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Why are resistors useful?

by potatocar
Tags: resistors
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potatocar
#1
May8-13, 04:53 AM
P: 8
I don't understand why we use resistors at all. I've read that they cause a voltage drop and decrease the flow of electrons (current). Why is this useful? If we want to decrease the current, why not just lower the voltage? Don't resistors just waste energy?
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bp_psy
#2
May8-13, 05:02 AM
P: 452
Quote Quote by potatocar View Post
Why is this useful? If we want to decrease the current, why not just lower the voltage? Don't resistors just waste energy?
And how will you lower the voltage at different points in a circuit?.
potatocar
#3
May8-13, 05:10 AM
P: 8
Quote Quote by bp_psy View Post
And how will you lower the voltage at different points in a circuit?. .
So it's only because the same voltage supply is used for different "things" (that require different currents to flow through them)?

Also notice that ohms law gives very high currents for very low resistances even if your voltages are low. Of course ohm law doesn't always hold but it still gives you a good idea
Do you mean if R<1? So.. a resistor can increase the current?

bp_psy
#4
May8-13, 05:24 AM
P: 452
Why are resistors useful?

Quote Quote by potatocar View Post
So it's only because the same voltage supply is used for different "things" (that require different currents to flow through them)?
Yes the main use of resistors is voltage control and current control.
http://en.wikipedia.org/wiki/Current_divider
http://en.wikipedia.org/wiki/Voltage_divider

Quote Quote by potatocar View Post
Do you mean if R<1? So.. a resistor can increase the current?
The current always decreases with increasing R. What I meant was that it would be very hard to adjust the current in a low resistance circuit just by adjusting the voltage. I edited that out because It might be confusing and maybe not a very useful way to think about it.
rock.freak667
#5
May8-13, 07:10 AM
HW Helper
P: 6,202
Quote Quote by potatocar View Post
I don't understand why we use resistors at all. I've read that they cause a voltage drop and decrease the flow of electrons (current). Why is this useful? If we want to decrease the current, why not just lower the voltage? Don't resistors just waste energy?
Resistors are also useful in generating heat. For a current I through a resistance R, the powerloss is P = I2R which manifests itself through heat (this is how circuits overheat and stop working or burn). Using this idea, you can use this heat in applications such as light bulbs, electric stoves, soldering irons and so on.
Introyble
#6
May8-13, 06:38 PM
P: 33
A perfect circuit would encounter zero resistance. Love to see somebody build it. You would be a trillionaire. Power my AC with no resistance LOL
DennisN
#7
May8-13, 07:44 PM
DennisN's Avatar
P: 483
Some more advanced uses (in AC filter circuits):
(R=Resistor, C=Capacitor)

With these types of circuits you can filter out various frequency bands; this is what equalizers do.


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