Question

4 tube lights of 40 W each and 2 fans of 100 W each are connected to 200 V mains and operate on average for 8 hours a day. If energy costs ₹ 1.50 per kWh, calculate (a) monthly bill (b) minimum fuse rating.

Answer 1

(a) Power of 4 tube lights = \[4 \times 40 = 160\text{ W}\]

Power of 2 fans = \[2 \times 100 = 200\text{ W}\]

∴ Total power of tube lights and fans = \[160 + 200 = 360\text{ W}\]

∴ Energy consumed by tube lights and fans in a day = \[360 \times 8 = 2880\text{ Wh}\]

∴ Energy consumed by tube lights and fans in a month = \[2880 \times 30 = 86400\text{ Wh} = 86.40\text{ kWh}\]

\[\text{Monthly bill} = 86.40\text{ kWh} \times 1.50\frac{\text{₹}}{\text{kWh}}\]

\[\therefore \text{Monthly bill} = \text{₹}129.60\]

(b) Total power of tube lights and fans = \[160 + 200 = 360\text{ W}\]

\[\therefore \text{Minimum fuse rating} = \text{Current drawn} = \frac{\mathrm{P}}{\mathrm{V}}\]

\[= 360 \div 200\]

\[= 1.8\text{ A}\]