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Power drain in circuits 
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#1
Feb1514, 09:56 AM

P: 8

Alright, so, is my thinking correct in that:
1. Within a series circuit, a larger resistor will drain more power than a smaller resistor. 2. Within a parallel circuit, a smaller resistor will drain more power than a larger resistor. 3. Between two circuits, each with the same voltage source, the one with a smaller equivalent resistance will drain more power. I'm doing some MCAT prep and for some reason the power drain concept is difficult for me but I've think I've got the hang of it now. Any thoughts? 


#2
Feb1514, 10:40 AM

Sci Advisor
HW Helper
Thanks
P: 26,148

Hi PStudent111!
Yes. The easy way to check this is … For 2 and 3, the voltage (V) is the same, so you use P = IV = V^{2}/R, which is inversely proportional to R. 


#3
Feb1514, 01:00 PM

P: 3,135

For example suppose you changed the resistor to one with an exceptionally high resistance, Lets say you replaced it with a 1m air gap. Virtually no current would flow through the 1m air gap so the power loss would approach zero. However no power would be delivered to the load either so it wouldn't be a very useful circuit. Instead of using the word "drain" it might be better to use the word "dissipate". 


#4
Feb1514, 02:05 PM

Mentor
P: 11,823

Power drain in circuits



#5
Feb1614, 05:21 AM

P: 3,135

Perhaps. He did say "a larger" rather than "the larger".



#6
Feb1614, 06:04 AM

Sci Advisor
Thanks
PF Gold
P: 12,123

This is a good example of where some calculations are better than arm waving. If you draw the circuit out, specifying the conditions ( supply voltage, resistor values etc.) and work out the current and power for the supply and the various resistors in the circuit, for various values, you will see the pattern. I mean work the values out yourself and not use an emulator. The sums are easy enough.
Of course, using symbols rather than numbers, the algebra will give you a better idea of what is happening  but it is not necessary if you really don't like Maths. 


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