Question

Answer 1

Điện trở:

\(P=\dfrac{U^2}{R}\Rightarrow R=\dfrac{U^2}{P}=\dfrac{240^2}{4,5\cdot1000}=12,8\Omega\)

Cường độ dòng điện:

\(P=UI\Rightarrow I=\dfrac{P}{U}=\dfrac{4,5\cdot1000}{240}=18,75A\)

Ta có: \(Q_{thu}=mc\Delta t=12,5\cdot4200\cdot80=4200000\left(J\right)\)

Theo PTCBN: \(Q_{thu}=Q_{toa}=A=UIt\)

\(\Rightarrow t=\dfrac{Q_{toa}}{UI}=\dfrac{4200000}{240\cdot18,75}\approx933,3s\)

Answer 2