is needed to change that water to steam.
Q = m*L
So we need:
the heat of fusion, L, of water = 334*10^3 J/kg
So Q = m*L = 4 kg*334*10^3 J/kg = 1336*10^3 J = 1336 kJ

Total heat energy required is 1340+1336 = 2676 kJ = 2.68 MJ

The following website includes a table of energy density in various energy sources
It gives the energy density of a non-rechargeable lithium battery as 4.32 MJ/liter. That appeared to be the highest energy density among the batteries. So that says that the (non-rechargeable) lithium battery barely able to handle the above task would be about 0.62 liters in size. This assumes that no heat is lost to the surroundings. That of course would not be achievable.

I leave it up to you to decide if this would be practical.


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Steve Johnson


I would be delighted to help with questions up through the first year of college Physics. Particularly Electricity, Electronics and Newtonian Mechanics (motion, acceleration etc.). I decline questions on relativity and Atomic Physics. I also could discuss the Space Shuttle and space flight in general.


I have a BS in Physics and an MS in Electrical Engineering. I am retired now. My professional career was in Electrical Engineering with considerable time spent working with accelerometers, gyroscopes and flight dynamics (Physics related topics) while working on the Space Shuttle. I gave formal classroom lessons to technical co-workers periodically over a several year period.

BS Physics, North Dakota State University
MS Electrical Engineering, North Dakota State University

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