WHAT IS RESISTANCE?

The property of a material that confines the progression of electrons is called resistance.

At the point when a potential difference is applied across a conductor an electric field is set up all through the circuit. The free electrons drift or move  and they crash into the metal particles and their movement is against. More the impact endured by electrons in a conductor more is the opposition (resistance) presented by the conductor.

REASON FOR RESISTANCE

The fundamental reason for opposition(resistance) is because of the crash (or collaboration) of electrons  with the metal particles of the conduit through which they pass.When these electrons slam into them, they move active energy.The electrons lose active energy and slow down.This prompts obstruction.

FACTORS AFFECTING RESISTANCE

A wire’s resistance is determined by four main factors:

Material (Resistivity): 

Certain materials are better at conducting electricity than others.

Additionally, a conductor’s resistance depends on the composition of the material as well as its dimensions.

Larger molecules should make more electrons available, and when the material is densely packed, the electrons will be subjected to more constant collisions, increasing the obstruction.

With a copper wire, electrons can flow freely, but with a steel wire of the same size and shape, they cannot flow efficiently.

Length: 

Resistance is higher in longer wires.

The resistance of a conductor is straightforwardly corresponding to the length of  the conductor. A  long, slim copper wire has  higher  obstruction than a short,thick copper wire.

Thickness (Cross-sectional Area):

Resistance is decreased by thicker wires.

Since electrons can travel through a thick conductor without being struck or captured by an atom, it has the least amount of barrier.

Because electrons encounter higher resistance and have fewer free paths through the conductor, thin conductors have the most blockage.

Temperature: 

A wire’s resistance typically rises when heated.

Temperature frequently affects the resistance of wire resistors and other components.

As the temperature rises, electrons start to vibrate, increasing the particles’ sufficient vibration. Collisions become continuous as a result of their energy expansion, and the conductor’s resistance increases.

RESISTIVITY:

What is resistivity?

How materials are classified based on their resistivity values?

How does resistivity vary with temperature?

RESISTANCE & RESISTIVITY – NUMERICAL 1

Two wires of equal lengths, one of the wires is manganin and the other wire is copper have the same resistance. Which wire will be thinner?

RESISTANCE & RESISTIVITY NUMERICAL -SOLUTION

RESISTANCE & RESISTIVITY – NUMERICAL 2

A conductor of length  is connected to a dc source of potential V. If the length of the conductor is tripled by stretching it. How will the resistance of the conductor be affected?

RESISTANCE AND RESISTIVITY – KEY FORMULAS

Temperature Dependence of Resistance:

R=Ro[1+𝞪(T-To)]

Where,     

R – Resistance at temperature T

Ro – Resistance  at Reference temperature To

𝞪 – Temperature coefficient of resistance

Resistance and Resistivity – Solved Numerical Problems

Problem 1 :Calculating Resistance

A copper wire has a length of 10 m and a cross sectional area of  2x 10^-6 square meter.If the resistivity of the copper is 1.68x 10^-8  Ω-m, find its resistance.

Solution:

R=⍴l/A

R=1.68x 10^-8 x 10/2x 10^-6

R=0.084 Ω

 

RESISTANCE & RESISTIVITY NUMERICAL -SOLUTION

RESISTANCE & RESISTIVITY – NUMERICAL 3

Determine the resistivity of a wire of length 2 m and of resistance 50 Ω having a diameter of 0.6mm

RESISTANCE & RESISTIVITY NUMERICAL -SOLUTION

RESISTANCE OF A MATERIAL

ELECTRICAL RESISTIVITY

LABORATORY METHODS TO FIND THE RESISTIVITY VALUE OF A GIVEN MATERIAL (USING A METER BRIDGE)

RESISTANCE & RESISTIVITY – OHM’S LAW METHOD

Temperature effect on Resistance – Solved numerical problems

Question:

A wire has a resistance of 5 Ω at 2o degree celsius.If its temperature coefficient  𝞪 is 0.004 per degree Celsius, find its resistance at 100 degree Celsius.

Solution:

R=Ro[1+𝞪(T-To)]

Where,     

R – Resistance at temperature T

Ro – Resistance  at Reference temperature To

𝞪 – Temperature coefficient of resistance

R=5[1+0.004(100-20)

R=5(1+0.32)

R=6.6 Ω

Temperature Dependence of Resistance-Practice Questions

S.No.	Question	Answer
1.	A resistor has a resistance of 10 Ω  at 20 degree Celsius. If the temperature coefficient of resistance is 0.004 per degree Celsius.Find its resistance at 100 degree Celsius.	?
2.	A copper wire has a resistance of 50 Ω at 20 degree Celsius. If the temperature coefficient of resistance is 0.004 per degree Celsius .Find its resistance at 80 degree Celsius.	?
3.	A wire has a resistance of  10 Ω at 0 degree Celsius and 12 Ω at 50 degree Celsius.Calculate its temperature coefficient α.	?
4.	A carbon resistor  has R0 =100 Ω at 20 degree Celsius with α= – 0.0005 per degree Celsius.Find its resistance at 60 degree Celsius.	?
5.	A  tungsten wire has R0 =200 Ω at 25 degree Celsius and  R=240 Ω at some temperature T If  α= 0.0045 per degree Celsius,find T	?
6.	An aluminium wire (α= 0.0039 per degree Celsius) and a silver wire (α= 0.0038 per degree Celsius) each have R0 =50 Ω at 30 degree Celsius.Which has higher resistance at 80 degree Celsius ?	?
7.	A wire has a resistance of 5 Ω at 20 degree Celsius. If  its temperature coefficient  α= 0.004 pedigree Celsius.Find its resistance at 100 degree Celsius.	?
8.	A silver wire has a resistance of 2.1 Ω at 27.5 degree Celsius, and a resistance of 2.7 Ω  at 100 degree Celsius.Determine the temperature coefficient of resistivity of silver	?

Temperature Dependence of Resistance- Answers

1	2	3	4	5
13.2 Ω	62 Ω	0.004  per  degree Celsius	98 Ω	69.440 C

 

6	7	8
Al(59.75 Ω) Ag(59.5 Ω) Ans:Al	6.6 Ω	0.00394 per        degree Celsius

Resistance of a Bent Wire: Practice Questions

S.No	Questions	Answer
1.	A wire of resistance 5 Ω is bent into a circle.What is the effective resistance between two diametrically opposite points?	?
2.	A wire of resistance 12 Ω  is bent into a circle.What is the effective resistance between two diametrically opposite points of the circle?	?
3.	A uniform wire of length 2 m and resistance 8 Ω is bent into a square.Find the resistance between two adjacent corners of the square.	?
4.	A wire of resistance 24 Ω is bent into an equilateral triangle.Find the resistance between any two vertices.	?
5.	A uniform wire of resistance 40 Ω is bent into a square. Find the resistance between two diagonally opposite corners.	?
6.	A wire of length L and resistance R is bent into a circle.What is the resistance between two points that subtends at an angle of 900 at the centre.	?
7.	A wire of resistance 36 Ω is bent to form a regular hexagon.Find the resistance between two adjacent vertices.	?
8.	A wire of resistance 60 Ω is bent into a square.Calculate the resistance between midpoints of two adjacent sides.	?
9.	A uniform wire of length l and resistance R is bent into a semicircle.Find the resistance between the ends of the semicircle.	?
10.	A wire of resistance 18 ohms is bent into an equilateral triangle.Find the resistance between any two vertices	?

Resistance of a Bent Wire: Answers

S.No:1	S.No:2	S.No:3	S.No:4	S.No:5
1.25 Ω	3 Ω	1.5 Ω	5.33	10

 

S.No:6	S.No:7	S.No:8	S.No:9	S.No:10
3R/16 Ω	5 Ω	6.25 Ω	R/4 Ω	4 Ω

Calculating Resistivity of a wire -Practice Questions

S.No	Question	Answer
1.	Calculate the resistivity of a material of a wire of 10 m long, 0.4 mm in diameter and having a resistance of 20 Ω	?
2.	Find the resistivity of a conductor in which a current density of 2.5 Am^-2 is found to exist when an electric field of 15 V/m is applied on it	?
3.	A negligible small current is passed through a wire of length15 m and uniform cross-section 6.0x 10^-7 m2, and its resistance is measured to be 5.0 Ω.What is the resistivity of the material at the temperature of the experiment	?
4.	Calculate the resistivity of a material of a wire of 5 m long, 0.45 mm in diameter and having a resistance of 15 Ω	?
5.	Find the resistivity of a conductor in which a current density of 4.0 Am^-2 is found to exist when an electric field of 15 V/m is applied on it	?

Calculating Resistivity of a wire – Answers

S.No:1	S.No:2	S.No:3	S.No:4	S.No:5
2.513×10^–7 Ω.m	6 Ω.m	2.0 x 10^-7 Ω.m	4.77×10^–7 Ω.m	3.75 Ω.m

Conclusion: Resistance and Resistivity Numericals

From simple calculations to more intricate circuit analysis and the consequences of physical changes on resistance, the wide variety of questions has helped you get ready for a variety of variations you may face on the real test.Continue going over these ideas, practise frequently, and do not be afraid to go over any areas where you feel less sure.With commitment and the strong foundation you have established here, you will have no trouble getting a great NEET physics score.

Links to this topic:

NEET Physics: Resistance and Resistivity Practice Questions

The Resistivity of a Wire – A Comprehensive Guide

Resistance of a wire : Factors,Formula, and Practical Applications

‘RESISTIVITY OF THE MATERIAL OF A WIRE/PHYSICS PRACTICAL’