Energy Consumed For A Specific Duration Problems|Sub Engineer KSEB

Important points:

Energy Consumption is the output of a specific amount of energy used.
The SI unit of energy is Joule whereas the commercial unit of energy consumed is Kilowatt-hr.
The formula for Energy consumption is E = P × (t/1000).
It can be quantified with E=(V × I) × t=(I² ×R) × t =( V² / R)×t
The total value of energy consumed is the sum of all the energy consumed from various sources.

If a 40-watt lamp is turned on for one hour, how many joules of electrical energy has been converted by the lamp?

One kilowatt hour =

3600000 joules

40×1 = 40 Wh

=(40÷1000)kwh

40×3600= 144000

2. In a house,5 lamps of 25 Watt used 14 hours per day, a 200 Watt refrigerator used 24 hours per day, and a 125 Watt water pump used 8 hours per day. How much electrical energy is used for a month having 30 days

Ans : 226.5 kWh

(5×25×14×30)+(200×24×30)+(125×8×30) watt hrs

226500 watts hr

3. Compute the heat generated while transferring 96000 coulomb of charge in one hour through a potential difference of 50 V

Charge = 96000C,time = 1 hr=3600 s

I=Q/t

=96000/3600

=80/3A

E=V×I×t

=50×80/3×3600

=4800000 J

4. An electric iron of resistance 20? takes a current of 5 A. Calculate the heat developed in 30 s

Here, R = 20 ?, I= 5 A, t = 3s

Energy Consumed,

E = I² R t

= 25 x 20 x 30 = 15,000 J

5. An electric motor takes 5 A from a 220 V line. Determine the power of the motor and the energy consumed in 2h

Current in the motor, I = 5 amp

Potential difference, V = 220 V

Time = 2 hourS

Power of the motor = V × I

= 220 × 5

1100 watt or 1.1. kWh

Energy = power × time

= 1.1 kWh × 2 h.

= 2.2 kWh

6. An electric bulb draws a current of 8A and works on 250 volts on an average of 8 hours a day to find the power consumed by the bulb and find the cost if one unit is Rs 4.

I = 8 A

V = 250 V

t = 8 h

Power consumed = V x I

= 250 V x 8 A

= 2000 W

= 2000/1000

= 2 kW

Assuming the time period of calculation as one month

Electrical energy, E = P x t

= 2 kW x 8 h x 30 days

= 480 kWh

Thus, the cost of electricity for 1 month = Energy Cost per unit x 480 kWh

=4×480

=Rs.1928

7. an electric heater is rated at 2-kilowatt electrical energy and costs 4 rupees per kilowatt-hour. What is the cost of using the heater for 3 hours?

The electric heater rating is 2kW

That is

Power of electric heater (P) = 2 kW

Time for which the cost is to be calculated (t) = 3 hours

Thus, the total electrical energy consumed (E),

E = P x t

= 2kW x 3 h

= 6 kWh

Cost of 1 unit = Rs. 4

Thus,

Cost of electricity = 6kWh x 4 = Rs. 24

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