ELECTROSTATICS
- Electrostatics is the study of static electric charges.
- Each atom has negatively charged electrons that orbit round a nucleus.
- A nucleus is made up of
- positively charged particles called protons
- neutral particles called neutrons
- In an uncharged atom,the number of electrons is equal to the number of protons.
- If the atom gains electrons, it becomes negatively charged.
- If the atom loses electrons, it becomes positively charged.
- We can charge certain materials by rubbing them against each other.
- Some electrons from the surface atoms of one material will be transferred to the other material.
- Charge cannot be created or destroyed during friction. It can only be transferred from one object to another.
- Table below shows the charges produced on some materials during friction.
- The force between two charged objects brought close together is called electrostatic force.
- Like charges always repel each other. Unlike charges always attract each other.
Electroscope
- An electroscope is a device used to
- detect charges
- test the kind of charge
- Figure below shows the structure of a typical electroscope.
Detection of Charges
- In an uncharged electroscope,the gold leaf is close to the brass plate. It is said to be in a collapsed state.
- The brass cap, brass rod, brass plate and the gold leaf are electrically neutral. This means that there is no excess charge.
- When a charged object, for example a positively charged glass rod, is placed near the brass cap, free electrons from the brass and gold parts of the electroscope are attracted to the brass cap.
- This results in the brass plate and gold leaf to be positively charged.
- Being positively charged, the gold leaf will diverge since like positive charges repel each other.
- Hence, we can conclude that the glass rod is charged.
Everyday Phenomena Related to Static Electrical Charges
Spray painting
- In car production, electrostatic spray painting is frequently used.
- The car's body and the spray nozzle are given opposite charges.
- The paint can be applied uniformly throughout the car.
Lightning
- Usually, flashes of lightning can be seen before and during a thunderstorm.
- This is caused by the large amount of electrical charges built up in the thunderclouds.
- The thunderclouds are charged due to the friction between water molecules in them and the surrounding air molecules.
- When the charge on the thunderclouds gets large enough, it ionizes the air.
- The ionized air creates a conducting path for the large amount of charge to discharge in the form of lightning to the nearest or sharpest object on the ground.
Fires and explosions
- Too much electric charges produced by friction may cause fires and explosions.
- For example, an aeroplane during a flight accumulates electric charges due to friction with the air molecules.
- An oil tanker becomes charged by friction with air when it moves.
Combing hair
Combing hair on a dry day produce charges. Hair becomes charged and will be attracted to the charged comb.
Safety Measures Taken to Deal with Static Electricity
- During a thunderstorm, do not swim in the open sea or swimming pool, play in an open field or at the beach, or take shelter under a tree.
- Soldiers who build trenches on mountainous areas must not use zinc sheets as shelter from thunderstorms.
- Use lightning conductors on tall buildings to prevent damages caused by lightning.The conductor becomes a discharge path for the electrons to flow from the top of the building down to earth.
- Use slightly conductive rubber for tyres of an aircraft to allow excess electrons to discharge harmlessly during landing.
- A metal chain hanging from the back of the oil tanker allows charges to flow to the ground.
