a)\(R_1//R_2\Rightarrow R_{12}=\dfrac{R_1\cdot R_2}{R_1+R_2}=\dfrac{20\cdot30}{20+30}=12\Omega\)
\(U_1=U_2=U=220V\)
\(I_1=\dfrac{U_1}{R_1}=\dfrac{220}{20}=11A;I_2=\dfrac{U_2}{R_2}=\dfrac{220}{30}=\dfrac{22}{3}A\)
b)Chiều dài dây: \(R=\rho\cdot\dfrac{l}{S}\)
\(\Rightarrow l=\dfrac{R\cdot S}{\rho}=\dfrac{20\cdot0,56\cdot10^{-6}}{2,8\cdot10^{-6}}=4m\)
c)\(R_Đ=\dfrac{U_Đ^2}{P_Đ}=\dfrac{220^2}{60}=\dfrac{2420}{3}\Omega;I_{Đđm}=\dfrac{P_Đ}{U_Đ}=\dfrac{60}{220}=\dfrac{3}{11}A\)
\(R_1//R_2//R_Đ\Rightarrow U_1=U_2=U_Đ=U=220V\)
\(I_Đ=\dfrac{U}{R_Đ}=\dfrac{220}{\dfrac{2420}{3}}=\dfrac{3}{11}A=I_{Đđm}\)
Vậy đèn sáng bình thường.
Công suất đèn: \(P_Đ=\dfrac{U^2}{R_Đ}=\dfrac{220^2}{\dfrac{2420}{3}}=60W\)
