UCSB Science Line
Sponge Spicules Nerve Cells Galaxy Abalone Shell Nickel Succinate X-ray Lens Lupine
UCSB Science Line
How it Works
Ask a Question
Search Topics
Our Scientists
Science Links
Contact Information
How long does it take for water to boil?
Question Date: 2012-10-03
Answer 1:

This is a breadbox physics/engineering question.

The process is a fairly simple one:

A container with some amount of water (lets say 1 kg for simplicity) is heated using some source (let's say an electric heating element that outputs Q (energy)= 2,500 Watts or Joules/second)(Joules is an energy unit).

All we need now is the starting temperature of the water (we'll say 25 Centigrade) and the heat capacity (4186 Joules/kg*Kelvin)(Kelvin is a unit of temperature degrees).

So, how much heat do we need to add to 1kg of water in order to heat it from T0=25 Centigrades to T1=100 Centigrade?

Well, this is precisely what heat capacity means, it's been measured, and it is ~4186 Joules/kg Kelvin.

Q_Required = (100 - 25) Kelvin * 4186 Joules/ (kg Kelvin) * 1kg = 314,000 Joules

We said earlier that our stove supplies ~ 2,500 Joules/second, so 314,000 Joules / (2,500 Joules/second) = 126 seconds.

Time it! Remember 1 kg is about 1 Liter of water. Our estimate is likely low (based on personal experience) and is likely due to an over estimate of the heat output of the stove (not 100% of the stove's heat goes directly to the water; much of it is wasted in hot air escaping around the sides of the kettle).

Click Here to return to the search form.

University of California, Santa Barbara Materials Research Laboratory National Science Foundation
This program is co-sponsored by the National Science Foundation and UCSB School-University Partnerships
Copyright © 2020 The Regents of the University of California,
All Rights Reserved.
UCSB Terms of Use