11. A 100-W incandescent light bulb has a cylindrical tungsten filament 30.0 cm long, 0.40 mm in diameter, and with an emissivity of 0.26. (a) What is the temperature of the filament

Respuesta :

Answer:

 T = 556K

Explanation:

For this exercise let's use Stefan's law

        P = σ A e T⁴

where the stafan-Boltzmann constant is 5,670 10⁻⁸ W / m² K⁴.

In this case the area of ​​a circular cylinder is

        A = π r²

the radius is

         r = d / 2 = 0.150 m

        A = π (0,150)²

        A = 7.0685 10⁻² m²

let's clear

         T⁴ = P /σ A e

         T⁴ = 100 / (5.670 10⁻⁸   7.0685 10⁻²  0.26)

         T⁴ = 9.5966 10¹⁰ = 959.66 10⁸

         T = 5.56 102 K

         T = 556K

The temperature of the filament is 366.3 K

Using the equation for radiated power, P

P = σεAT⁴ where σ = Stefan-Boltzmann constant = 5.67 × 10⁻⁸ W/m²K⁴, ε = emissivity = 0.26, A = area of cylindrical tungsten filament = πDh (since it radiates through its sides)where D = diameter of tungsten filament = 0.40 mm = 0.4 × 10⁻³ m and h = length of tungsten filament = 30.0 cm = 0.3 m and T = temperature of tungsten filament.

Since we require the temperature of the filament, making T subject of the formula, we have

T = ⁴√(P/σεA)

T = ⁴√(P/σεπDh)

Since P = 100 W, substituting the values of the variables into the equation, we have

T = ⁴√(P/σεπDh)

T = ⁴√(100 W/5.67 × 10⁻⁸ W/m²K⁴× 0.26 × π× 0.4 × 10⁻³ m × 0.3 m)

T = ⁴√(100 W/0.5558 W/K⁴ × 10⁻⁸)

T = ⁴√179.93 × 10⁸ K⁴)

T = 3.663 × 10² K

T = 366.3 K

So, the temperature of the filament is 366.3 K

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