# Why are resistors useful?

According to Wikipedia,

A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active elements, and terminate transmission lines, among other uses.

However, it's difficult for me to find any resources as to why reducing current flow, or dividing voltages, is useful in the first place. The Wikipedia source came up google searching "Why are resistors useful?" Which only served to explain what they did, but not explain why what they're doing is beneficial. This may be a very basic and trivial question, but I genuinely don't know.

• If you have a circuit component that can handle a maximum of 1.5mA current, but you design the circuit such that it gets 3A, your component will simply get destroyed (might catch fire also). Feb 18 '18 at 16:01
• A light bulb is a resistor. Feb 18 '18 at 16:35
• @knzhou Well given the fact that I’m wondering why its description of its uses are beneficial, that answer doesn’t help me understand them any better. Feb 18 '18 at 16:36
• Think about discrete components like a PNP transistor, they work because the potential difference between the various terminals have particular values.
– jim
Feb 18 '18 at 18:21

Conductors have a very small resistivity, typically on the order of $10^{-8} \Omega m$. If you apply a voltage across a conductor without adding resistors, the current would be very large. Such large currents flowing through a conductor would heat up the conductor rapidly, potentially causing fires.

• And is an example of a conductor in this context like a copper wire? Feb 18 '18 at 16:09
• Yes that's correct. Feb 18 '18 at 16:14

Dividing voltages is very useful. A fairly simple and common example is a potentiometer, used to control the voltage with a rotating dial or linear fader. You see that a lot with knobs and sliders (say for example, audio equipment). I'm sure you can find far more complicated uses of voltage dividers; but I'm not too well versed in electronics.

Another important thing to consider about resistors is their theoretical importance in circuits. Resistors can be used to model other circuit elements as well, such as incandescent lightbulbs and heating elements.

As others mentioned, they can also just in general be used to reduce currents. This can be extremely useful, so that with a single voltage for example, you can power many different components of a wide array of voltage and amperage requirements. Think modern electronics, which have many different small parts.

It is also used heavily in control systems engineering as part of tuning the response. Resistors are an ideal mathematical circuit element, like capacitors, inductors, voltage sources, etc. They are used in the mathematical model to get the proper responses using differential equations or by analyzing the state space of the complex system.

See resistors are required to reduced the current in the circuit. In some situations we require low value of current to run our devices (lets say 50amp) but we are provided with high current(assume100amp) which can destruct our gadgets. So to get require amount of current it is reduced with the help of resistors. Their are alt. ways such as adding a component in parallel but it becomes sometimes too complicated so we use resistor to make it easy.