Understanding Static Electricity

Static Electricity

• Static electricity is an electric charge that stays on an object's surface instead of flowing away
• Objects become charged when electrons move between them
• Static charges are fixed in one location until a path to escape is provided
• More electrons than protons result in an object with a negative charge
• More protons than electrons result in a positively charged object
• Objects can have positive, negative, or neutral charges

Balloons and Static

• Rubbing a balloon against hair or a sweater causes electrons to transfer, creating a negatively charged balloon
• The buildup of electrons causes static electricity
• The balloon is then attracted to objects with the opposite charge, such as positive charges

Friction and Electron Movement

• Friction transfers electrons between objects, creating static electricity; a process called "charging by friction"
• Rubbing a balloon on hair builds static charges as electrons transfer from hair to balloon
• Materials have different tendencies of losing or gaining electrons
• Electron affinity determines which materials gain or lose electrons when rubbed together, influencing the resulting charge

Laws of Electrical Charges

• Coulomb (1736-1806) was a French physicist with several discoveries relating to electric charges
• Coulomb's Law states that electrostatic force is directly proportional to the product of charges and inversely to the square of the distance between them
• Like charges repel each other
• Opposite charges attract each other

Insulators and Conductors

• Conductors allow electrons to move freely
• Insulators resist the movement of electrons
• Semi-conductors allow some movement of electrons
• Examples of semi-conductors include water, carbon, and the human body
• Metals are generally good electrical conductors
• Insulators are poor conductors

Three Ways of Charging

• There are three methods to charge an object:
  • Charging by friction
  • Charging by conduction/contact/friction
  • Charging by induction (no contact)
• Insulating materials become electrically charged when rubbed together, causing electrons to transfer from one material to another

Charging by Conduction

• Charging by conduction occurs through physical contact
• Electrons flow from a negatively charged object to a neutral object upon contact
• The negatively charged object loses some charge but remains negative
• The neutral object becomes negatively charged
• A positively charged object removes electrons from a neutral object upon contact, resulting in the neutral object with a positive charge

Charging by Induction

• Charging by induction occurs without direct contact
• A charged object near a neutral object causes electron movement
• A negative object repels electrons, while a positive object attracts them
• Induced charge separation creates regions of opposite charges
• Grounding allows electrons to enter or leave the neutral object
• Removing the ground and charged object leaves the neutral object with an opposite charge
• No electrons are transferred directly from the charged object

Homework Checkpoint 10.1

• Electrons orbit outside the nucleus of an atom
• "Static" means stationary or not moving; static electricity remains in one place until discharged
• Rubbing two different materials together causes electrons to transfer, making one object positively charged and the other negatively charged
• Electron affinity describes an atom's tendency to hold onto electrons
• Human hair is more likely to give up electrons than wood
• Steel is more likely to give up electrons than plastic wrap
• Cotton is more likely to give up electrons than silk

Learning Checkpoint

• The law of attraction states that opposite charges attract each other
• The law of repulsion states that like charges repel each other
• A coulomb is a unit of electric charge equivalent to 6.24 × 10^18 electrons
• An electrical insulator is a material that resists electron movement and holds static charge
• Conduction is the movement or transmission of electrons through a substance
• Copper and aluminum are good conductors
• The human body and carbon are fair conductors
• Rubber and plastic are insulators

Diagram of an Atom

• An atom with four protons, five neutrons, and four electrons contains:
  • 4 protons (+) and 5 neutrons (neutral) in the nucleus
  • 4 electrons (-) orbiting outside the nucleus

Friction Questions

• Protons have a positive charge, neutrons are neutral, and electrons have a negative charge
• Friction is the force resisting motion between two surfaces in contact
• When two materials are rubbed together, electrons transfer from one to another
• For example, nylon rubbed with steel causes nylon to lose electrons (becoming positively charged) and steel to gain electrons (becoming negatively charged)
• The statement "A neutral object contains no charge" is false as neutral objects have equal numbers of protons and electrons, cancelling each other out

Laws of Static Electricity

• The laws of static electric charges:
  • Law of Attraction: Opposite charges attract
  • Law of Repulsion: Like charges repel
• Static charges are held on the surface of objects until a path to escape is provided

Static Charge

• A plastic rod with many electrons may not have a static charge if the number of electrons equals the number of protons, keeping the object neutral
• Difference between a conductor and insulator: A conductor allows electron movement, while an insulator resists it
• Copper is a good example of a conductor
• Plastic is a good example of an insulator

Fair Conductor

• A fair conductor allows some electron movement, but not as freely as a conductor
• Tap water from a sink serves as an example of a fair conductor
• Water with dissolved minerals is a fair conductor that can spread electricity and increase danger, it is not suitable for putting out electrical fires
• Two identical objects will not become statically charged when rubbed together, because they have the same electron affinity, meaning no net electron transfer occurs

Pairings

• When rubbed together:
  • Cotton and steel: Cotton (+) and Steel (-)
  • Cotton and silk: Cotton (+) and Silk (-)
  • Human hair and hands: Human hands (+) and Human hair (-)
  • Teflon and wood: Wood (+) and Teflon (-)
  • Glass and plastic wrap: Glass (+) and Plastic wrap (-)

Static Electricity Examples

• Five real-life examples of static electricity:
  • Rubbing a balloon on hair.
  • Removing clothes from a dryer.
  • Getting a shock from touching a doorknob.
  • Lightning during a thunderstorm.
  • Dust clinging to a television screen.

Aluminum Boats

• During a storm, it can be dangerous to fish in an aluminum boat, aluminum is a conductor and water is a fair conductor, and lightning strikes cause electron charges to spread, leading to potentially deadly injuries
• The danger decreases in a lake filled with pure distilled water, because pure water is an insulator and does not conduct electricity

Further Exploration

• How can static electricity be used in everyday applications?
• What are ways to safely discharge static electricity in objects?

Key Concept Review

• Lightning and sparks share similarities, like transfer of electric charge through air and occurring when built-up static charge finds a discharge path
• Lightning is caused by charge separation in clouds
• Objects become negatively charged via the contact method when electrons move from a more electronegative material to the neutral object
• Objects become positively charged via contact when electrons Leave the neutral object when in contact with a positively charged object

Induction

• A substance becomes temporarily charged by induction when a charged object nearby pushes or pulls electrons in the neutral object without direct contact
• Induced charge separation occurs with opposite charges forming on different sides
• The effects disappear when the charged object is removed

Permanent Induction

• Permanent charge by induction involves:
• Bring a charged object near a neutral object.
• Ground the neutral object (allow electrons to enter or leave).
• Remove the ground, then remove the charged object.
• The neutral object is left with a permanent charge opposite to the original charged object

Balloon on a Wall

• A positive balloon sticks to a neutral wall via:
  • Step 1: Bringing near positively charged balloon
  • Step 2: Electrons moving in the wall (induced charge separation) toward balloon
  • Step 3: The now negatively charged wall surface attracting the balloon

Grounding

• Touching a metal shopping cart causes grounding, static charge builds up on the body through walking
• When touching the cart, electrons transfer suddenly, causing a spark
• Lightning strikes cause grounding, clouds build up charge through friction
• When the charge difference is large enough, electrons jump to the ground, releasing energy

Electroscope

• Replacing an electroscope’s metal knob with plastic (an insulator) prevents charge conduction
• An electroscope will not work properly, since charge wouldn’t transfer to the leaves
• The leaves of a charged electroscope move further apart when a rod with the same charge moves near
• The rod pushes more like charges into the leaves which causes the leaves to repel more, moving further apart
• Opposite charges cause the leaves to move together
• The rod attracts opposite charges, pulling some charge away from the leaves

Metal Rods

• Carrying a metal rod prevents a shock when touching a doorknob because the metal gradually conducts charge
• Without the rod, static charge builds up on the person and discharges suddenly

Lightning

• Lightning can be simply explained as being a big spark
• Clouds rub together and get filled with electricity