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24 March, 18:23

The filament of a certain lamp has a resistance that increases linearly with temperature. When a constant voltage is switched on, the initial current decreases until the filament reaches its steady-state temperature. The temperature coefficient of resistivity of the filament is 43 times 10^-3 K^-1. The final current through the filament is one - eighth the initial current. What is the change in temperature of the filament?

a. 30100 K

b. 378 K

c. 1627 K

d. 814 K

e. 1162 K

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  1. 24 March, 18:41
    0
    162.8 K

    Explanation:

    initial current = io

    final current, i = io/8

    Let the potential difference is V.

    coefficient of resistivity, α = 43 x 10^-3 / K

    Let the resistance is R and the final resistance is Ro.

    The resistance varies with temperature

    R = Ro (1 + α ΔT)

    V/i = V/io (1 + α ΔT)

    8 = 1 + 43 x 10^-3 x ΔT

    7 = 43 x 10^-3 x ΔT

    ΔT = 162.8 K

    Thus, the rise in temperature is 162.8 K.
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