Relation between Resistance and Length

In physics, resistance is the opposition offered to the flow of electricity. Length, on the other hand, is the physicalย dimensional measurement of extension between two points. The relation between length and resistivity is given by the resistivity formula. Resistance is directly proportional to the length. This means that any change in the length of the material will change its value of resistance.

Table of Contents

Resistivity Formula

The resistance and length relation can be mathematically expressed as follows-

\(\begin{array}{l}R= \frac{\rho L}{A}\end{array} \)

Where,

  • R is the resistance measured using ohms.
  • L is the length of the material measured using the meter.
  • A is the cross-sectional area measured in m2.
  • ๐œŒ is the resistivity of the material measured using ohm-metre

Resistance And Length Relation

For a given material,the resistance and length formula clearly speaks that the resistance is directly proportional to its length.

\(\begin{array}{l}R\propto L\end{array} \)

This implies that-

  • When the length of the material is increased, its value of resistance also increases.
  • When the length of the material decreases, its value of resistance will also decrease.

Resistance And Length Formula

The resistivity formula can be rearranged to get the relation between resistance and length. In short, It can be expressed along with symbols and units of resistance and length as-

Formula Symbol Unit

Resistance

\(\begin{array}{l}R= \frac{\rho L}{A}\end{array} \)
R Ohm

Length

\(\begin{array}{l}L=\frac{RA}{\rho }\end{array} \)
L Meter

Practice Question

Calculate the value of resistance of a 2-meter-long wire with a cross-sectional area 1.7ร—10-5m2 and resistivity 1.86ร—10-7Ohm-metre.

Given,

Length of the wire L = 2 m

Cross-sectional area A = 1.7ร—10-5m2

Resistivity ๐œŒ = 1.86ร—10-7Ohm/meter.

Substituting the values in the resistance and length formula got by rearranging the resistivity formula we get-

\(\begin{array}{l}R= \frac{\rho L}{A}\end{array} \)
\(\begin{array}{l}\Rightarrow R= \frac{1.86\times 10^{-7} \times2.0 }{1.7\times 10^{-5}}\end{array} \)
\(\begin{array}{l}\Rightarrow R= 2.188\times 10^{-2}\end{array} \)

Thus, the resistance of the wire is 2.188ร—10-2ohms.

Watch the video and solve important questions in the chapter Electricity Class 10

Hope you understood the relation and conversion between resistance and length of any material.

Physics Related Topics:

Relation between Line Voltage and Phase Voltage
Relation Between Ev And Joule
Relation Between Watt And Volt
Relation Between Power And Resistance

Frequently Asked Questions โ€“ FAQs

Q1

What is resistance?

Resistance is the measure of opposition to current flow in a circuit. Its SI unit is ohm.
Q2

What is resistivity?

Resistivity is the resistance generated by the substance per unit distance for a unit cross-section. Its SI unit is ohm-m.
Q3

What is electric current?

Electric current is the rate of flow of electrons inside a conductor. Its SI unit is ampere.
Q4

What happens to the resistance of a wire if its length is decreased?

As resistance is directly proportional to the length of the conductor, the resistance will decrease with the decrease in the length of the wire.

The video demonstrates the waterpipe analogy and explains the factors that affect the flow of current.

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