How is the resistance R, of a wire related to its diameter, d?
Question
How is the resistance R, of a wire related to its diameter, d?
Solution
The resistance (R) of a wire is inversely proportional to its cross-sectional area (A). This relationship is expressed by the formula:
R = ρL/A
where:
- R is the resistance,
- ρ (rho) is the resistivity of the material,
- L is the length of the wire,
- A is the cross-sectional area of the wire.
The cross-sectional area (A) of a wire can be calculated using the formula for the area of a circle (since the cross-section of a wire is a circle), which is:
A = π(d/2)^2
where:
- d is the diameter of the wire.
Substituting the second equation into the first gives:
R = ρL/(π(d/2)^2)
So, the resistance of a wire is inversely proportional to the square of its diameter. If the diameter of the wire is doubled, the resistance will be reduced by a factor of four (assuming the length and the material of the wire remain constant).
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