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# Resistivity and conductivity

Let's look at the properties of materials that cause a resistor to resist the flow of current. Explore the principles of Ohm's law, resistance, and resistivity in electrical circuits. Understand how resistance is defined by voltage and current, and how it remains constant in Ohmic materials. Discover the factors that influence resistance, including the length, cross-sectional area, and material of a resistor. Created by David SantoPietro.

## Want to join the conversation?

• How does length affect resistivity
• Length affects the overall resistance of a resistor. The longer a resistor, the further electrons have to travel through that resistor. This will increase resistance because the electrons will be affected by resistor for a longer period of time as they travel through it.
• Does resistivity depend on temperature ? If so, how?
• Good question and yes it definitely does depend on temperature. As matter gets hotter, the atoms jiggle about more and that extra jiggling increases the number of scattering events a charge will experience as it conducts current. Each scattering event will slow the motion of the charges and thus reduce the current flowing.

https://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity#Temperature_dependence
• Does this "wire resistance" happens also with ethernet cables? So the shorter the ethernet cable the better?
• yes; the sorter the less resistance so thats good thinking....

BUT also, the quality of digital data that passes through a cable can get 'reduced'. so shorter is better for accuracy of communication / signal
• Would conductance = σ(conductivity) * L/A
• You have the right idea. But, keep in mind that increasing the area of the material would increase the conductance and decreasing the length will also increase its conductance, because conductance works in the opposite to resistance.

So, the formula becomes:

G(conductance) = σ(conductivity)*A/L
• Why does the current increase if we increase the voltage or the potential difference?
• Hello Rutwik,

Perhaps it would be better to ask what causes current to flow in the first place.

I made these videos to help answer questions about voltage and current. The second video may help you visualize the situation but you'll need to watch the first video first...

Regards,

APD
• Sir , could you please explain me the difference between resistance and resistivity ?
• Hello Ambati,

A resistor is a physical electrical component. It exists to convert electrical energy into heat.

Resistivity is a description of a material. It describes how the material will resist the flow of electrical current.

We could put the two together in a sentence. A resistor is manufactured using a carbon core. The resistance of this resistor will depend on the resistivity of the carbon core, the length of the core, and the cross sectional area of the core.

https://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity

Regards,

APD
• If the resistor slows down electrons, then how come the current is the same before the resistor and after the resistor?

Shouldnt the current be less after the resistor?
(1 vote)
• This is a misconception. Resistors DO NOT slow down electrons as they enter. Resistors simply limit the amount of current that flows through the circuit. Here is an analogy: Think of a racetrack that is filled with cars driving around in circles. There is no room for an extra car. Assuming that these cars are moving, all the cars must be moving at the exact same speed, otherwise they are going to crash. The same thing applies to the flow of current. The current must be uniform throughout the circuit. As for resistors limiting the current, here is an example:

Suppose you have a 12 V battery and you wire it up to a simple circuit with a
2Ω resistor. By Ohm's law, the current must 6 A. The current at any point in the circuit will be 6 A. Now, let's say that you remove the 2Ω resistor and replace it with a 3Ω resistor. Now, using Ohm's law you can find that the current must be 4 A. The current is still the same at all points in the circuit, but the larger resistance allows less current to flow. Hope this helps!
• Why do resistance happen?
• Resistance is the word we use for how well an object tries to resist, or you could think "slow down", a current that flows through it. Maybe you can think of resistance as a sort of squeezing. If you make one of your hands into a tube and stick a finger inside it, it goes in easily if your tube-hand is relaxed. However, when you start squeezing your tube-hand, it takes a lot more energy and time for the finger to go through. Resistance in circuits arises because the atoms that make up the substance that the current is flowing through collide with the stream of electrons and mess up their motion.
• How does the cross-sectional area affect resistivity?
Does temperature affect resistivity?
• Incr. the cross-sectional area decr. the resistance and vice-versa. As for temperature effects, it depends. If we are dealing with a perfect conductor, decr. the temperature incr. the resistivity and consequently, the resistance. However, semiconductors, on decr. the temperature have lower resistivities. This is why superconductors are generally designed to be super-cooled semiconductors. Of course, technology keeps improving and this will not be so forever.

Note: Thanks to lingling40hrs for noticing my mistake.
• I still don't understand how area affects resistivity. Why should area matter?
• Hello Alex,

This is "cross sectional" area.

Think of it as a pipe. A small pipe has a small cross sectional area while a "big" pipe has a large cross sectional area. The large pipe will have a lower resistance to the flow of current.

Regards,

APD