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How much(in per cent)has a filament diameter decreaseddue to evaporation if themaintancesof the previoustemperature due to evaporation if the maintenance of the previoustemperatur requiredan increasesof the voltageby eta = 1.0 % ? The amount of heattransfereedfromt thefilamentinto surrounding spaceis assumedto be propotional to the filamentsurface area. |
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Answer» Solution :If the WIRE diameter decreases by `sigma` then BYTHE information given `P` = Power input `= (V^(2))/(R)` = beat lostg throgh the SURFACE, `H`. Now, `H prop (1 - sigma)` LIKE the surfacearea and `R prop (1 - sigma)^(2)` So, `(V^(2))/(R_(0))(1 - sigma)^(2) = A (1 - sigma)` or, `V^(2) (1 - sigma)` = constant But `V prop 1 + eta` so `(1 + eta)^(2) (1 - sigma)` = constant = 1 Thus `sigma = 2 eta = 2%` |
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