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I agree that a connection between the P=U*I formula and the
general definition of power should be made. Therefore the
following paragaraph (devoted to this well known topic)
will be added at the end of my essay.
15) Power is the rate at which energy is converted from one
form to another; the unit of power, watt, is joule per second. Is
the P=U*I formula consistent with this definition? The answer
is "yes" because volts are joules per coulomb (V=J/C) and amperes
are coulombs per second (A=C/s). Clearly, the product of U and I
shows how much energy (joules) is either gained or lost by circulating
charges in one second. This can be verified by algebraic manipulation
of units: 1V*1A=1J/C*1C/s=1J/s=1W. Circulating charges gain
energy inside the battery and loose energy outside the battery. This is
the central idea of an electric circuit. Lost energy increases the
temperature of wires and may appear in the form of light (from a lamp),
in the form mechanical energy (in a motor), etc. The circuit element in
which charges gain energy is usually referred to as an electric source or
an electric generator. Chemical batteries are examples of a generators.
Ludwik Kowalski
********************************************************
Kossom wrote:
Howdy-
From: Ludwik Kowalski [mailto:kowalskiL@MAIL.MONTCLAIR.EDU] Sent: Tuesday,
July 31, 2001 2:23 PM
The first formula which came to my mind was P=F*v. But is
it really a good analogy for the P=U*I ? Probably not. What
would be a better analogy, at the level of my description?
Why not continue the physical analogy?
Gravitational potential energy = mass x strength of gravity x the vertical
displacement. The amount of charge (or water) moved is simply the mass. The
other two terms are wrapped up together in the single term of voltage. It is
easy to imagine how voltage can combine how hard it is to raise water in a
place and how far the water was raised. So, the energy of a circuit would be
how many charged were moved x how hard it was to move them.
The power in the electrical circuit is the same as it is in the mechanical
circuit. It is the energy divided by the time. E /t = (q / t)x V, and q / t
= I. So, P = I V.
QED. Wait, qEd=U. Hey, that's what I've been saying.
Marc Kossover
mkossover@newman.k12.la.us
"Teaching is five shows a day" -- Dema Harriman Solberg