Question

In a house two 60W electric bulbs are lighted for 4 hours and three

100W bulbs for 5 hours everyday. Calculate the electric energy

consumed in 30 days. Also calculate the cost if the rate is Rs. 3 per

unit.
​

Answer 1

Answer:

The total cost is Rs.67

Explanation:

energy=power.time

so,

total energy per day=(60.4)+(100.5)

=240+500

=740

total energy for 30days= 740.30

=22200watts

1 UNIT=1000WATT

So,

22200watt=22.2units

Therefore,

the total cost =(22.2).3

=66.6

=67rupees.

Answer 2

Case 1 :

• Power, $\sf{P_{1} = 60W$

• Number, $\sf{n_{1} = 2}$

• Time for use everyday  , $\sf{t_{1} = 4h}$

Electrical energy consumed everyday,

                      $\sf{E_{1} = n_{1} \times p_{1} \times t_{1}}\\\sf{= 2 \times 60 \times 4 = 480 Wh = 0.48 kWh}$

⇒ Electrical energy consumed in 30 days  $\sf{ = 30 \times 0.48 = 14.4 kWh}$

Case 2 :

• Power, $\sf{P_{2} = 100 W}$

• Number, $\sf{n_{2} = 3}$

• Time for use everyday , $\sf{t_{2} = 5h }$

 Electrical energy consumed everyday,

            $\sf{E_{2} = n_{2} \times P{2} \times t_{2}}\\ \sf{= 3 \times 100 \times 5 = 1500 = 1.5 kWh}$

⇒ Electrical energy consumed in 30 days =  $\sf{30 \times 1.5 = 45kWh}$

∴ Total electrical energy consumed in 30 days =

$\sf{E_{1} + E_{2} = 14.4 kWh + 45kWh = 59.4 kWh}$

∴ Total cost of electrical energy if the rate is Rs. 3 per unit =

             $\sf{ = Rs.(3 \times 59.4 kWh)}\\\sf{ = Rs. 178.2 kWh}\\\\\sf{\mapsto1 kWh = 1000 Wh}\\\bold{\sf{\mapsto 178.2 kWh = 178200 Wh}}$