Find the resistance of `240 V - 200` watt electric bulb when glowing. If this resistance is `10` times the resistance at `0^(@)C` and the temperature of the glowing filament is `2000^(@)C`, then find the temperature coefficient of resistance of the filament.
Text Solution
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For hot bulb at temperature, `t = 2000^@C`, Resistance, `R_(t) = V^(2)/P = (220)^(2)/200 = 242 Omega` Resistance of bulb at room temperature `R = R_(t)/12 = 242/12 ~~ 12 Omega` Since `R_(t) = R[ 1 + alpha xx (1000 -30)]` `242 = 20[1 + alpha + 1970]` `14.1 = 1 +alpha xx 1970` `alpha = 13.1/1970 = 6.6 xx 10^(-3).^(@)C^(-1)`
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