We need help with specific heat capacity and
U values. Please have pity on us!
Specific heat capacity is a little bit like your
answer to the density question. Just as density is mass over volume
then the 'density' of heat that something can hold is heat over
mass. Specific heat is the amount of heat required to raise the
temperature of so much of something by a certain amount. It is usually
the amount of heat required to raise 1kg of something by one degree.
The key to understanding this is to realise the difference between
amount of heat (which is energy) and temperature. And the best way
to understand this is to think about bath time and a red-hot poker.
A red-hot-poker might be very hot (glowing even) but a large hot
steaming bath will contain more heat energy than the poker when
compared to a cold poker and a cold bath. Even though the poker
is much hotter than the bath it actually took less energy to get
the poker red-hot than it did to heat-up all that bath water(because
there's more of it). So that is the difference between heat and
temperature but what links them together? Answer - specific heat.
How do you get a kilogram of water from 20 degrees to (lets say)
30 degrees? the answer is you have to heat it up (i.e. put heat
in) How much heat will it take? The specific Heat Capacity of water
is 4,200 Joules per Kilogram per Kelvin which means that if you
have one kilo of water and you want it to be hotter by one degree
it will take 4,200 joules of heat to do it. We want it to go from
20C to 30C and so it will take ten times as much heat i.e. 42,000
joules or 42kJ. Most of the questions on this subject relate to
the fact that different things take different amounts of heat to
warm them up so, if you are putting heat into two things at the
same rate - some will get hotter quicker than others. I hope that
I've explained this simply but - if I have only made it more complicated
let me know.
Brian
Just how big is the Elephant ?
HomeWork Elephant is receiving over
100,000
page
impressions per month (and growing).
Check-out
the 
