Electricity 6667

A light bulb with power consumption P = 70 W. It is connected to a mains voltage of 230 V. How big is the electric current that flows through it? How much electricity in kWh will it use if it is on for 9 hours 30 minutes?

Correct answer:

W =  0.665 kWh
I =  0.3043 A

Step-by-step explanation:

$$\begin{gathered} P=70\text{W} \\ U=230\text{V} \\ t=9+\frac{30}{60}=\frac{9\cdot 60}{60}+\frac{30}{60}=\frac{540}{60}+\frac{30}{60}=\frac{540+30}{60}=\frac{570}{60}=\frac{19}{2}=9.5\text{h} \\ W=P\cdot t/1000=70\cdot \frac{19}{2}/1000=\frac{133}{200}\text{kWh}=0.665\text{kWh} \end{gathered}$$

$$\begin{gathered} P=UI \\ I=P/U=70/230=0.3043\text{A} \end{gathered}$$

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