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Electric Current: Sources of Electrical Energy

Grade 9
Aug 22, 2022

Key Concepts

  • Piezoelectric crystal in production of electric current
  • Solar cells in production of electric current
  • Thermocouples in production of electric current
  • Generators in production of electric current


Electricity is a form of energy. It can be converted from one form to another but can neither be created nor destroyed, as per the law of conservation of energy. A few of the sources which are used for the generation of energy are: solar energy, hydro energy, tidal energy, geothermal energy, biomass, fossil fuel and nuclear energy. These energies come from two groups of resources, i.e., renewable resource and non-renewable resource of energy. These resources are used to generate electricity. In this chapter we are going to study about other forms which are used to generate electrical energy.  

sources of energy


These are a few common ways by which energy is harnessed.  

Besides these there are a few other forms of energy in which separation of charges is done to provide electrical energy. A few of them are: 

  1. Piezoelectric crystals 
  1. Solar cells 
  1. Friction 
  1. Thermocouple 
  1. Generators 

Piezoelectric crystals  

‘Piezo’ means pressure or push.

Piezoelectric crystal 

As the name suggests, when crystals, such as quartz, are hammered or squeezed, positive and negative charges are separated on either side of the crystal generating a burst of thousands of volt of electricity. 


Most common crystals used are lead zirconate titanate crystals. Example: barbecue lighter. 

Solar Cell 

A solar cell is made up of photoelectrochemical cell. It is made up of conducting materials such as silicon. 

 solar cells

When light hits the cell, some energy breaks electrons off the surface of the cell. These charges cause electricity to flow. 

Example: solar watch, solar calculator 


When two materials such as hair and comb, glass rod and silk cloth, sealing wax and wool are rubbed together vigorously a charge is generated on both the materials.  


These charges are known as static charge or frictional electricity.

Static charge


As the name suggests there is a couple involved in this.  

Two strips of dissimilar metals of same size are taken and joined together to form a loop. 

One of the metal in the loop is made very hot and the other metal is made very cold. This separates the charges, and a voltage is created. 

Several thermocouple joined together create a large amount of energy.



It works on the principle of electromagnetic induction which was discovered by Michael Faraday in 1831-32. 

An electrical conductor such as a wire is moved in a magnetic field. 

This movement creates a voltage difference between the two ends of wire which causes the charge to flow, thus generating electrical current.


Questions and answers: 

Question 1: Imagine that it is a cold winter day, and you are removing your woolen sweater. As you pull it over your head, you see little sparks and you hear popping and crackling sounds in the sweater. Explain what might be causing the sparks and sounds. 


The charges generated due to rubbing of the woolen sweater against the hair causes the sparks. The discharge of the sparks causes the sound. 

Question 2: Explain why a charged balloon will “stick” to a wooden wall but not to a metal wall. 


Charged balloons would stick to a wood wall but not to a metal wall because the electrons in the metal are free to move about. The charges can flow from the balloon into the metal or from the metal into the balloon, thus, neutralizing the negative charge of the balloon. This is not the case in the wood. 

Question 3:  

Explain why clothes dried in the clothes dryer have more static electricity than those dried on a clothesline. 


Clothes on a clothesline are not touching each other thus, no charge is generated. 

In the case of a dryer since the clothes are continuously rubbing against each other, static electricity is generated. 


  • Electricity is a form of energy
  • The renewable source of generating electricity make use of sun, wind and water and the nonrenewable source of generating electricity makes use of fossil fuels and nuclear energy.
  • Energy can also be created by separating the charges.
  • Piezoelectric crystals – Charge are separated by applying pressure
  • Solar cells – charges are separated when light strikes the photoelectrochemical cell.
  • Friction-charges are generated by rubbing two objects together


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