Static Electricity
- Static electricity is the imbalance of electric charge on a surface of a material.
- The imbalance of electric charge occurs because materials can gain or lose electrons.
- Materials can gain or lose electrons due to friction when two material are rubbed against each other.
- The material that gains electrons becomes negatively charged, and the material that loses electrons becomes positively charged.
For example, when polythene rod is rubbed with dry cloth, electrons will be transferred from cloth to the rod. Cloth will become positively charged while the rod will become negatively charged.
Electrostatic Force
- There is electrostatic force between two charged materials.
- Two like charges will repel each other, and two unlike charges will attract each other.
If we go back to the example of rubbing the polythene rod and dry cloth, will these two materials attract or repel each other?
→ They will attract each other because they have unlike charges.- A fuel tanker can become charged while it is moving due to friction and subsequent transfer of electrons.
- Pumping fuel from an electrically-charged tanker can be dangerous because....
- When the charge builds up in the fuel tanker, the potential difference between the tanker and the ground will also increase.
- With a large potential difference, the charges may escape to the ground as a spark while pumping fuel.
- This spark could cause an explosion or ignite a fire.
- Connecting an earth wire to the tanker before pumping fuel can reduce potential dangers of charge build-up.
- The charge can move through the wire, therefore discharging the tanker.
- No more potential difference remains between the tanker and the ground, so it is unlikely that a spark will occur while pumping fuel into the tanker.
Photocopier
- The plate is positively charged.
- When light is shone onto the paper and the white part of the paper reflects the light onto the plate, the electric charge leaks away. The positive charge is only left where there is an image of the original document.
- Negatively charged toner particles are attracted to the positive part of the plate.
- When a strongly positive charged paper is placed onto the plate, the paper attracts the toner particles.
Inkjet Printer
- Ink droplets become charged as they leave the ink nozzle.
- Ink droplets will deflect as they pass through electrically charged plates.
- By changing the charge of the plates, the direction of ink droplets can be controlled.