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Physics
Resistance in a wire
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R = ρL / A0.667 Ω
Drag L horizontally; drag A vertically on the cross section.
Ω·cm
cm
cm²
Units: ρ in Ω·cm, L in cm, A in cm² → R in Ω.
Each situation compares with the default wire.
R = ρL / A
Ω
0.5 × 10 / 7.5
Keep a reference, then change one variable.
With the other variables fixed: double L or ρ and R doubles. Double A and R halves. Doubling the diameter makes A four times larger, so R falls to one quarter.
Model notes
- Uniform cylindrical wire at constant temperature; R = ρL/A. No contact resistance, heating or temperature dependence is simulated.
- The parameter ranges illustrate the relationship. No specific material is assigned to a resistivity value. The cylinder and enlarged cross section have independent drawing scales.
- A denotes cross-sectional area, often written S in Vietnamese textbooks. 1 Ω·cm = 0.01 Ω·m; 1 cm² = 0.0001 m².