How do resistors work? What's inside a resistor? (2022)

How do resistors work? What's inside a resistor? (1)

by Chris Woodford. Last updated: January 2, 2022.

When you first learn about electricity,you discover thatmaterials fall into two basic categories called conductors andinsulators. Conductors (such as metals) let electricity flowthroughthem; insulators (such as plastics and wood) generally do not. Butnothing's quite so simple, is it? Any substance will conductelectricity if you put a big enough voltage across it: even air,which is normally an insulator, suddenly becomes a conductor when apowerful voltage builds up in the clouds—and that's what makeslightning. Rather than talking about conductors and insulators, it'soften clearer to talk about resistance: the ease with whichsomethingwill let electricity flow through it. A conductor has low resistance,while an insulator has much higher resistance. Devices calledresistors let us introduce precisely controlled amounts of resistanceinto electrical circuits. Let's take a closer look at what they areand how they work!

Photo: Four typical resistors sitting side by side in an electronic circuit. A resistor works by converting electrical energy into heat, which is dissipated into the air.

Contents

  1. What is resistance?
  2. Measuring resistance
  3. Resistance is useless?
  4. How resistors work
  5. How does the size of a resistor affect its resistance?
  6. Resistance and temperature
  7. Resistor color codes
  8. Find out more

What is resistance?

Electricity flows through a material carried by electrons,tiny charged particles inside atoms. Broadlyspeaking, materials that conduct electricity well are ones that allow electrons to flow freelythrough them.

In metals, for example, the atoms are locked into asolid, crystalline structure (a bit like a metal climbing frame in aplayground). Although most of the electrons inside these atoms are fixed in place, some can swarm through the structure carrying electricity with them.That's why metals are good conductors: a metal puts up relativelylittle resistance to electrons flowing through it.

(Video) How do resistors work? (Animated) | Basic Electronics

How do resistors work? What's inside a resistor? (2)

Animation: Electrons have to flow through a material to carry electricity through it.The harder it is for electrons to flow, the more resistance there is. Metals generally have low resistancebecause electrons can flow through them quite easily.

Plastics are entirely different. Although often solid, they don't have the samecrystalline structure. Their molecules (which are typically verylong, repetitive chains called polymers) are bonded together in sucha way that the electrons inside the atoms are fully occupied. Thereare, in short, no free electrons that can move about in plasticsto carry an electric current. Plastics are good insulators: they putup a high resistance to electrons flowing through them.

This is all a little vague for a subject like electronics, whichrequires precise control of electric currents. That's why we defineresistance more precisely as the voltage in volts required to make acurrent of 1 amp flow through a circuit. If it takes 500 volts tomake 1 amp flow, the resistance is 500 ohms (written 500 Ω). You mightsee this relationship written out as a mathematical equation:

V = I × R

This is known as Ohm's Law for Germanphysicist Georg Simon Ohm (1789–1854).

Resistance is useless?

How many times have you heard bad guys say that in movies? It's oftentrue in science as well. If a material has a high resistance, itmeans electricity will struggle to get through it. The more theelectricity has to struggle, the more energyis wasted. That soundslike a bad idea, but sometimes resistance is far from "useless"and actually very helpful.

How do resistors work? What's inside a resistor? (3)

Photo: The filament inside an old-style light bulb. It's a very thin wire with a moderate amount of resistance. It's designed to get hot so it glows brightly and gives off light.

In an old-style light bulb, for example,electricity is made to flow through an extremely thin piece of wirecalled a filament. The wire is so thin that the electricityreally has to fight to get through it. That makes the wire extremelyhot—so much so, in fact, that it gives off light. Withoutresistance, light bulbs like this wouldn't function. Of course thedrawback is that we have to waste a huge amount of energy heating upthe filament. Old-style light bulbs like this make light by makingheat and that's why they're called incandescent lamps; newer energy-efficient light bulbs make light without making much heat through the entirely different process of fluorescence.

The heat that filaments make isn't always wasted energy. In appliances like electric kettles, electric radiators,electric showers, coffee makers, and toasters, there are bigger and more durable versions of filaments called heating elements. When an electric current flows through them, they gethot enough to boil your water or cook your bread. In heating elements, at least, resistance is far from useless.

Resistance is also useful in things like transistor radios and TVsets. Suppose you want to lower the volume on your TV. You turnthe volume knob and the sound gets quieter—but how does that happen?The volume knob is actually part of an electronic component called avariable resistor. If you turn the volume down, you're actuallyturning up the resistance in an electrical circuit that drivesthe TV's loudspeaker. When you turn up theresistance, the electriccurrent flowing through the circuit is reduced. With less current,there's less energy to power the loudspeaker—so it sounds muchquieter.

How do resistors work? What's inside a resistor? (4)How do resistors work? What's inside a resistor? (5)

(Video) WHAT ARE RESISTORS?! Why the resistor is so important to electrical circuits and how does it work?

Photo: "Variable resistor" is the very general name for a component whose resistance can be varied bymoving a dial, lever, or control of some sort. More specific kinds of variable resistors include potentiometers (small electronic components with three terminals) and rheostats (usually much larger and made from multiple turns of coiled wire with a sliding contact that moves across the coils to "tap off" some fraction of the resistance). Photos: 1) A small variable resistor acting as the volume control in a transistor radio. 2) Two large rheostats from a power plant. You cansee the dial controls that "tap off" more or less resistance. Photo by Jack Boucher from Historic American Engineering Record courtesy of US Library of Congress.

How resistors work

People who make electric or electronic circuits to do particularjobs often need to introduce precise amounts of resistance. They cando that by adding tiny components called resistors. A resistor is alittle package of resistance: wire it into a circuit and you reducethe current by a precise amount. From the outside, all resistors lookmore or less the same. As you can see in the top photo on this page, and the one below,a resistor is a short, worm-like component with colored stripes onthe side. It has two connections, one on either side, so you can hookit into a circuit.

How do resistors work? What's inside a resistor? (6)

Photo: A typical resistor.

What's going on inside a resistor? If you break one open, andscratch off the outer coating of insulating paint, you might seean insulating ceramic rod running through the middle with copper wire wrapped around the outside. A resistor like this is described as wire-wound. The number of copper turns controls theresistance very precisely: the more copper turns, and the thinner thecopper, the higher the resistance. In smaller-value resistors,designed for lower-power circuits, the copper winding is replaced bya spiral pattern of carbon. Resistors like this are much cheaper tomake and are called carbon-film.Generally, wire-wound resistors are more precise and more stable at higher operating temperatures.

How do resistors work? What's inside a resistor? (7)

Photo: Inside a wire-wound resistor. Break one in half, scratch away the paint, and you can clearly see the insulating ceramic core and the conducting copper wire wrapped around it.

(Video) What is a resistor?

How does the size of a resistor affect its resistance?

Suppose you're trying to force water through a pipe. Different sorts of pipes will be more or less obliging, so a fatter pipe will resist the water less than a thinner one and a shorter pipewill offer less resistance than a longer one. If you fill the pipe with, say, pebbles or sponge, waterwill still trickle through it but much more slowly. In other words, the length, cross-sectional area (the areayou see looking into the pipe to see what's inside), and stuff inside the pipe all affect its resistance to water.

Electrical resistors are very similar—affected by the same three factors. If you make a wire thinner or longer, it's harder for electrons to wiggle through it. And, as we've already seen, it's harder for electricity to flow through some materials (insulators) than others (conductors). Although Georg Ohm is best known for relating voltage, current, and resistance, he also researched the relationshipbetween resistance and the size and type of material from which a resistor is made. That led him to another important equation:

R = ρ × L / A

In simple words, the resistance (R) of a material increases as its length increases (so longer wires offer more resistance) and increases as its area decreases (thinner wires offer more resistance). The resistance is also related to the type of material from which a resistor is made, and that's indicated in this equation by the symbol ρ, which is called the resistivity, and measured in units of Ωm (ohm meters). Different materials have very different resistivities: conductors have much lower resistivity than insulators. At room temperature, aluminum comes in at about 2.8 x 10−8 Ωm, while copper (a better conductor) is significantly lower at 1.7 −8 Ωm. Silicon (a semiconductor) has a resistivity of about 1000 Ωm and glass (a good insulator) measures about 1012 Ωm. You can see from these figures how vastly different conductors and insulators are in their ability to carry electricity: silicon is about 100 billion times worse than copper and glass is about a billion times worse again!

How do resistors work? What's inside a resistor? (8)

Chart: Good conductors: How the resistivity of 10 common metals and alloys compares to that of silver at room temperature. For example, you can see that nichrome, an alloy used in heating elements, has about 66 times more resistance than a similar piece of silver. Data from various sources.

Resistance and temperature

The resistance of a resistor isn't constant, even if it's a certain material of a fixed length and area: it steadily increases as the temperature increases. Why? The hotter a material, the more its atoms or ions jiggle about and the harder it is forelectrons to wriggle through, which translates into higher electrical resistance. Broadly speaking,the resistivity of most materials increases linearly with temperature (so if you increase thetemperature by 10 degrees, the resistivity increases by a certain amount, and if you increase itby another 10 degrees, the resistivity rises by the same amount again). If you cool a material, you lower its resistivity—and if you cool it to an extremely lowtemperature, you can sometimes make the resistivity disappear altogether, in a phenomenon knownas superconductivity.

(Video) How do Resistors Work? - Kipkay Tips

How do resistors work? What's inside a resistor? (9)

Chart: The resistance of a material increases with temperature. This chart shows how resistivity (basic resistance of a material, independent of its length or area) increases almost linearly as the temperature increases from absolute zero up to about 600K (327°C) for four common metals. Drawn using original data from "Electrical Resistivity of Selected Elements" by P. Desai et al, J. Phys. Chem. Ref. Data, Vol 13, No 4, 1984 and "Electrical Resistivity of Copper, Gold, Palladium, and Silver" by R. Matula, J. Phys. Chem. Ref. Data, Vol 8, No 4, 1979, courtesy of US National Institute of Standards and Technology Open Data.

(Video) How to use a Resistor - Basic electronics engineering

Find out more

Related articles on our site

  • Capacitors
  • Diodes and light-emitting diodes (LEDs)
  • Electricity
  • Electronics
  • Heating elements
  • Transistors

Videos

  • MAKE Presents: The Resistor: A 5-minute introductory video from Colin Cunningham of MAKE magazine. Covers the basic concept of resistors and a little history, then shows how to make your own resistor with a 2B pencil!
  • What is a resistor?: This video spends quite a bit of time explaining how to read color codes; if you find the whole color system confusing, this is a good place to get your ideas clear.

Books

For younger readers

  • Easy Electronics by Charles Platt. Maker Media, 2017. A simplified, comic-style, 50-page introduction with an emphasis on learning by doing.

For older readers

Articles

FAQs

What is inside a resistor? ›

Resistor Composition

Most common, modern resistors are made out of either a carbon, metal, or metal-oxide film. In these resistors, a thin film of conductive (though still resistive) material is wrapped in a helix around and covered by an insulating material.

How does a resistor work? ›

Because the resistor's job is simply to limit how quickly the electrons are flowing through the circuit as a whole, a resistor can be placed anywhere in the sequence (series) of components. From anywhere along the circuit, the resistor will slow the flow of electrons.

What goes through a resistor? ›

In Figure 10.3. 2, the current coming from the voltage source flows through each resistor, so the current through each resistor is the same. The current through the circuit depends on the voltage supplied by the voltage source and the resistance of the resistors.

What are 3 purposes of a resistor? ›

Resistors are used for many purposes. A few examples include limiting electric current, voltage division, heat generation, matching and loading circuits, gain control, and setting time constants.

How does resistance work in a circuit? ›

Resistance serves as an indicator that quantifies how readily current will flow in a circuit using ohms (Ω) as the unit. Current increases when resistance decreases, and it decreases when resistance increases. Resistors are essential in order to ensure that current flows at the appropriate level in circuits.

What's inside a ceramic resistor? ›

Ceramic resistors are made of a combination of finely powdered carbon and ceramic material. These two powders combine in specific ratios to determine the final value of the resistor. The higher ratio of carbon in the mix, the lower resistive valve the ceramic resistor will have.

What do resistors do to voltage? ›

The resistor will create a voltage drop by slowing down, or resisting, the electrons as they try to flow through the resistor. If a component receives too much voltage, it may be damaged or not function properly.

Why do resistors get hot? ›

When a resistor is placed under a voltage that approaches the upper limits of its power rating, the resistor generates more heat than normal. This is due to the voltage attempting to force more current (electrons) through the resistor than it is designed to pass.

Do resistors use power? ›

The resistor "consumes" power (not current) and that power is the product of voltage across the resistor times the current flowing.

How does current flow in a resistor? ›

According to Ohm's Law, 3.7 mA of current will flow down across the resistor. 1 mA exactly the same as 0.001 A, just like 1 mm is the same as 0.001 m. In this circuit, current flows clockwise from the + terminal of the battery, down across the resistor, and then back to the – terminal of the battery.

What happens to current through a resistor? ›

We all know that in a series circuit, the current is the same for all of the elements. But when the current flow through a resistor, what does it lose? The current is the same because it doesn't lose the numbers of charges.

Does resistor change voltage or current? ›

So following the law a resistor must affect both voltage and current however the reality is that it only changes one size. you also find use cases where only voltage is affected.

What are the 4 types of resistors? ›

Types of Resistors
  • Fixed Value Resistors. These are the predominant type of resistor configuration, and as the name suggests, they have a fixed resistance value. ...
  • Variable Resistors. ...
  • Resistor Networks. ...
  • Carbon Film Resistors. ...
  • Metal Film Resistors. ...
  • Wirewound Resistors. ...
  • Metal Oxide Resistors. ...
  • Metal Strip Resistors.

Why do you need resistors in a circuit? ›

A resistor is a two-terminal electrical component that provides electrical resistance. In electronic circuits, resistors are predominantly used to lower the flow of current, divide voltages, block transmission signals, and bias active elements.

What is resistor and it's function? ›

Resistor is defined as. A passive electrical component with two terminals that are used for either limiting or regulating the flow of electric current in electrical circuits. The main purpose of resistor is to reduce the current flow and to lower the voltage in any particular portion of the circuit.

How is resistance caused? ›

cause of the resistance of a wire: Resistance of a given conducting wire is due to the collisions of free electrons with each other, the ions or atoms of the conductor and the walls of the conductor during their drift towards the positive end of the conductor which in turn depends upon the arrangements of atoms in the ...

Do resistors only work one way? ›

After all, many capacitors, which are sometimes confused for resistors, are polarized and must be placed properly within a circuit. But resistors have no polarity. Current passes equally through from either direction. That means you can't install them backward.

Is a light bulb a resistor? ›

The reason a light bulb glows is that electricity is forced through tungsten, which is a resistor.

What is inside a carbon resistor? ›

The carbon resistor contains carbon coated onto a ceramic core. A spiral is etched on the deposited carbon, which turns it into a wire wound on a ceramic core.

How do you make a resistor? ›

How To Make A Wire Wound Resistor - YouTube

What can be used to replace a resistor? ›

A good conductor, such as metal wire, can be used as a Resistor. Resistance can be adjusted by limiting the thickness of the wire or decreasing the path through it.

What happens if there is no resistor in a circuit? ›

If there really were no resistance in the circuit, the electrons would go around the circuit, and arrive back at the beginning of the circuit with as much energy as the potential difference (the voltage). That final energy is usually what is dissipated as heat or other types of energy by the circuit.

Do resistors drop current? ›

The current after a resistor is the exact same as it was before the resistor. “But doesn't the resistor reduce the current?” Yes, it does. A circuit always has a bit of resistance, no matter if it has resistors or not in it.

Why do resistors slow current? ›

As electrons move through the resistor they collide with the atoms and molecules of the resistor material. That briefly causes them to slow down a bit (losing kinetic energy), but then they speed up again (gain kinetic energy) due to the energy supplied by the electric field of the battery.

What causes a resistor to fail? ›

A fixed composition resistor normally fails in an open configuration when overheated or overly stressed due to shock or vibration. Excessive humidity may cause an increase in resistance. A variable composition resistor may wear after extensive use, and worn away particles may cause high resistance short circuits.

What happens if a resistor fails? ›

When a resistor fails, it usually gets charred or burns. As a result, it either stops conducting the electrical current/signal or does not resist the current flow.

Do resistors lose resistance over time? ›

If heat is dissipated and the temperature falls back within specified limits the resistance value should return to its expected value. But repeated temperature excursions will eventually degrade the resistor performance. High moisture content in the environment can degrade the resistor performance.

How much heat does a resistor produce? ›

Thus, a current of one ampere flowing through a resistor across a voltage drop of one volt produces one watt of heat.

How much current can a resistor handle? ›

The power rating of a resistor is measured in watts, and it's usually somewhere between ⅛W (0.125W) and 1W. Resistors with power ratings of more than 1W are usually referred to as power resistors, and are used specifically for their power dissipating abilities.

Does a resistor increase battery life? ›

Since the voltage doesn't change, when the resistance goes up, the current and the power go down. So, adding series resistance to the circuit will make your battery last longer.

Does resistance change voltage? ›

Ohm's law states that current is directly proportional to voltage but inversely proportional to resistance. At constant resistance, current increases as voltage increases and vice versa. At constant voltage, current decreases as resistance increases and vice versa.

Can you have current without voltage? ›

Voltage is sometimes described as the 'push' or 'force' of the electricity, it isn't really a force but this may help you to imagine what is happening. It is possible to have voltage without current, but current cannot flow without voltage.

Does resistance decrease voltage? ›

Voltage varies directly with current. "R" is the constant of proportionality telling how much it varies. If I add in a resistor to a circuit, the voltage decreases. If you have a resistor in a circuit, with a current flowing through it, there will be a voltage dropped across the resistor (as given by Ohm's law).

What is the difference between resistance and resistor? ›

Resistance is the property of a conductor, which determines the quantity of current that passes through it when a potential difference is applied across it. A resistor is a electrical componet with a predetermined electrical resistance, like 1 ohm, 10 ohms 100 ohms 10000 ohms etc.

What happens when you add a resistor to a series circuit? ›

As the number of resistors in a series circuit increases, the overall resistance increases and the current in the circuit decreases.

Does temperature affect a resistor? ›

Increasing the temperature (typically) increases resistance. The temperature coefficient of resistance (TCR) of wire or a resistor relates the change in resistance to the change in temperature.

Do resistors cause voltage drop? ›

The larger the resistor, the more energy used by that resistor, and the bigger the voltage drop across that resistor. Ohm's Law can be used to verify voltage drop. In a DC circuit, voltage equals current multiplied by resistance.

What is inside a carbon resistor? ›

The carbon resistor contains carbon coated onto a ceramic core. A spiral is etched on the deposited carbon, which turns it into a wire wound on a ceramic core.

What kind of component is a resistor? ›

A resistor is an electrical component that restricts the flow of electrical current in a circuit. The analogy often used to explain its operation is to consider current as water flowing in a hosepipe; a resistor can be considered as a constriction in the pipe that limits the flow of water.

What is inside a capacitor? ›

What is Inside a Capacitor? - YouTube

Is a resistor a conductor or insulator? ›

Resistors. Resistors are made of materials that conduct electricity, but offer opposition to current flow. These types of materials are also called semiconductors because they are neither good conductors nor good insulators.

Why is a resistor made of carbon? ›

The big advantage of carbon composition resistors is their ability to withstand high energy pulses. When current flows through the resistor, the entire carbon composition body conducts the energy. The wirewound resistor, for example, has a much smaller volume of wire to conduct current.

What is resistor color code? ›

The colour code used to denote the tolerance rating of a resistor is given as: Brown = 1%, Red = 2%, Gold = 5%, Silver = 10 % If resistor has no fourth tolerance band then the default tolerance would be at 20%.

Why is carbon made up of resistance? ›

One of the most significant benefits of the Carbon resistor is that it can withstand high energy pulses. The entire body of the carbon resistor conducts the energy when the current flows through it. The carbon resistors are cheaper to make and can have a higher resistance than of wire-wound resistors.

What do resistors do to voltage? ›

The resistor will create a voltage drop by slowing down, or resisting, the electrons as they try to flow through the resistor. If a component receives too much voltage, it may be damaged or not function properly.

Is a light bulb a resistor? ›

The reason a light bulb glows is that electricity is forced through tungsten, which is a resistor.

Is a battery a resistor? ›

A battery is a real-life voltage source. A battery can be thought of as a perfect voltage source with a small resistor (called internal resistance) in series.

Do resistors store energy? ›

Resistor does not stores the energy. It dissipates the energy. An inductor is used to store energy in the form of a magnetic field. A capacitor is used to store the energy in the form of electric charge.

Do capacitors have oil? ›

Oil-Filled Capacitors supplied today contain non-PCB oil and are a UL recognized component. Oil-Filled capacitorsare only supplied with ballasts where the capacitor operating voltage cannot be satisfied by Dry Film Capacitors.

What liquid is inside a capacitor? ›

Electrolyte. The electrolytic capacitor got its name from the electrolyte, the conductive liquid inside the capacitor.

Do resistors waste energy? ›

Yes, and no. When current passes through the resistor, it generates heat and therefore wastes energy. However, if you took the resistor out (and therefore drove the LED at a higher voltage) you'd be driving more current through the circuit and thus actually burning more power than with the resister in place.

What causes resistance? ›

An electric current flows when electrons move through a conductor, such as a metal wire. The moving electrons can collide with the ions in the metal. This makes it more difficult for the current to flow, and causes resistance.

Do resistors have polarity? ›

It's easy to understand why you might be concerned. After all, many capacitors, which are sometimes confused for resistors, are polarized and must be placed properly within a circuit. But resistors have no polarity. Current passes equally through from either direction.

Videos

1. How they are made: Resistors
(OPENBOX Education)
2. How to use "Resistors" in Circuits : Tutorial
(Gadgetronicx)
3. What's inside Resistors ?
(Createch)
4. Speed of Electrons – What’s a Resistor (ElectroBOOM101-004)
(ElectroBOOM)
5. ELECTRONICS BASICS #1 RESISTORS EXPLAINED
(TEKNOISTIX)
6. Variable resistors, how they work and what they do: fizzics.org
(Fizzics Organisation)

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