(Solved): Electrical physics Q12: A lightbulb is initially at \( 22^{\circ} \mathrm{C} \) when it is off. The ...

Q12: A lightbulb is initially at \( 22^{\circ} \mathrm{C} \) when it is off. The lightbulb filament consists of a tungsten wire that is \( 0.4 \mathrm{~m} \) long and has a cross-sectional area of \( 5.6 \times 10^{-10} \mathrm{~m}^{2} \). If the lightbulb is connected to a \( 240 \mathrm{~V} \) source then find: (1)- The initial resistance of the lightbulb. (2)- The initial current in the lightbulb. (3)- The final power (operational power) of the lightbulb if it's operational temperature is \( 1400^{\circ} \mathrm{C} \). (The potential difference cross the lightbulb remains the same at \( 240 \mathrm{~V} \) ). Use the followings: \[ \rho \text { Tungsten }\left(22^{\circ} \mathrm{C}\right)=5.6 \times 10^{-8}(\Omega . \mathrm{m}), \alpha_{\text {Tungsten }}=4.5 \times 10^{-3}\left({ }^{\circ} \mathrm{C}^{-1}\right) \] Q13: For the circuit shown find: (1) \( -\mathrm{I}_{1}, \mathrm{I}_{2} \) and \( \mathrm{I}_{3} \) when the switch \( \mathrm{S} \) is open. (2)- \( I_{3} \) and \( \varepsilon \) when the switch \( S \) is closed if \( I_{1}=2 \)