One Hundred meters of a certain type of wire has a resistance of 7.2 ohms. What is the resistance of 2.5 m of this wire? a. 18 ohm b. 1.8 ohm c. 0.18 ohm d. 3.0 ohm e. 0.30 ohm

The resistance of 2.5 m wire is 0.18 ohm.

Option C.

Explanation:

Resistance is the measure of obstacle given to the flow of currrent. As per ohm's law, resistance is the constant of proportionality between voltage and current. But the resistance of each circuit depends upon the nature of resistor used in that circuit.

R =

So the resistance depends upon the resistivity of the material, length of the material and inversely proportional to the cross sectional area of the material.

In this case, the length of the wire is varied and the composition and cross section is kept constant. From the formula, it can be seen that resistance is directly proportional to the length of the resistor. So if the wire acting as resistor undergoes a decrease in length from 100 m to 2.5 m then there will be decrease in the resistance of the wire also.

Let be the resistance of 100 m wire and be the resistance of 2.5 m wire.

Then, , remaining all parameters will get canceled out due to the usage of same wire with same cross sectional area.

So,

So the resistance of 2.5 m wire is 0.18 ohm.

d) physical means can be used to separate the components of air.