Which one of the following materials is useful for making bulb filaments ?
Correct answer: D. tungsten
- A. constantan
- B. nichrome
- C. copper
- D. tungsten
Explanation
Tungsten is used for bulb filaments because it has a very high melting point and can become white-hot without melting. Option c, copper, is a good conductor but has a much lower melting point and is unsuitable for a glowing filament.
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About Resistance and Resistivity
Resistance measures opposition to current in a conductor and follows R = V/I for an ohmic conductor, while resistivity is an intrinsic property of the material. Questions use R = ρL/A, examine effects of length, cross-sectional area and temperature, and distinguish resistance, resistivity, conductance and conductivity.
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