# Explain to me what resistors do?

1. Oct 5, 2004

### Maxwell

Can someone please explain to me what resistors do? And why we use them.

Thank you.

2. Oct 6, 2004

### chroot

Staff Emeritus
They resist the flow of electrical current, producing heat. We use them for many reasons; water heaters, electric stoves, and toaster ovens actually use resistors specifically to create heat. Resistors are also (speaking loosely) used to keep electrcity from going where it is not wanted in a circuit.

- Warren

3. Oct 6, 2004

### Gokul43201

Staff Emeritus
Resistors are also used to adjust the gain of an amplifier, help drive capacitive loads, adjust time constants, etc.

4. Oct 6, 2004

### Maxwell

So basically you'd really only use a resistor in a circuit that will produce heat, or need to build up heat?

Examples - Toaster, Oven, Gain on an amplifier.

Is that right, for a basic definition/function?

5. Oct 6, 2004

### Gokul43201

Staff Emeritus
No, it's not. That's why I provided examples that do not do this.

Amplifier gain is a ratio of voltages, and has little connection to heat. Besides dissipating electrostatic energy in the form of heat, resistors provide a potential (voltage) difference across their ends. Having the right voltages at different parts of a circuit requires the use of resistors.

6. Oct 6, 2004

### Cliff_J

Maxwell - look up ohms law online.

Basically, its this simple equation:

voltage = current * resistance

Since those are all linked by that equation, if a person wanted to control voltage or current you can change the value of a resistor.

Cliff

7. Oct 12, 2004

### Dual Op Amp

Imagine a light bulb, it is connected to a 9 volt battery, but the light bulb is only rated for 2.5 volts. If I connected the batter straight to the bulb, it would flash, and burn out. To prevent this, I would connect a resistor in the circuit, it would restist the flow of current, and cause a voltage drop. This resistor would be the exact value, so it would bring the voltage down to 2.5, and that would propperly light the bulb. Electrons from a power source are constantly colliding with atoms in the wire or load. This makes the atom positivly charged, so it ejects another electron. The resistance determines how much energy the ejected electron has. As the electron collides with the atom, some of the energy is converted into heat (vibrational) energy. The resistance of the molecules determines how much energy is converted back into kinetic energy for the ejected electron. Some energy is also converted into light energy, this is purposely used in light bulbs, making light bulbs resistors.

8. Oct 14, 2004

### kissme

may i ask u , how old are u ? (maxwell )