Question

A room has two tube lights, a fan and a TV. Each
tube light draws 40 W, the fan draws 80 W and
the TV draws 60 W. On an average, the tube lights
are kept on for five hours, the fan for 12 hours
and the TV for eight hours every day. The rate for
the electric energy is `3.10 per kWh. The cost of
electricity used in this room in a 30-day month is

Answer 1

The total power two tube lights consume = 40+40

= 80W

Power × hours = Wh

80 × 5 = 400Wh

To convert into kWh, multiply and divide by 1000

= 400Wh × 1000/1000

= 400kWh /1000        (As 1000 = k)

= 0.4kWh

This is the kWh the tube lights consumed per day.

For one month, multiply kWh of one day with 30.

Hence,

kWh of one month = 0.4 × 30

= 12kWh

Therefore, tube lights consume total 12kWh in one month.

Similarly, for the TV and fan.

Watt-hours = 60 ×8

= 480Wh

To convert into kWh, multiply and divide by 1000

kWh = 480Wh × 1000/1000

= 480kWh/1000 (As 1000 = k)

          =0.48kWh

This is the kWh the TV consumed per day.

For one month, multiply kWh of one day with 30.

Hence,

= 0.48 × 30

=14.4kWh

Similarly for fan,

Watt-hours = 80 × 12

=960Wh

To convert into kWh, multiply and divide by 1000

kWh = 960Wh × 1000/1000

= 960kWh/1000 (As 1000 = k)

=0.96kWh

This is the kWh the fan consumed per day.

For one month, multiply kWh of one day with 30.

Hence,

= 0.96 ×30

=28.8kWh

Total kWh consumed by all of them in one month = 28.8+ 12 + 14.4

= 55.5kWh

Electric energy is 3.10 per kWh.

The cost of electricity = 3.10 × 55.5

=172.07

Answer 2

The following is the power consumption formula:

$E=P\times(\frac{t}{1000})$

where $E$ denotes energy in Joules or kilowatt-hours $(kWh)$, $P$ denotes power units in Watt, and t is the amount of time the power or energy was utilised.

1. power consumption by tube lights in a day$=2\times 40W\times5hrs=400Wh$

2. power consumption by the fan during a day$=1\times 80W\times12hrs=960Wh$

3. Power consumption by television in a day$=1\times 60W\times 8hrs=480Wh$

4. Total power consumption in a day$=400+960+480=1840Wh$

5. Power consumption for 30 days$=30\times1840= 55200WH=\left ( \frac{55200}{1000} \right )=55.2KWh$

6. Rate of $1KWH=$ ₹$3.10$

7. Cost of electrical energy used$=55.2\times3.10=$ ₹$171.12$

Hence, the cost of electricity used in this room in a 30-day month is

₹$171.12$.