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Electric Energy in Homes – Explanation

Grade 9
Aug 22, 2022

Key Concepts

  • Energy efficiency
  • CFL
  • Halogen bulb
  • Incandescent bulb


Old style light bulb is not very efficient as compared to a compact fluorescent bulb. In this session we are going to learn more about efficiency for a few appliances. We are also going to learn how CFLs are better than other bulbs including listing few other such ways to reduce the energy wastage. 


Energy efficiency: 

Efficiency is the term used to describe how well something does it’s job and how little energy is required to do that job. For example a television uses electrical energy and this electrical energy is converted into light energy, sound energy and heat energy. Out of these energies light and sound enery are the useful energy whereas the heat energy which results in the heating of the appliance is known as the waste energy.  

More is the wastage energy less is the efficiency of the applaince. So, efficiency is defined as the percentage of energy input that is converted to a useful form. 


Knowing how efficient something helps people to decide which device will overally cost less to use. It has no units. 


There are a few ways by which more of the useful energy can be harnessed and it can be made sure that less energy is wasted. A few of the ways are: 

  • Choosing a device properly to meet the minimum efficiency standards.  
  • Improving a home’s overall insulation. 
  • Installing a built-in thermostat with a timer. 
  • Using CFL (Compact fluorescent tubes) at homes for lighting. 
  • Limiting the use of electrical appliances.  
  • Using the electrical resource wisely. 
Energy efficient house 

Energy efficient devices 

Different types of appliances are there. If you want to buy even a bulb you will find so many varieties in it. How to choose the best bulb in such a case? The method is to check how energy efficient it is.  

Let us have a look at a few of the light bulbs. 

  1. Incandescent bulb 
  1. Halogen bulb 
  1. CFL 
  1. Incandescent bulb: 

These bulbs are most used in houses. They have a filament made up of a metal called tungsten. When current flows through it, the filament heats up and becomes so hot that it glows. These bulbs have 5% efficiency. They are cheaper but they do not last longer.  

Incandescent bulb 

  1. Halogen bulb 

They are filled with a high pressure gas containing traces of iodine to preserve the filaments. They operate at very high temperatures thus making the bulb to glow brighter. They do not have very long life.They are 15% efficient. 

 Halogen bulb 

  1. CFL (Compact fluorescent lamp) 

They contain gas in it. When current passes through the vapour, it emits energy that affects the white material on the inside of the glass and cause it to glow. They operate at low temperature and has an efficiency of 20%. They have a very long life  and because of all this reason is very expensive. 


Questions and answers 

Question 1: How efficient is an incandescent light bulb if it uses

7 ×  105 𝟕 ×  𝟏𝟎𝟓 

J to provide

5.4 ×  104𝟓.𝟒 ×  𝟏𝟎𝟒 J of light energy? 


Question 2: A 2000 W electric heater is used for 4 minutes. If it takes

1.5 ×  105 𝟏.𝟓 ×  𝟏𝟎𝟓 

J of energy during this time, what is the efficiency of this heater? 


Question 3: Think of a few ways to increase the efficiency of a washing machine during winters. 


A few ways to increase the efficiency of a washing machine during winters are: 

  1. Air drying the clothes when the weather is suitable.  
  1. Sort loads into heavy, medium, and lightweight items and use dryer on them separately as different weight items will dry separately. 
  1. Do consecutive loads since the dryer will already be active and warm. 
  1. Clean the lint filter weekly. 


  1. Energy efficiency is the percentage of energy input that is converted to a useful form
  • Efficiency = Useful energy out / Total energy in × 100
  1. Useful energy is used by us and is required.
  2. Using proper appliances and using them wisely can make them efficient.
  3. CFL is a better option than other light bulbs.


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