Electricity - grade 9

current

the continuous flow of electricity in a closed pathway

static electricity

build up of electric charge on an object because it is not given a path to escape

friction

rubbing together two materials causes electrons to transfer

what are the resulting charges of friction?

1 object positive, 1 object negative

what are the original charges of an object before friction?

they are both neutral

electrostatic series

a list of materials arrange in order according to their tendency to gain electrons

law of electric charges

• like charges repel

• opposite charges attract

• 1 charged and 1 neutral object attract

how is spray painting an application of charging by friction?

friction inside the nozzle causes paint to be negative and the object being painted is either neutral or positively charged so they attract each other

how are dryer sheets an application of charging by friction?

clothes rub together inside the dryer and stick together (called static cling), dryer sheets prevent this by absorbing the negative charge

conduction

• 2 objects have different charges

• objects make contact

• electrons transfer until they have the same net charge

conductor

an object that allows electrons to flow easily

insulator

materials that hold onto their electrons

why is distilled water an insulator?

distilled water does not have any minerals in it, which is what allows normal water to be a conductor

grounding

transferring extra charge (+/-) to an infinite reservoir so the object can be neutral

• grounding can cause an object to loose or gain electrons depending on the situation

• it does not matter how many electrons are given to the reservoir because it’ll be spread over a big area

infinite reservoir

a large neutral object

infinite reservoir examples

humans, the earth

pithball electroscope

a metal ball that will move away/towards an object to indicate the presence of a charge without touching it

metal leaf electroscope

an apparatus with metal leaves that will either repel or attract to indicate that a charge is present without touching the object

induction

• 1 neutral, 1 charged object

• charged object goes near neutral object to induce a temporary charge separation

  • a permanent charge can be created via grounding

how is lightening related to induction

• water droplets rub against each other inside of clouds and become charged

  • negative drops collect at the bottom of the cloud

• negative drops repel electrons on the earths surface

  • causes a temporary charge separation on the earths surface making the surface positively charged

• excess electrons in the clouds take the path of least resistance to get to the earths surface

  • this creates a permanent negative charge on the earths surface

net -1

if an object with a net charge of -3 and an object with a +1 net charge touches, what will be the new net charge?

by grounding (in this case it’ll take away 4 electrons)

how can you make an object with a net charge of -4 neutral?

the electrons will repel the object and temporarily move into the leaves (until the object is taken away) causing them to repel each other

if a negative rod is put near a neutral metal leaf electroscope what will happen?

electrons would be take away to make the leaves neutral. once the grounder is taken away the leaves will repel each other because they’re now both positive

if you were to ground a negative metal leaf electroscope what will happen?

hydroelectricity

energy created by water moving a turbine

pros and cons of hydroelectricity

pro: safe for the environment

con: costly to build dam

direct current

a load gets energy directly from the source

alternating current

a load gets energy from a generating station

What are the 3 things you must consider when choosing an energy source?

Social, environmental, and economic effects

pros and cons of fossil fuels

pro: creates jobs, meets energy demands

con: contributing to global warming, stopping this method would cause people to loose jobs

pros and cons of biomass energy

pro: a renewable source of energy if properly managed

con: if incorrectly managed it will have the same effect as fossil fuels

nuclear energy

pro: creates jobs and lots of energy

con: produces radioactive waste

pros and cons of geothermal energy

pro: renewable

con: hard to harness

pros and cons for solar energy

pro: easy to harness

con: expensive to set up solar panels

pros and cons of wind energy

pro: creates jobs, wind is found everywhere

con: hard to find spot with consistent high winds

3 main components of a circuit

source, load, conductor

series circuit

one pathway for electricity to flow

parallel circuit

multiple pathways for electricity to flow

short circuit

this causes damage to the circuit and could start a fire, this happens when there isn’t a load to drop off energy to in a circuit

fuse

thin piece of metal that breaks when current exceeds safe rate. This prevents short circuiting

voltage

pressure given to current to push it along the circuit

resistance

the force opposing the flow of electrons

4 factors that influence resistance

thickness of wire

length of wire

temperature

material

ohm’s law

mathematical representation of the relationship between voltage, current, and resistance

how do you find voltage?

V=IxR

how do you find resistance?

R=V/I

how do you find current?

I=V/R

series law

Vt= v1 + v2

It= I1 = I2

Rt= R1 + R2

parallel laws

Vt= V1 = V2

It= I1 + I2

1/Rt= 1/R1 + 1/R2