Question

4 electric bulbs of 60 W each is used for 5 hrs in a day and 2 electric fans of 120 W each is used for 8 hrs in a day. Calculate the cost of electric bill at the rate of Rs. 3 per unit.​

Answer 1

Answer:

4 bulb used for 5hrs each day 60×5×4=1200 watt hr

2 fan used for 8 hrs each day 120×2×8=1920 watt hr

so total watt used = 1920+1200 = 3120

3120 watt hour= 3.12 unit

so cost of electric bill per day is 3.12×3 = Rs9.36

per month =Rs 280.8

Answer 2

Answer: Rs. 9.36/day

We are given some electrical instruments with their power and time of their usage in a day.

There are as follows:

4 Electric Bulbs :-

• Power = 60 W
• Usage time = 5 hours a day

2 Electric Fans :-

• Power = 120 W
• Usage time = 8 hours a day

Let's find the electrical energy consumed by the 4 bulbs which is equal to:

⇒ E₁ = 4 × Energy consumed by 1 bulb

⇒ E₁ = 4 × ( Power × Time taken )

⇒ E₁ = 4 ( 60 × 5 )

⇒ E₁ = 4 ( 300 Wh)

But we need the energy consumed in kWh as the rate of electric bill is given per unit which kWh.

Hour is already in Wh, We just need to convert W (Watt) into kW (kiloWatt) by dividing the value by 1000.

⇒ E₁ = 4 (300 / 1000) kWh

⇒ E₁ = 4 × 3/10

⇒ E₁ = 1.2 kWh

Similarly we follow the same procedure with the two electric fans as well, Lets see how,

Energy consumed by the two fans is given by:

⇒ E₂ = 2 × Energy consumed by 1 fan

⇒ E₂ = 2 ( Power × Time taken )

⇒ E₂ = 2 ( 120 × 8 )

Similarly, In this case time is already in Hour and we need to convert Watt into kilowatt by dividing the value by 1000,

⇒ E₂ = 2 (120×8 / 1000)

⇒ E₂ = 2/100 × 12 × 8

⇒ E₂ = 1/50 × 96

⇒ E₂ = 1.92 kWh

Let's find the total energy consumed now, which is given by :-

⇒ E = E₁ + E₂

⇒ E = 1.2 + 1.92

⇒ E = 3.12 kWh

Since, one unit ( 1 kWh ) costs per Rs. 3, hence for 3.12 kWh, It will cost us :-

⇒ Cost = Rate × Units

⇒ Cost = 3 × 3.12

⇒ Cost = 9.36

Electric bill of the electrical instruments in per day is Rs. 9.36