Which one of the following physical quantities does NOT affect the resistance of a cylindrical resistor ?
- A.The current through it
- B.Its length
- C.The resistivity of the material used in the resistor
- D.The area of cross-section of the cylinder
Correct answer
Explanation
The correct answer is A, The current through it. The resistance of a conductor depends on its material and shape, not on how much current flows through it.
For a cylindrical conductor, R = ρL/A, where ρ is the resistivity of the material, L the length and A the area of cross-section. Doubling the length doubles the resistance, and doubling the area halves it. Resistivity is a property of the material: low for silver and copper, high for nichrome, which is why nichrome is used in heater coils. By Ohm's law, V = IR, changing the voltage changes the current, but R itself stays fixed as long as the temperature does not change.
B is wrong: resistance is directly proportional to length. C is wrong: resistance is directly proportional to the resistivity of the material. D is wrong: resistance is inversely proportional to the area of cross-section, so a thick wire has less resistance than a thin one.
Exam tip: R = ρL/A; resistance depends on material, length, thickness and temperature, but not on current or voltage.
Practice Questions
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- B.Martin Luther
- C.Johannes Kepler
- D.Copernicus
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- B.Objective lens-Condenser-Body tube-Eyepiece
- C.Condenser-Objective lens-Body tube-Eyepiece
- D.Eyepiece-Objective lens-Body tube-Mirror
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- B.Histones are proteins that are present in nucleus in association with DNA.
- C.Histones are proteins associated with lipids in the cytosol.
- D.Histones are proteins associated with carbohydrates in the cytosol.
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