About James Joule
 |
| James Prescott Joule |
James Prescott Joule (1818–1889), Scotland.
James Prescott Joule was one of five children in the
family of a well-to-do brewery owner. Since he was a
sickly child with a spinal deformity, both he and his
brother were educated at home until the age of 15 and
later by private tutors.
The famous English chemist, John Dalton, taught
them chemistry, physics, and the methods of
scientific experimentation.
Later in life Joule acknowledged that John Dalton encouraged him to increase his knowledge of science and of original research.
When James’ father died, he and his brother ran the
brewery, which prevented him from attending a
university. However, this did not deter him from setting
up a laboratory in his home and continuing his interest
in science after his day at the brewery.
He became proficient in mathematics and learned how
to make accurate measurements in the
His home experiments resulted in his ability to
measure slight increases in temperature under
various conditions, which led to his theory for the
equivalence of work and heat energy.
The unit of work and energy was named after him (the Joule, or the symbol ‘‘J’’)
Now, with his law
Joule’S law
Joule’s law states that:
The relationship for heat produced by an electric current in a conductor is related to the resistance of the conductor times the square of the amount of current applied:
H = R I²
By experimentation, James Joule established the law
that states that when a current
of voltaicelectricity is sent through a metal or other type
of conductor, the heat given
off over a specifictime period is proportional to the resistance of
the conductor multi
plied by the square of theelectric current.
The equation for this law is: H = R I² , where H is
the rate of the heat given off as watts in joule units, R
is the resistance in the conductor in ohms and I² is
the amount of the current (amps) squared.
The application of Joule’s law
The application of this law is important in all
industries using electricity as a source of energy. The
resistance to an electric current flowing through a
conductor is analogous to the friction of air, the
movement of engine parts, and tires on the road
for a moving car. The electrical, as well as
mechanical, energy is not just ‘‘lost,’’ rather it is
converted to heat, just as is friction.
Joule was interested in improving the mechanical
advantage of electric motors, but because they were
very primitive during his lifetime, he devoted more of
his work to improving the efficiency of steam engines.
He accurately predicted that electric motors eventually
would replace most other types of mechanical devices.
Another law
:
Law for the mechanical equivalent of heat
: A fixed amount of mechanical work (expenditure of energy) ends up in a fixed quantity of heat.
An interesing story
Earlier in 1798 when Count Rumford was boring out
the brass barrels of cannons,
he noticed that large amounts of heat were generated.
It became obvious that friction
generated by the work of turning the bit in the metal
resulted in heat. Julius von Mayer
also was interested in this relationship and developed
a figure for the mechanical equivalent of heat that was
not very accurate.
James Prescott Joule was the first to consider heat
as a form of energy in his calculation.
He conducted exacting experiments to determine the
amount of heat generated not just by electricity but
also by mechanical work. Joule calculated the amount
of mechanical work needed to produce an equivalent
amount of heat.
He demonstrated that
41 million ergs of work
produced 1 calorie of heat, which is now known as
the mechanical equivalent of heat.
Since 10 million ergs are equal to 1 joule, named
after James Joule, 4.18 joules are then equal to 1
calorie of heat.
Joule’s work enabled others to perfect
the law for the conservation of energy, which states
that energy, like mass, cannot be created or destroyed
but can be changed from one form to another.
I hope that this post was useful.