Electric Charge and Static Electricity

Electric Charge

• Touching an object after walking across a carpet and getting a shock relates to electric charge.
• An atom's center contains protons and neutrons, with electrons moving in a cloud around it.
• Protons and electrons possess electric charge, while neutrons have none.

Positive and Negative Charges

• Two types of electric charge exist: positive and negative.
• Protons are positively charged, and electrons are negatively charged.
• A proton's positive charge equals the amount of negative charge on an electron.
• Atoms are normally electrically neutral due to an equal number of protons and electrons.
• Atoms gain extra electrons and become negatively charged, while atoms that lose electrons become positively charged.

Transferring Charge, Static Electricity, and Conservation

• Electrons' binding tightness varies in atoms and molecules.
• Walking on carpet transfers electrons to shoe soles.
• Shoe soles become negatively charged after gaining electrons, whereas the carpet becomes positively charged.
• Static electricity involves the accumulation of electric charges on an object.
• Static electricity charge balance is disrupted.
• The law of conservation of charge says that charge is not created or destroyed.
• Charge can be transferred, causing objects to become charged.

Charges Exert Forces

• Clothes cling together after being dried because opposite electric charges attract, while like charges repel.
• Clothes tumbling in a dryer can become positively or negatively charged by gaining or losing electrons.
• The strength of electric force relies on charge amounts on objects and distance between them.
• Electric force increases with charge amount and decreases with distance.

Coulomb's Law

• The electric force equation relates charge and separation distance for small particles.
• Coulomb's law equation: F = k*(q1*q2) / (d^2), where k ≈ 9.0 × 10^9 Nm²/C² is Coulomb's constant and 'd' is the distance between the centers of two charges q1 and q2

Electric Fields

• Charged balloons or hair movement shows there's an electric field around every electric charge.
• Electric fields exert force on charges, as shown through arrows indicating positive charge movement.

Comparing Electric and Gravitational Forces

• At the atomic level, electric forces are much stronger than gravitational forces.
• Electric forces in atoms cause chemical bonds.
• Most everyday objects are almost electrically neutral, and not much force is exerted between them.
• However, transferring even small charges can make the electric force noticeable.

Conductors and Insulators

• After walking on carpet, reaching for a doorknob can cause a shock.
• Electrons move from shoe to hand, then to doorknob.
• A conductor allows easy electron movement.
• Metals are the best conductors
• Skin conductivity surpasses shoes.
• An insulator inhibits electron movement.
• Electrons in insulators are held tightly to atoms.
• Plastic, wood, rubber, and glass are good insulators.

Charging by Contact

• Electrons transfer between materials when rubbed, making one object negative and another positive.
• This charge transfer through touching or rubbing is charging by contact.

Charging by Induction

• As a charged object nears a neutral one, electrons in the neutral object move.
• Bringing a negatively charged balloon near a sleeve causes the sleeve's electrons to move away, resulting in a positive charge on the surface.
• Rearranging electrons on a neutral object by a charged object is charging by induction.

Lightning

• Lightning is a large static discharge.
• It is caused by static electricity buildup.
• Charge builds up in thunderclouds.
• Static discharge occurs between clouds and the ground when enough charge builds up.
• Electric charges running through the air collide with atoms and molecules, making them light up.

Thunder

• Lightning produces a bright light and powerful sound waves.
• Thunder is the sound produced by lightning.
• Temperature surrounding lightning can reach 30,000°C.
• The rapid movement of air due to heat produces the sound waves you hear as thunder.

Grounding

• Grounding directs electric charges to Earth's surface.
• Earth absorbs excess charge due to its size.
• Metal lightning rods provide a path for excess charges to reach Earth.

Electroscopes

• An electroscope is a device for detecting electric charge.
• It is a glass flask with a metal rod and leaves.

Charging an Electroscope

• The metal leaves of an electroscope hang down when the rod has no charge.
• When a charged object touches the knob, electrons move down the rod into the leaves.
• Touching the knob with a charged objects causes the leaves to repel each other and spread apart.

Electric Current

• Electric current refers to the net movement of electric charges in one direction.
• Electrons move randomly, but current needs a net flow in one direction.
• Amperes (amps, A) measures electron flow, equivalent to 1 coulomb/second or 6.25x10^18 electrons/second.

Voltage Difference

• Electric force propels charges in one direction.
• Higher voltage goes to lower voltage.
• Voltage difference (voltage/potential difference) fosters charge flow, measured in volts (V).

Alternating Current (AC) versus Direct Current (DC)

• AC, or alternating current is the type of current from household electrical outlets.
• AC alternates direction back and forth per second.
• In the U.S., it is 120 times/second.
• DC, or direct current, is what battery-powered devices use.
• DC maintains a constant direction.
• An AC/DC adapter converts AC in DC to charge batteries.

Resistance

• Flashlights use dry-cell batteries to create current to light the bulb.
• Filaments glow when electrons carrying current flow through them.
• As they move through the filament, they hit the metal atoms, turning electrical energy into heat.
• As a result, the filaments get hot enough to produce radiant energy and glow.
• Resistance is when electric current loses energy moving through a material.
• Electrical energy converts to thermal energy/light when there's resistance present.
• Good conductors have less resistance than insulators.
• Resistence is measured in ohms (Ω).

Ohm's Law

• Ohm's Law is the relationship between voltage difference, current, and resistance: current (in Amperes) = voltage difference (in volts) / resistance (in ohms)
• Ohm's law is used to measure resistance.

Batteries

• Batteries provide voltage difference for constant electric current.
• Positive and negative ends of batteries called terminals.
• Closed path linking terminals allows current flow.

Dry-Cell Batteries

• These batteries have two electrodes, one being a carbon rod and the other a zinc container.
• Electrodes are surrounded by an electrolyte paste that allows charge movement.
• Battery is "dry cell" because the electrolyte is paste, non liquid.

Dry-Cell Creation of Electricity

• Connection of terminals causes zinc reaction with electrolyte.
• Electrons move between zinc and chemicals, causing the carbon rod to become positive and electrons to gather on the negative, marked with +/– signs.
• Voltage difference between terminals enables current to flow in closed circuit.

Electric Circuits

• Electric circuits have a closed path to maintain current flow.
• If taken away one part, there is now a broken ciruit where no current flows and the lightbulb cannot light.

Current versus Electron Flow

• Scientists first marked the direction of current as positive charge movement.
• Scientists then found that electrons, negative charges, actually move through the circuits.
• The electron direction contrasts with the movement of electricity.

Wet-Cell Batteries

• Wet cells have two plates of different metals and a conductive liquid.
• Chemical reactions transfer electrons between plates.
• The liquid conductor makes it a wet cell.
• Several connected wet cells give a larger voltage difference than one alone.

Lead-Acid Batteries

• Most car batteries use these.
• These have six wet cells that are connected.
• Cells include lead/lead dioxide plates.
• In sulfuric acid solution, each cell produces 2-V difference.
• With six cells connected, overall difference is 12V.

Electrical Outlets

• Offer a higher voltage difference than batteries.
• Outlets provide 120 V.
• Some outlets giving 240 V allow operation of large appliances like the oven or clothes dryer.
• Current from outlets and alterniating (AC) and current from batteries is direct (DC).

Series and Parallel Circuits

A circuit has three parts:

• A volage difference (battery or electrical outlet)
• Something that uses the energy and provides resistance (lightbulbs, hair dryers)
• A conductor connecting the parts (wires)

Series Circuits

• Current flows in one loop.
• In this cicuit, the current is the same through every part.

Open Circuits

• This refers to when a circuit breaks.

Parallel Circuits

• Circuits have at least two paths for current to move through.
• Houses are wired with parallel circuits.
• When one path opens, the current can still flow through all other paths.

Household Circuits

• Your house uses many things that need energy.
• The combination of all those things are mostly parallel circuits.

Household Wiring

• Main switch and breaker boxes present.
• Parallel circuits stemming out to outlets, lights, and switches.
• Safety using fuses/breakers

Safety Devices

• Many appliances use a circuit, causing higher currents in wires and therefore heat.
• Circuits should use a fuse or circuit breaker to prevent them from over heating and catching fire with a lot of current running through them.

Fuses

• High current melts the metal and breaks the flow in the circuit.
• Fuses must be replaced.

Circuit Breakers

• High current bends the metal and flips the switch to open the circuit.
• Breakers can be reset.

Electrical Power and Energy

• Electrical energy can be easily changed into other types of energy.
• Electrical power is the rate at which electrical energy is changed.
• An electrical heating element is a device that usually uses the most power.

Calculating Electrical Power

• Elecrical power is based on current x voltage difference
• The base unit for power is the watt, but kilowatts are often used for electrical power One kilowatt equals 1,000 watts

Calculating Electricity

• Electricity companies charge for electrical energy.
• Electricity is typically measured in kilowatt hours (kWh)
• Electrical energy = electrical power x time.

The Cost of Electrical Energy

• To figure out how much it costs to use an appliance, multiply the energy used by the amount it costs per kWh.
• Cost = kWh used x cost per kWh.