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Energy Consumption is the output of a specific amount of energy used. It is also known as power consumption. Thus, power is equivalent to time's labour. It is calculated using the formula,
Energy Consumption Formula: E = P*(t/1000)
Where
E is energy measured in Joules or Kilowatt-hours (kWh),
P is power units in watts, and
t is the period during which the power or energy was consumed.
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Key Terms: Energy, Classification of energy, watts, Joules, power, consumption of energy.
What is Energy?
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The term "energy" is defined as the capacity to do work. It does not represent electrical energy alone but also refers to energy derived from food, heat, and other sources. Both, however, have their formulas. Hence, energy is the usage of power that is supplied. The SI unit of energy, the joule (J), is used to measure energy. Gigajoules per year, kilogrammes of oil equivalent per year (kg/a), and Watts are used to calculate the consumption of energy.
Energy and its types
Derivation of Energy Consumption Formula
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It is known that energy calculation is the number of power units consumed over some time.
Energy = Power x time = P × t
The calculation of power/Energy consumed is usually done in Kilowatt-hour.
Thus to be on the same unit, time is divided by 1000. Thus energy consumed over a period of time is equal to,
E = P × (t/1000)
Energy Consumed can be rewritten as
Since P = V × I
Energy Consumed can be rewritten as
E = (V × I) × t
Also V=I×R by Ohm’s law
E = (I² ×R) × t
Again by Ohm’s law I=V/R
E = (V² / R)×t
Therefore E= P × (t/1000) = (V × I) × t = (I² ×R) × t = ( V² / R) × t = VQ
where
E is energy measured in Joules or Kilowatt-hours (kWh),
P is power units in watts, and
t is the period during which the power or energy was consumed.
I is the current
R is resistance
V is the voltage
Q is point charge in coulomb
Advantages & Disadvantages of Energy Consumption
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The consumption of energy has its own set of pros and cons as follows.
Advantages
- Economic Growth: Improving energy efficiency can reduce individual utility costs, create jobs, and assist in stabilising electricity prices and volatility. Energy consumption for domestic purposes indicates the betterment of the quality of life.
- Utility System Benefits: Energy efficiency can give long-term benefits by lowering overall electricity consumption. Reducing the need to invest in new electricity generating mechanisms and transmission infrastructure.
- Risk Management: Energy efficiency also aids in the diversification of utility resource portfolios and can act as a hedge against the uncertainty associated with shifting fuel costs.
Disadvantages
- It has certain negative effects, particularly on the environment, by depleting the natural resources for energy generation.
- Air pollution- Gaseous by-products and waste disposal from vehicles and power plants degrade the quality of air and increase the atmospheric temperature with the greenhouse effect.
- Water pollution- Waste released by Nuclear power plants cause damage to aquatic life.
- Solid waste disposal like fossil-based energy generation creates major land pollution. Mining such non-renewable resources for energy generation can scar the land, air and water to a huge extent.
Classification of Energy Consumption
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Energy consumption is majorly classified into four categories based on demographic wage.
Worldwide Energy Supply: This refers to the preparation, extraction or generation of energy across the world.
World wide Energy Consumption: This refers to the value of energy used from the total amount of energy produced. If the rate of consumption of energy is more than the rate of production, serious actions need to be taken to improve energy efficiency for the wellness and sustainability of the energy cycle. This factor includes the nature of consumption (domestic, industrial) across the world.
Energy Sources
Domestic Energy Consumption: Unlike Worldwide Energy Consumption, domestic energy consumption states the energy used by households of a particular region. This equals the product of total energy consumed by a household and the total number of households present in the locality. Energy consumption in a household includes electricity, gas, water, and any other energy used to live in it.
Electric Energy Consumption: This specifically refers only to the electric energy consumed exclusively of any other form of energy. This is quantified by the total of all the readings of electric metres present in the domestic and industrial areas.
All of this is to say that energy consumption does not always come from a single source.
Things to Remember
- 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.
Sample Questions
Ques. In a house, there are 5 lamps 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 (30 days)? (3 marks)
Ans.
The lamp's power is 5(25) = 125 Watt,
The length of use per month is 14 hours x 30 = 420 hours.
The refrigerator's power is 200 watts
The length of use is 24 hours x 30 = 720 hours.
Water pump power = 125 watts
Use duration = 8 hours x 30 = 240 hours
Energy=Power x time=P × t
Energy (light) = (125 Watt)(420 hours) = 52,500 Watt jam = 52,5 kiloWatt hours
Energy (refrigerator) = (200 Watt)(720 hours) = 144,000 Watt jam = 144 kiloWatt hours
Energy (water pump) = (125 Watt)(240 hours) = 30,000 Watt jam = 30 kiloWatt hours
Electrical energy used in a month = 52,5 + 144 + 30 = 226,5 kiloWatt hour = 226,5 kWh
Ques. If a 40-watt lamp is turned on for one hour, how many joules of electrical energy has been converted by the lamp? (2 marks)
Ans.
Energy=Power x time=P × t
Since it is a small electrical appliance watt-sec is used instead of kilowatt-hour
1Hr=60x60=3600seconds
Energy = 40 x 3600 = 14,400 joules
Ques. Calculate the heat produced by an electric iron, which has a resistance of 30 ohms and takes a current of 3 amperes when it is switched on for 15 seconds. (2 marks)
Ans.
Energy=Power x time=P × t
Power = I²R by Ohm’s law
=32 ×30= 270 watts
Energy = Power x Time
= 270 x 15= 4050 joules
Ques.Compute the heat generated while transferring 96000 coulomb of charge in one hour through a potential difference of 50 V. (2 marks)
Ans.
Charge = 96000C,time = 1 hr=3600 s
I=Q/t
=96000/3600
=80/3A
E=V×I×t
=50×80/3×3600
=4800000 J
=4.8×10?J
Ques.An electric iron of resistance 20Ω takes a current of 5 A. Calculate the heat developed in 30 s. (2 marks)
Ans.
Here, R = 20 Ω, I= 5 A, t = 3s
Energy Consumed,
E = I² R t
= 52 x 20 x 30 = 15,000 J
= 1.5 x 104 J
Ques. An electric motor takes 5 A from a 220 V line. Determine the power of the motor and the energy consumed in 2h. (2 marks)
Ans.
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
Ques. The 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? (3 marks)
Ans. 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
Ques. 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 of an electric distribution company if one unit is Rs 4. (3 marks)
Ans.
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
=4x480
=Rs.1928
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