In an incandescent electric bulb, the filament of the bulb is made up of which metal?
- A.Aluminium
- B.Copper
- C.Tungsten
- D.Silver
Correct answer
Explanation
The correct answer is C, Tungsten. Tungsten is used for the filament because it has the highest melting point of all metals, about 3,422°C, and can glow white-hot without melting.
An incandescent bulb works by passing current through a thin, coiled filament of high resistance until it becomes hot enough to give out light. Tungsten also evaporates very slowly at high temperature, so the filament lasts. The bulb is filled with an inert gas such as argon or nitrogen, or emptied of air, to stop the hot tungsten from reacting with oxygen and burning out. Most of the energy still turns into heat, which is why LED bulbs have largely replaced these lamps.
A is wrong because aluminium melts at only about 660°C. B is wrong because copper, used in household wiring for its low resistance, melts at about 1,085°C. D is wrong because silver is the best electrical conductor but melts at about 962°C and would fail at once.
Exam tip: tungsten for bulb filaments (highest melting point), nichrome for heater coils, tin–lead alloy for fuse wire.
Practice Questions
View allWhich of the following statements about electromagnetic waves, sound waves and water waves is/are correct ? 1. They exhibit reflection 2. They carry energy 3. They exert pressure 4. They can travel in vacuum Select the correct answer using the code given below :
- A.1,2 and 3
- B.2 and 4
- C.1 and 3 only
- D.1 only
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All three kinds of wave reflect, carry energy and exert pressure, but only electromagnetic waves can travel through a vacuum.
Read the full explanation →Which one of the following is NOT the unit of energy?
- A.Joule
- B.Watt-hr
- C.Newton-metre
- D.kg-metre/sec²
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A kilogram-metre per second squared is mass times acceleration, which is force; it is the newton, not a unit of energy.
Read the full explanation →To protect steel and iron from rusting, a thin layer of which one of the following metals is applied?
- A.Magnesium
- B.Zinc
- C.Aluminium
- D.Lead
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Coating iron or steel with a thin layer of zinc is called galvanisation, and it is the most common way to protect them from rusting.
Read the full explanation →In an electric circuit, a wire of resistance 10 Ω is used. If this wire is stretched to a length double of its original value, the current in the circuit would become :
- A.half of its original value.
- B.double of its original value.
- C.one-fourth of its original value.
- D.four times of its original value.
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Stretching the wire to twice its length makes its resistance four times larger, so at the same voltage the current falls to a quarter.
Read the full explanation →Which one of the following scientists mentioned that an electron in an atom could revolve in certain stable orbits without the emission of radiant energy ?
- A.Ernest Rutherford
- B.J.J. Thomson
- C.Niels Bohr
- D.Albert Einstein
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In his 1913 model of the atom, Bohr proposed that electrons move in certain fixed orbits, called stationary states, in which they do not radiate energy.
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