Question

A certain wire has a resistance of 110 Ω. What is the resistance of a second wire, made of the same material, that is 1/4 as long and has 1/3 the diameter?

Answer 1

Answer: 247.5 ohms

Explanation: Since the two wires are of the same materials, their resistivity will be the same. Find solution attached.

Answer 2

Answer:

New Resistance = 247.5 ohm

Explanation:

Resistance = resistivity * length / area

Since resistivity for the material is constant, resistance is directly proportional to (length/area).

This means that if (length/area) decreases or increases by any ratio, then resistance will increase or decrease by the same ratio.

So let's find the change in length/area

New length = 0.25 old length

New area = (1/9) old area                                 (This is because area equation contains a square of the diameter. if diameter decreases by 1/3, area decreases by (1/3)^2   )

So we now get length /area:

New length / new area = ( 0.25 old length) / (1/9 of old area)

New length / new area = 9*0.25 (old length / old area)

New length / new area = 2.25 (old length / old area)

To get the new resistance, we simply multiply it by the ratio we just found.

This equals:

110 * 2.25 = 247.5 ohm