some flashcards lol electricity

Static Charges

electricity - a form of energy that results from the interaction of charged particles (ie. electrons and protons)

GEN LEP (gain electron = negative, lose electron = positive)

the overall charge that an object has is represented using positive (+) and negative (-) charges

objects with the same charge repels

2 objects meet, electrons are transferred from one object to the other

⇒ one will have an overall negative charge, the other will have an overall positive charge

• the new overall charge (static electricity/charge) will remain on the surface of the object until it has a way to leave

  • static electricity/charge as the charges are stationary on the surface of the object

2 neutral objects of different materials meet ⇒ both objects become charged

electrons need a conductor path (ie. copper wire, water, air) to move

static charges build up as different materials rub together, producing a net static charge

• one material will have a stronger attraction to electrons, pulling the electrons from the other material

• both materials become charged due to an excess/shortage of electrons

ability to hold on to electrons from weak to strong

1. dry human hands

2. glass

3. human hair

4. nylon

5. wool

6. cat fur

7. silk

8. cotton

9. lucite (a clear plastic)

10. rubber balloon

11. polyester

12. foam

13. grocery bags (low density polyethylene)

14. ebonite (a hard form of rubber)

15. plastic wrap

electroscopes detect charges

• pith ball electroscope

  • insulating ball is suspended by a thread

  • charged object near the neutral pith ball will make it move towards the charged object

• metal-leaf electroscope

  • 2 thin metal pieces (leaves) suspended from a metal rod which is attached a top plate or metal knob

  • charge transferred to the plate/knob travels to the leaves ⇒ greater the charge, greater the separation between the leaves

insulators - non-metal materials in which electrons cannot move easily from one atom to another ⇒ low electrical conductivity

conductors - metals and other materials in which electrons can move easily between atoms

semiconductors - materials in which electrons can move fairly well between atoms

water

• pure (distilled) water is an insulator (neutral charge)

  • lacks ions ⇒ electricity has no way of flowing through

• plain (ie. tap) water is a conductor

  • impurities and mineral ions in the water carry a charge ⇒ electricity can flow through the water

  • dangerous to have electronics operating around water

grounding - the process of connecting a charged object to Earth’s surface

• gives positively charged objects electrons, removes electrons from negatively charged objects

• Earth and humans are good grounders

• protects electrical equipment from static charges by reducing buildup of charges (prevents sparks)

symbol for a ground (indicates a material that can discharge a conductor)

ebonite

• easily accepts electrons 

• when rubbed on fur ⇒ gains negative charge

glass

• easily gives away electrons

• when rubbed with silk/plastic ⇒ positive charge

charging by contact - when electrons transfer from the charged object to the neutral object that it touches (neutral object gets same charge as the charged object)

induction - movement of electrons within a substance caused by a nearby charged object, without direct contact between the substance and the object

• negatively charged balloon induces a positive charge on the wall’s surface without touching the wall (negative charge on wall is repelled by the balloon)

charging by induction - use the charged object to induce a charge in a neutral object and then ground the charged object so it retains the charge

electrical discharge - electric charges being transferred very quickly (ie. sparks)

lightning

• very large electrical discharge caused by induction

• (a) charged area (usually negative) builds at the base of the cloud

• (b) temporary positive area on the ground through induction

• (c) path of charged particles forms when enough charge has built up

• (d) cloud discharges its excess electrons along the temporary path to the ground (the air (insulator) cannot keep the charges separated from the cloud and ground anymore) ⇒ spark (lightning)

Current Electricity

current electricity - the continuous flow of electrons in a circuit through a conductor

• operation of electrical devices requires an energy source and a complete path to flow through ⇒ steady flow of electrons

static electricity - the electric charge that builds up on the surface of an object

conventional current - believed by scientists that electrons moved from positive to negative (in reality, electrons move from negative to positive)

• a (+) → b (+) → c (-) → d (-)

circuit - the path that electrons flow through

• every circuit must have an energy source, conductor and load

  • load - something that converts electrical energy to another form of energy (ie. air conditioner)

• every circuit needs potential energy

  • potential energy - the stored energy of an object

    • the greater the height from the ground, the more potential energy

electric current - a measure of the amount of electric charge that passes by a point in an electrical circuit each second

• direct current (DC) - current that flows only in one direction

  • ie. current that has a battery

• alternating current (AC) - current that flows back and forth at regular intervals

  • ie. current that comes from generators to power homes

switch - a device that turns the electricity on or off by closing or opening the switch

electrochemical cell - a package of chemicals that converts chemical energy to electrical energy

• includes an electrolyte and two electrodes

  • electrolyte - liquid/paste that conducts electricity because it contains chemicals that forms ions

  • electrodes - metal strips that react with the electrolyte

• if contains liquid electrolyte ⇒ wet cell

• if contains paste electrolyte ⇒ dry cell

  • electrode in a dry cell can be called a terminal (end points in a cell or battery where we make a connection)

• fuel cell - electrochemical cell that generates electricity directly from a chemical reaction with a fuel (ie. hydrogen)

  • electricity is produced ⇒ more fuel added ⇒ cell never runs out

battery - combination of electrochemical cell

• each battery has a positive end a negative end

potential difference - the difference of potential energy between two points in a circuit (aka. voltage)

resistance - degree to which a substance opposes the flow of electric current through it

• to resist flow, the substance converts electrical energy into other forms of energy such as heat

• affects electrical current

  • for any given potential difference, current decreases if you add resistance

resistors - any material that can slow current flow

• can control potential energy difference

• in a circuit, electrons have a higher potential difference as they enter a resistor than when they leave the resistor as they use some energy in passing through the resistor

• wire-wound resistor - wire made of heat-resistant metal wrapped around an insulating core

  • longer and thinner the wire ⇒ higher resistance

• carbon-composition resistors - made of carbon mixed with other materials that is moulded into a cylinder with a wire at each end

  • cheaper than wire-wound resistors but less precise

• ie. filament in light bulbs

voltmeter - device used to measure the potential energy difference (voltage) of a load

• unit: volt (V)

ammeter - device that measures the amount of charge moving past a point every second (current)

• unit: ampere (A)

ohmmeter - device used to measure resistance

• unit: ohms (Ω)

Series and Parallel Circuits

circuit diagram - simple drawing using special symbols that show the components and connections in a circuit

series circuit - electric circuit where the components are arranged one after another in series

• only one path

• adding additional light bulbs to a series circuit ⇒ they get dimmer

• add resistors ⇒ increase the overall resistance in the circuit

series circuit - electric circuit where the electrons have more than one path

• pathway gets disrupted ⇒ no disruption in the other pathways

• adding resistors ⇒ no change in the resistance of the other pathways, decreases the overall resistance in a circuit

• potential difference (voltage) = same on each load

voltage = current * resistance = ohm’s law

G: given (what are you given in the question)

R: required (what do you need to find)

A: analysis (what formulas are you going to use)

S: solution (use the formula to solve)

P: paraphrase (therefore, …)