# Physics 7 Study Guide- Magnetism and Electricity Physical Science

What is a solenoid?
By looping wire, magnetic fields of the wire are layered, creating a strong magnetic field within the “loops”
magnetic field produced by a current
can be turned on or off- turn current on or off
have its direction reversed- reverse current direction
have its strength changed- wires bent into loop inside wire, bunches up magnetic field lines, two loops makes it twice as greater: more loops or coils, stronger magnetic field

A coil of wire with a current: two ends act like magnetic poles
north and south poles change with direction of current

What does a motor do and briefly describe how it works?
Magnets cause a wire with electricity to spin
transforms electrical energy into mechanical energy
uses an electric current to turn an axle

Two magnets are placed on each side of a looped wire
A current is sent through the wire
The wire becomes magnetic
The magnet and magnetic wire repel and the wire makes a half turn
The electric flow of the wire is reversed, switching its magnetism to cause another half turn- finishing the rotation
The process repeats itself
The spinning action powers a machine

What does a generator do and briefly describe how it works?
Wire spinning between magnets makes electricity
a device that transforms mechanical energy into electrical energy (opposite of electric motor)
instead of using an electric current in a magnetic field to produce motion, it uses motion in a magnetic field to produce an electric current

Reverse design of a motor
A force of nature (wind, fire, water falling) spins a looped wire
The magnets force the electrons within the wire to move with each revolution of the wire
The electrons move along the wire in the form of electricity to an appliance

What does it mean to have an alternating current (AC)?
The electric flow goes back and forth
the wire in the magnetic field is moved up and down repeatedly (producing AC)
consists of charges that move back and forth in a circuit
can be easily raised or lowered to a higher or lower voltage
What is the difference between AC and DC?
In AC, the electric flow goes back and forth
better for power plants
the wire in the magnetic field is moved up and down repeatedly
consists of charges that move back and forth in a circuit
can be easily raised or lowered to a higher or lower voltage

In DC, the current moves only in one direction
used in batteries
DC can be induced from a changing magnetic field or produced from an energy source such as a battery.

Why do power plants produce AC power?
This is because AC is used in homes, schools, and other buildings (making it easier to power them)
The power plants can easily raise or lower the voltage, meaning that a high voltage can be sent over great distances and then reduced to a safer level for everyday use. This is the basic job of a power plant, and AC compliments that.
We will write a custom essay sample on
Any topic specifically for you
For only \$13.90/page
What are the different resources used to power generators?
Most power ultimately is produced by a fusion
Energy resources:
Wind
Rivers
Ocean currents
Fossil Fuels
Nuclear plants
Solar Energy
Geothermal Energy
What is a benefit of using renewable energy sources over nonrenewable energy sources?
Renewable energy sources can be naturally and quickly replaced, while nonrenewable energy sources only exist in a limited amount.
What is an electric circuit?
An electrical device that provides a “circular” path for electric current to flow
a complete, unbroken path through which electric charges can flow
Conductors
conduction- when charges move when objects touch
metals such as silver, copper, aluminum are good conductors
a material through which charge can flow easily
atoms contain electrons that are bound loosely and are able to move throughout the conductor and produce an electric current as they flow through a conductor
used to carry electric charge

light flips on so fast because electrons are already present inside of your conductors that make up the circuit
flip the switch: electrons at one end of wire and pulled while those on the other end are pushed, causing a continous flow of electrons through all parts of the circuit as soon as the circuit is complete

Insulators
induction- charge is produced without touch
charges can not flow easily in these materials
electrons in an insulator are bound tightly to their atoms and do not move easily.
rubber, glass, sand, plastic, and wood are good insulators
used to stop the flow of charges
rubber coating of an appliance cord
cord carries charges from an electrical outlet to an appliance
why no shock when touch cord? Ineer wire is a conductor for the current, rubber coating is insulator
cord allows charge to continue to flow, but stops it from flowing into your hands and shocking you.
What is static electricity and how does one get it?
An electrical charge from a buildup of electrons due to friction between two different materials

protons are bound tightly in the center of an atom, but electrons can sometimes leave their atoms.
in materials such as silver, gold, copper, and aluminum some electrons are held loosely by their atoms and can move to other atoms
loose electron- more protons than electrons- positive charge
gain electron- more electrons than protons- negative charge
buildup of charges on an object
charges build up on an object, but they do not flow continuously.

you can get static electricity through:
charge by friction- when two uncharged objects rub together, some electrons from one object can move onto the other object. gain- neg loose- pos
charge by conduction- charged object touches another object, electrons can be transferred between the two. electrons transfer from obj. with more neg charge to the one with more pos charge
charge by induction- objects do not touch when charges transger. the movement of electrons to one part of an object that is caused by the electric field of a second object.
electric field around charged object attracts or repels electrons in the second

How does lightning occur?
Through static discharge
when a negatively charged object and a positively charged object are brought together, electrons transfer until both objects have the same charge.

the loss of static electricity as electric charges transfer from one object to another is called static discharge.
often times producing a spark
as electrons transfer between objects they heat the air around they travel until it glows. glowing air is spark

lightning is a dramatic example of static discharge
during thunderstorms, air swirls violently
water droplets within the clouds become electrically charged causing the bottoms of clouds to become negatively charged, inducing a positive charge on the earth below. Electrons jump between the cloud and Earth’s surface, producing a giant spark as it travels through the air. possible because of the charging by conduction

What is voltage?
the difference in charge between two parts of a circuit (measured in volts)
increasing the difference between the two points, increases the push on electrons
voltage causes a current in an electric circuit
How does one calculate voltage?
voltage= current x resistance
What is an ampere?
Unit for the flow of electric current (named after Andrew-Marie Ampere)
What is resistance and what factors contribute to it?
resistance is things that slow the current
the measure of how difficult it is for charges to flow through a material
greater the resistance, the less current there is for a given voltage
measured in ohms (Ω)

determining factors:
Thickness- thin- more resistance
Length- longer more resistance
Type of material- insulators have high Ω due to fact that difficult for charges to move
resistance= voltage/current

what are the differences between a series circuit and a parallel circuit?
series- only one path for a current to take
If any part of the circuit is broken, the current stops
the current diminishes as resistance adds with each added object
all parts of an electric circuit are connected one after another along one path

parallel circuit- several paths for a current to take
If one part of the circuit is broken, the current can take alternate routes
more paths, more current (amps) across the whole circuit= bright light bulbs

short circuit
the current takes an unintended path
a connection that allows current to take the path of least resistance.
flow through person rather than wire to the power plant (lessΩ)
current can be very high and fatal
what does it mean to have something grounded?
allows current to flow directly to ground if short circuit occurs
provides alternate path for electric current
a wire that connectd all the electric circuits to the ground or Earth
circuit is electrically grounded when charges are able to flow directly from the circuit into the event of a short circuit

can use a third prong or plug: two flat prongs of a plug connect an appliance to the household circuit: third prong, round, connects any metal pieces of the appliance to the ground wire of the building.

Compare and contract a fuse and a circuit breaker
fuse: sections of wire that melts and breaks at a given current
switch that turns off at a given current
contains thin strip of metal that will melt if their is too much current through it.
upon melting, it breaks the circuit which stops current
found in cars and older buildings
must be replaced upon burning out

both prevent circuits from overheating

circuit breaker: doesn’t need to be replaced and used in newer buildings
reusable safety switch that breaks the circuit when the current gets too high.
in some, a small metal band heats up and bends away from wires in the circuit disrupting current
easy to reset, only pull switch back and reconnect metal band to wires

What is a Watt?
unit of power to measure how fast an appliance converts electricity into another form of energy
. power- voltage x current
. watts (p)- Volts (v) x Amps ( I )
Difference between energy and power
The amount of time you use the power from an appliance
what unit is power measured in?
killowatts
what is the formula for Energy?
Energy= Power X Time
Kilowatt-hours=kilowatts x Hours