CH 15: Static Electricity

• All metals are made up of tiny particles called atoms, which consist of electrons, protons, and neutrons.
• The number of protons, neutrons, and electrons of every known element can be determined from the periodic table.
• A neutral oxygen atom is made up of 8 protons, 8 electrons, and 8 neutrons.
• The region that consists of protons and neutrons only is called the nucleus.
• All electrons move around the nucleus in no fixed orbits, while neutrons do not carry any charge, protons carry positive charge, and electrons carry negative charge.
• An atom will be positively charged when it loses electrons because it has more protons than electrons, and will be negatively charged when it gains electrons because it has more electrons than protons.
• Like charges repel each other, while unlike charges attract each other.
• An object will have net positive charge if it lacks negative charges, and negative charges if it has excess of negative charges.
• When two charged objects are blocked together, the objects will experience either attractive or repulsive force.
• Electrostatic paint spray gives an evenly coated paint and covers hard to reach areas.
• Electrostatic fertilizer or pesticide spray used in farms sprays fertilizer or pesticide evenly without wastage.
• Electronic factory workers need to wear antistatic gowns, gloves and shoes before entering the factory.
• Handphones are not allowed to be used in petrol stations as they transport petrol or flammable materials.
• Electrostatic precipitators remove smoke and dust particles from exhaust gases before they pass out of emission chimneys to reduce air pollution.
• Electrostatic discharge creates spark which can ignite flame, member materials and cause fire or explosion.
• Anti-static bags are used to store electronic components to protect them from electrostatic charges.
• Photocopiers or laser printers work by charging a document, reflecting it to a charge drum, forming a charged image on the drum, spraying toner particles onto the drum, and fixing the toner particles on the paper.
• Electrical charges cannot be created or destroyed, the charge of an object will change when it loses or gains electrons.
• Discharging is the process of neutralizing a charged object, an object is neutralized when there is no net charge.
• The number of positive charges of protons is equal to the number of negative charges or electrons.
• Charging can be divided into two categories: discharging insulators and discharging conductors.
• Insulators can be discharged by heating over a flame, heat from flame creates charged air particles that neutralize the charged object, water molecules in air can also remove excess charges from an object.
• Conductors can be discharged by earthdam, in a negatively charged object earthling provides a path for excess electrons to flow away from the object, in a positively charged object earthling provides a path for required electrons to flow into the object.
• Charging is the process of causing an object to be charged, an object becomes positively charged when the number of electrons is greater than the number of protons, and becomes negatively charged when the number of electrons is less than the number of protons.
• Charging can be divided into two categories: charging insulators and charging conductors.
• A positively charged insulator is brought near to the neutral metal sphere, causing electrons in the metal sphere to be attracted towards the insulator.
• A positive test charge experiences zero resultant electric force at the x position, indicating that unlike charges attract.
• Examples of insulators are plastic and hair, while examples of conductors are glass and silk.
• The insulator that loses electrons becomes positively charged, while the insulator that gains electrons becomes negatively charged.
• There are two ways of charging by induction: single conductor and double conductors.
• In the double conductor by induction method, two metal spheres a and b are in contact with each other, with a negatively charged insulator placed near sphere a.
• Electrons are less than the number of protons, making an object negatively charged when the number of electrons is more than the number of protons.
• In the single conductor by induction method, a metal sphere is placed on an insulating stand, with an insulating stent used to prevent the sphere from touching the ground.
• The positivity charge is neutralized by earthing the sphere by touching it with finger or connecting it to ground with a piece of wire.
• Conductors can be discharged by the process of induction.
• Sphere a loses electrons, becoming positively charged, while sphere b gains electrons, becoming negatively charged.
• The negative charges in the insulator repel electrons, causing electrons to accumulate in sphere b.
• If two positively charged planes are placed near each other, the electric field will look like this, and if two negatively charged planes are placed near each other, the electric field will look like this.
• Insulators can be charged by friction or rubbing when two insulators are wrapped together, with electrons from one insulator transferred to another.
• For positive charges, electric field lines point outwards, while for negative charges, electric field lines point inwards.