

Heat Calculations
Name: Jason
Status: other
Age: 20s
Location: N/A
Country: N/A
Date: 20002001
Question:
May I know how do I calculate the amount of heat generated
given the amount of current(I) passing through a length(L)of copper wire
of a certain width(W)?
Replies:
Power is energy/unit time and energy is the equivalent of heat.
The power of and electrical resistor is current x voltage or current x
current x resistance.
The electrical resistance is resistivity x length of wire/cross sectional
area.
I don't have the resistivity of copper at my finger tips, but it is
available through various hand books.
Hence the Heat=Power x Unit Time= (Current x Current x resistivity x length
of wire)/cross sectional area.
Dr. Myron
Assuming the material you are dealing with is ohmic, you find the
resistance by:
R = rho L/A
R is the resistance.
rho is the constant of resistivity associated with the material, and is
available in standard tables.
L is the length.
A is the cross sectional area.
Q = I^2 Rt
Q is for the energy exchange from electrical potential energy into thermal
energy.
I is the current.
R is the resistance.
t is for the amount of time the current is flowing.
This information is available in any standard introductory college text
containing electricity.
Nathan A. Unterman
Heat generated per unit time (i.e., power, as in Watts per second) is
given by P=V I=R I^2 where V is the voltage across the wire, R is the wire
resistance, and I is the current. Note that current and voltage are
related by V= R I.
The resistance of a copper wire of length L and crosssectional area A
(which must be known) is given by R= (r L)/A where r is the electrical
resistively of copper. Electrical resistively of metals are listed in text
books.
As you can see, you need two of the three items (R, I, V) to evaluate the
power. If you know V and I, you do not need to calculate R (use P=V I). If
only V or I is known, then evaluate R as in paragraph 2.
AK
Dr. Ali Khounsary
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Update: June 2012

