electricity unit test

current electricity

electricity that flows through a conducting substance

non-ohmic

doesn’t follow ohm’s law

transformer

an electrical device that transfers energy between two or more circuits using electromagnetic induction

transforms voltage up and down

alternating current

electric current moves back and forth

direct current

flow of electric charge in one direction

ammeter and voltmeter where in circuit is it placed

ammeter is always in series

voltmeter is always in parallel

fuel cell

combines hydrogen gas with oxygen from the air which makes energy and heat and water

secondary cell battery

rechargeable

electric current is passed in the opposite direction through the cell, reversing chemical processes, which restores the battery

primary cell

one use battery

wet cell battery

contains electrolyte that is liquid

usually is sulfuric acid which is corrosive

dry cell battery

contains electrolyte that is a paste

first was the zinc-carbon cell by carl gassner

alkaline cell - more expensive but longer lifespan

electrolyte

a substance that conducts electric current via the movement of ions, rather than electrons

electrode

an electrical conductor used to make contact with a nonmetallic part of a circuit

van de graaf generator

an electrostatic machine that uses a moving belt to accumulate high-voltage static electricity on a hollow metal dome

when you put your hand on it your hair stands up

electric field

a property of space around a charged object where the effect of its charge can be felt by other objects

is water a conductor

pure H2O is a good insulator

water from faucet (unpure) is a good conductor

semiconductor

non-metal where electricity can flow

3 requirements for electricity to be able to move

an amount/volume or current of electricity, a force or potential energy to move electricity, and a pathway made of conductive materials. resistance might be created by a pathway

current

I, refers to the rate of movement or flow of electrons in a circuit, measured in amperes or amps (A). if the current measured has zero A, that means there is no electricity.

potential difference

V, is the force or energy that moves the elctrons through a circuit, measured in voltage or volts (V). voltage is the amount of potential energy (in joules/J) that the elctrons have to move with in the circuit.

resistance

R, the movement of electrons may be hindered by the conducting materials or devices that the circuit is made of. the higher the resistance the harder it is for electricity to move within the circuit

circuit

a controlled pathway for electricity to flow through

2 types of circuits

open circuit - path of electrical current is interrupted and unable to flow

closed circuit - path of electrical current is not interrupted and able to flow

series circuit

electrons only have one path to follow

all electrical devices are connected along the same path

each load shares the energy

if one load is turned off, all loads along the circuit will turn off

adding more loads decreases the electrical pressure to each load

parallel circuit

electrons have multiple paths to follow

each electrical device has its own path

each load does not share the energy

if one load is turned off, the other loads in parallel will still work

current in series vs parallel circuits

series - electric current is the same at all points

parallel - the current has multiple paths; total current is equal to the sum of the currents in the circuit

voltage in series vs parallel circuits

series - the total voltage of the circuit is the sum of the voltage used at each load

parallel - the electrical potential across the circuit is the same

ohm’s law

Georg Ohm measured the current in a circuit while varying the potential difference - discovered that the ratio between potential difference and current was constant

called it resistance

factors that can influence resistance

type of material, cross-sectional area (thinner material = higher resistance), length (longer wire = more resistance), temperature (higher temp = more resistance)

ohm’s law formula

R=V/I

2 power formulas

P=E/t

P=IV

efficiency formula

% Eff = (useful energy/total energy) x 100

potential difference formula

V=E/Q

current formula

I=Q/T

electricity

a form of energy associated with the presence and movements of electrical charges

current electricity

the flow of electric charge through a substance that conducts electricity, such as copper wire

static electricity

electric charge stays in one place and does not move

what happens when objects are charged by friction

one material has a stronger attraction to electrons than the other material, and therefore it pulls electrons off the material that has a the weaker attraction - both materials become charged

movement of charges

most substances are neutral - equal number of protons and electrons

materials that have lost electrons become positive

materials that have gained electrons become negative

charges are created by the movement of electrons

protons never move.

the electrostatic series

when materials are rubbed together, some are more likely to attract electrons and others are more likely to lose electrons

basically is a list of materials that have been arranged based on their ability to hold onto electrons

insulator

materials in which electrons can’t move easily from one atom to another

hold onto their electrons tightly

ex. rubber, glass, diamond, plastic, wood

conductors

materials in which electrons can mmove easily between atoms

materials hold on to their electrons loosely

ex. gold, steel, lemon juice, silver, seawater, copper

is air a conductor or insulator?

air is nomally a poor conductor

wet air is a fair conductor

air is made of particles that can become ionized (form charged particles), which can create a path for an electrical discharge to move through it

ionization can occur by friction between moving air molecules, especially in stroms

sparks occur when an electrical discharge of excess electrons jump from one object to another

law of electric charges

like charges repel, opposite charges attract, charged objects can attract neutral ones

charging by friction

a method of generating static electricity that involves rubbing two neutral materials together, causing electrons to transfer from one material to the other

charging by contact

involves touching a charged object to a neutral object and allowing the electrons to transfer and redistribute

as a result, both objects share the same type of charge

charging by induction with grounding

induction is the process by which an object with an electric charge is able to create a tempoary charge in a neaby object without touching it

to give a neutral object a more permanent charge, the neutral object has to be grounded

grounding requires a counducting pathway - you can use a + material to make the electroscope - charged and vice versa

potential difference

V, volts (V)

current

I, amps (A)

resistance

R, ohm (Ω)

charge

Q, coulomb (C)

time

t, seconds (s), minutes (min), hours (h)

power

P, watts (W)

energy

E, joules (J)

efficiency

% Eff, %

positive terminal

the electrode on a power source with higher electrical potential

negative terminal

the source of electrons in a direct current circuit marked with a minus sign and usually black, representing the point of lowest electrical potential

resistor

a device used in an electric circuit to decrease te current through a component by a specific amount

load

a resistor or any other device that transforms electrical energy into heat, motion, sound, or light

how does lightning occur

air currents in the storm cloud cause charge separation. the top of the cloud becomes positively charged and the bottom becomes negatively charged

negative charges on the bottom of the cloud induce a positive charge on the ground below the cloud by repelling negatuve charges in the ground

when the bottom of the cloud has accumulated enough negative charges, the attraction of the positive charges below causes electrons in the bottom of the cloud to move toward the ground

when the electrons get close to the ground, they attract positive ions that surge upward, completing the connection between the cloud and the ground - this is lightning

lighting rod and its functions

a metal sphere or point that is attached to the highest part of a building and connected to the ground

functions: to reduce the likelihood of a lightning strike, and if a strike occurs, to conduct the charge safely to the ground

power

the rate at which devices use electrical energy, measured in watts or kilowatts

efficiency

the ratio of how much energy a device uses compared to the total enegy provided by the source

non-renewable resource

a natural resource that cannot be regenerated at a scale comparable to its consumption - can’t be replaced in a lifetime

renewable resource

can be replenished in a short period of time

three types of fossil fuels

coal, oil, gas, which provide 66% of the worlds electrical power and 95% of the worlds total energy demand

solar cells

aka photovoltaic cells - they convert light to electricity

sustainability

taking what we need to live now without jeopardizing potential for people in the future to meet their needs

nuclear power

using uranium metal (mined)

around 11% of the worlds energy

nuclear fusion → heat → heated water → steam turns turbine → turbine turns generator → electrical power

produces huge amounts of energy from small amount of uranium without pollution

non-renewable

pros: costs about same as coal, doesn’t contribute to greenhouse effect, produces less waste, produces large amounts of energy from small amounts

cons: dangerous, the waste has to be sealed and buried forever, startup cost is huge, people don’t want to live near nuclear plants

solar power

solar cells aka photovoltaic cells convert light to electricity

renewable

pros: free, needs no fuel, produces no waste or pollution

cons: only get energy during day, expensive to built solar stations, can be unreliable, takes up land