Static Electricity

  1. The study of static electricity is called electrostatics.
  2. Static electricity is electric charge that is at rest or not moving.
  3. There are two types of static electric charges, i.e. positive charges and negative charges.
  4. Positive charges consist of protons. Protons do not move.
  5. Negative charges consist of electrons. Electron transfer happens when two different materials are rubbed together.

Types of static electric charges and their properties

  1. Charges of the same type (like charges) repel one another.
  2. Charges of different types (unlike charges) attract one another.
  3. The repulsive force and attractive force that exist between electric charges is called electrostatic force.
  4. Electrostatic force on a charged object causes neutral objects to be attracted to it. Examples: bits of paper and hair.

Production of static electric charges

  1. Static electric charges can be produced on a neutral object by rubbing it with a different material like a woollen or silk cloth.
  2. When two different materials are rubbed, electron transfer occurs. One of the material receives electrons while the other loses electrons.
  3. The material that receives electrons becomes negatively charged because it has more electrons than protons.
  4. The material that loses electrons becomes positively charged because it has more protons than electrons.
  5. An object is neutral if the number of positive charges (protons) and negative charges (electrons) is the same.

Detection of electric charges

  1. An electroscope is used to detect small electric charges or static electric charges.
  2. Charged materials can be detected by an electroscope.
  3. Before it is used, the electroscope should be earthed by touching the metal disc with a finger. This is intended to neutralise the electroscope.
  4. When a charged material is brought near the metal disc of the electroscope, its gold leaf will diverge.
  5. When a material that is not charged (neutral) is brought near the metal disc of the electroscope, its gold leaf does not diverge.

Phenomena related to static electric charges in daily life

Friction between two materials produces electric charges. Because of this, electric charges can be produced anywhere:
Occurrence of lightning
  • Clouds acquire electrical charges when water vapour in it rubs with air particles.
  • Lightning can also occur when two groups of clouds of opposing charges come close to one another.
  • Electric charges will jump from one group of clouds to another.
  • Hence, lightning is produced.
Spark plug
  • A spray of sparks is produced when a car engine is started.
  • Electric charges 'jump' across spark space on the plug to produce sparks.
  • These sparks cause fuel to burn to produce energy.
Nylon clothes
  • A crackling sound is heard when we take off our nylon clothes on a dry day.
  • This is because static electric charges are produced when the nylon clothes rub against our body.
Combing hair
  • Dry hair will stand erect or will be attracted towards the comb on a dry day.
  • This is because hair becomes charged when it rubs against the comb.
Electronic lighter
  • Electric charges are produced when an electronic lighter is lit to produce sparks.
  • The sparks will then ignite the gas.

Safety measures relating to static electric charges

Safety measures should be taken in certain situations relating to static electric charges: 
Lightning conductor
  • The roofs of high buildings are usually installed with lightning conductors to protect these buildings from being struck by lightning.
Oil tanker
  • An oil tanker becomes charged with static electricity when it moves because of friction with air particles.
  • Furthermore, the rubber tyres prevent the charges from flowing to the Earth.
  • Because of this, a metal chain is fixed to the bottom of the tanker to direct the charges to the Earth when the metal chain touches the ground.
  • This is important as it prevents sparks from being produced that may cause a fire.
Aeroplane
  • An aeroplane will acquire high electric charges when it rubs against the air as it flies.
  • Aeroplane tyres are specially made to direct electric charges to the Earth when the plane lands.