Definition: Static electricity (or static charge) refers to charges that can be collected and held in one place; the word 'static' means 'not moving.'
Historical Context: Ancient scholars observed that rubbing materials like amber with wool or fur could attract dust.
Observed objects becoming 'charged' (= not neutral).
Daily Examples:
Clothing clinging together after coming out of the dryer.
Hair flying up and separating after combing.
Lightning caused by the buildup and release of static charges.
The shock experienced when touching a metal doorknob after shuffling across a carpet.
Friction and Electron Transfer
Friction: A process where two neutral objects rub against each other and become charged due to electron transfer.
Charging Methods:
Friction
Conduction
Induction
Electron Movement in Solids:
Positive nucleus vibrates (KMT) but remains in place.
Electrons can move.
Charge Imbalance:
Loss of electrons results in an overall positive charge.
Gain of electrons results in an overall negative charge.
Example: A balloon gains electrons when rubbed, becoming negatively charged.
Insulators and Conductors
Insulators: Materials that do not allow charges to move easily.
Electrons removed from one location are not replaced by electrons from another location.
Examples: Glass, plastics, ceramics, dry wood.
Insulators can retain a static charge.
Conductors: Materials that allow electrons to travel and flow freely.
Excess electrons spread evenly.
Examples: Metals, which have at least one free electron that can easily be transferred.
Triboelectric Series
Triboelectric Effect: Materials' tendency to become positively (lose electrons) or negatively (gain electrons) charged.
Triboelectric Series: A chart showing the degree of materials' tendency.
Example: Wool tends to become positive, whereas rubber tends to become negative.
Lightning and Static Charge
Lightning Formation:
Ice particles in a cloud rub against each other, building static charge.
Convection causes the top of the cloud to become positively charged and the bottom negatively charged.
Negative cloud bottoms induce a positive charge on the ground.
When enough negative charges accumulate, electrons flow (discharge) downward to the positively charged ground due to attraction, creating a spark (= lightning).
Van de Graaff Generator and Static Electricity
Working Principle:
A rolling rubber belt loses electrons to a bottom metal comb due to friction.
The positively charged belt takes electrons from the top metal comb, which is attached to the metal dome.
The surface of the dome becomes positively charged.
When you place your hand near the dome, static charge builds up, causing your hair to stand on end.
Electric Force
Definition of Force: In physics, a push or pull.
Electric Force: A push or pull between charged objects; it is an action-at-a-distance force (does not require direct contact).
Coulomb’s Law: States that as the distance between charged objects increases, the electric force decreases.
Unit of Charge: Coulomb (C).
Moving 6.25 \times 10^{18} electrons produces 1 C.
Laws of Static Charge:
Like charges repel.
Opposite charges attract.
Neutrals are attracted to charged objects.
Charging by Conduction and Induction
Charging by Conduction: Charging a neutral object by touching it to a charged object, causing electrons to be transferred.
Charging by Induction: Temporarily charging a neutral object by bringing a charged object close to it.
Electrons do not get transferred but move within due to repulsion.
A neutral object can be permanently charged by discharging the relocated charge elsewhere.
Attracting Neutral Objects and Photocopiers
Attraction of Neutral Objects: Induction explains why neutral objects and charged objects attract each other.
Repelled electrons relocate within the neutral object.
Photocopiers: Utilize the principles of static electricity.
Check Your Understanding - KEY
What is static charge?
Static charge is charge that is held in one place.
Explain how an object containing many negatively charged electrons can be neutral.
Neutral means the number of protons and electrons are the same, so the charges cancel out.
A neutral piece of amber becomes negatively charged when rubbed with fur. What charge would the fur possess after charging the amber?
The fur would be positively charged due to friction – electrons have moved from fur to the amber.
What is the difference between a conductor and an insulator?
Conductors allow electrons to travel freely, while insulators do not let electrons move easily within.
Is lightning a static charge, or is it produced by static charge? Explain your answer.
Lightning is produced by static charge (the buildup of charge in the cloud). Lightning is the spark we see – which is the actual transfer of electrons from a negatively charged object to a positively charged object.
How are lighting and Van de Graaff generator similar?
Both lightning and Van de Graaff generator uses static charge. In both, friction causes charging of an object, and the electrons are then transferred.
Describe the movement of electrons when an object is charged by:
a) Friction b) Conduction c) Induction
Movement of electrons:
a) by friction – two neutral objects rub and becomes oppositely charged when an electron travels from one to another
b) by conduction – electrons from a negatively charged object travels to the neutral object
c) by induction – electrons in a neutral object move within (attract or repel) when a charged object comes close
Explain why a charged balloon will stick to a wooden wall but not to a metal wall.
Metal is a conductor, so the extra electrons from the negatively charged balloon will move away, and thus the balloon will not stick. Meanwhile, wood is an insulator, so the static charge will form (movement of electrons within the wall). The negatively charged balloon will stick to the temporary positively charged wall.