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How to Calculate Energy Consumption

Grade 9
Aug 22, 2022

Key Concepts

  • Electrical Consumption
  • Power Rating
  • Power Consumption


With the increase in advancement in technology the energy consumption is also increasing. As compared to the year 1980, the energy consumption in 2013 is three times. In this section we are going to learn the way to calculate this energy consumption and the power consumption. We will understand the factors which affect power consumption.  

Graph showing energy consumption over years 


Energy consumption: 

Think about how energy is used everyday. You wake up to an alarm clock, take a hot shower, prepare hot milk and have it with toasted bread slices. You listen to music on the phone as you get ready for school. You catch the bus to school. That is the energy used right before you start with the day. So much more energy is used the whole day.  

The energy consumed as per its usage can be divided into different categories such as residential, industrial, commercial and many more. 

The electrical energy consumed by any device per interval of time gives power to the appliance. 



power and energy formula


E is the energy consumed. Its SI unit is Joule. 

P is the power rating. Its SI unit is Watt. 

T is the time taken. Its SI unit is second. 


Power rating: 

You must have seen the picture below or something similar at the back of various appliances. This shows the power rating. Power rating is a quantity that describes the total electrical power required for the normal operation of an electric appliance.  

It is the measurement of the amount of electrical energy an electrical device consumes for every second it is in use. The power rating basically shows the power consumption of a device. 

Power rating 

Power consumption: 

Power consumption is directly related to the voltage applied across the appliance, the current passing through it and the time for which it is used. Power consumption gives the power consumed by an appliance over an interval of time. 


P = power consumption 

V = Voltage of the appliance 

I =  Current flowing through the appliance 

R = Resistance of the appliance 

t = Time period for which the appliance is on 

Question: Which of these has the maximum energy consumption? 

Fig. No. 3 

Answer: Air conditioner 

Fig. No. 4:

Answer  :

Compare the energy consumption of 

  1. A fan with power of 120 W 
  1. A motor with power of 200 W both operating for 10 minutes. Which uses more energy? 



1. Energy consumption is the electrical energy consumed by any device per interval of time that gives the power of the appliance.

c(j) = p(w) x t(s)

P= vit = i2Rt= V2/R x t


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