# Why are resistors useful?

1. May 8, 2013

### potatocar

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?

2. May 8, 2013

### bp_psy

And how will you lower the voltage at different points in a circuit?.

3. May 8, 2013

### potatocar

So it's only because the same voltage supply is used for different "things" (that require different currents to flow through them)?

Do you mean if R<1? So.. a resistor can increase the current?

4. May 8, 2013

### bp_psy

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

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.

5. May 8, 2013

### rock.freak667

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.

6. May 8, 2013

### Introyble

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

7. May 8, 2013

### DennisN

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.