UCSB Science Line
Sponge Spicules Nerve Cells Galaxy Abalone Shell Nickel Succinate X-ray Lens Lupine
UCSB Science Line
Home
How it Works
Ask a Question
Search Topics
Webcasts
Our Scientists
Science Links
Contact Information
In a circuit, if current is increased, heat will increase (heat is directly proportional to square of current) but if current increases ,resistance will decrease (resistance is inversely proportional to current) but if resistance decreases heat will decrease (heat is directly proportional to resistance)tell me whether heat is increased or decreased?
Question Date: 2018-06-13
Answer 1:

Heat given off by a circuit is a form of energy transfer. In a circuit, the energy of flowing electrons is being converted into thermal energy. This transfer of energy occurs over a period of time and can be described by a rate of energy transfer. Physicists refer to "power" as the rate of energy transfer over time. Now the equation for power of a circuit is:
P = R*I2.
That is, the power (P) is equal to the resistance (R) of a circuit time the current (I) squared. This is exactly as you have stated, the heat is directly proportional to the resistance and the square of the current.

So the question is, what happens if we decrease the resistance? Resistance and current are related by "Ohm's law",
V = I*R,
that is the voltage potential (V) across a circuit is equal to the current (I) flowing through a circuit times the resistance (R) of the circuit. So if we have a circuit with a constant potential and we decrease the resistance by a factor of 1/2, then the current flowing through it will double. If we try plugging this into the power equation, we'll see that the power of the new reduced resistance circuit increases by a factor of 2 we shown below:

P=(1/2)*R*(2*I)2
P = (1/2)*R*4*I2
P = 2*R*I2

Because the current term is squared in the power equation, the heat given off by the circuit is more highly dependent on the current flowing through it than the resistance. The heat given off by the new reduced resistance circuit increases.

I hope this answers your question.

Regards,


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 © 2017 The Regents of the University of California,
All Rights Reserved.
UCSB Terms of Use