Write three properties of filament? Don't write search on internet?
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A.Tungsten has the highest melting point of any metal (so it can be heated to high temperatures and incandesces well without melting), high tensile strength (so it remains strong even when drawn into thin wires), low vapor pressure (so it doesn't produce tungsten vapor / dust floating around in its environment) and has a low coefficient of thermal expansion (so that when it's heated and cooled, it doesn't strain its points of connection to the electrodes).
B. Carbon can, in fact, be used as an incandescent light bulb filament. However, since it isn't a metal, it is essentially a brittle substance, and the slightest shock or vibration could knock it loose from its connections with the electrodes.
Early filaments compromised on this -- carbonizing a thin, flexible fibre so that the electricity could flow through the carbon and cause it to incandesce, while the remainder of the substance remained semi-flexible. It wouldn't burn because of the use of a vacuum or inert gas, but shortcomings in vacuum pumps and inert gas purity caused problems with early filament life, as the filaments would burn *very* slowly but eventually enough to break the circuit.
B. Carbon can, in fact, be used as an incandescent light bulb filament. However, since it isn't a metal, it is essentially a brittle substance, and the slightest shock or vibration could knock it loose from its connections with the electrodes.
Early filaments compromised on this -- carbonizing a thin, flexible fibre so that the electricity could flow through the carbon and cause it to incandesce, while the remainder of the substance remained semi-flexible. It wouldn't burn because of the use of a vacuum or inert gas, but shortcomings in vacuum pumps and inert gas purity caused problems with early filament life, as the filaments would burn *very* slowly but eventually enough to break the circuit.
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