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define thermal energy (heat)
the energy contained within a system that’s responsible for its temp
define temperature
a measure of heat/thermal energy, specifically the avg motion/kinetic energy of its particles
law of conservation of energy
energy can neither be created nor destroyed.
define energy
the ability to do work or cause change
(heat) conductor + example
any material which allows thermal energy to easily flow through it
e.g. copper, gold, aluminium, iron
insulator + example
any material which slows down the transfer of energy bc molecules don’t allow transfer of energy easily
e.g. cotton, wool, plastic, rubber
relate conduction to changes in particle energy
conduction occurs when a substance is heated.
particles will gain more energy and vibrate more.
define convection
the transfer of thermal energy through bulk movement of matter. (hot goes up, cold goes down)
define convection currents
created by uneven heating of fluid liquid/gas, which creates the current
relate convection to changes in particle energy.
air is heated = particles gain energy
warm air rises, bc less dense
cool air falls to replace air that has risen.
define radiation
transfer of thermal energy by electromagnetic (EM) waves.
define electromagnetic radiation
the movement of photons
explain how thermal energy is transmitted by radiation
via EM waves
no medium needed for transmission (can travel through vacuums)
describe some effects of heat radiation
warming and cooling objects
sunburn, (heat) stroke
how are conduction and convection different?
conduction: heat transfer occurs btwn objects by direct contact
convection: heat transfer occurs within a fluid
which direction does heat usually flow
hot → cold
summarise conduction
direct contact of particles
occurs in solid, liquid, gas
e.g. handle of utensil
summarise radiation
heat by waves
only radiant energy absorbed
e.g. lightbulb
summarise convection
by bulk movement of matter in a fluid (liquids and gases)
currents.
give 3 uses of heat
cooking
warmth
drying clothes
types of energy
potential, kinetic, thermal, elastic, gravitational, electrical, sound, mechanical, chemical,
scales used to measure temp
celcius, fahrenheit, kelvin
define work
measure of energy transfer that occurs when an object is moved over a distance by an external force
define potential (energy)
stored energy that has the potential to become another form of energy
define kinetic (energy)
the energy an object has bc of its motion
define gravitational
a force that exists among all material objects in the universe
define infrared
type of EM radiation
wavelength longer than visible light but shorter than microwave radiation
define joules
unit for energy (J)
one J = energy exerted by a force of 1 newton over a 1m distance
what is a thermometer
instrument that measures temp
celcius
scale/unit for temp
based on 0 degrees for freezing point of water and 100 deg for boiling point
kelvin
scale/unit for temp
based on absolute zero
no negative temp
absolute zero
coldest possible temp
particles completely still
define absorb
the transfer of energy of a wave to matter as the wave passes through it
define emit
to give off or discharge
what kind of particle has a positive charge and where are they located
proton, nucleus
what kind of particle has a negative charge and where are they located
electrons, outer shells
what does the law of electric charges say abt 2 objects that both have a positive charge?
they repel eachother
what are the two things that make an electric force stronger?
the amt of charge
distance between the two things
what is the name of the region that is around all charged objects?
electric field
3 ways to charge an object
friction
conduction
induction
charging an object - friction
electrons are “wiped” from 1 object to another
charging an object - conduction
electrons move from 1 object to another by direct contact/spark
charging an object - induction
charges in an uncharged metal object change without direct contact w/ a charged object
how do charges move?
must be a difference in potential between 2 positions
electrical conductors
why do we cover electrical cords w/ plastic?
to keep the electricity away from our hands
plastic = insulator ; protects from electric shock
difference btwn insulators and conductors (electricity)
insulators
charges don’t move easily
atoms hold on to their electrons = electrons don’t move freely
conductors
charges can move easily
have electrons that are free to move
what is static electricity?
the electrical charge at rest on an object
what is current and how do you measure it?
the amt of charge that flows past a point in a circuit in 1 second
measured in amperes (A), by an ammeter
what is resistance and how is it measured?
measures how difficult it is for an electric current to flow through wires.
electrons moving around a circuit are slowed down by atoms that make up the wires
measured in ohms (Ω)
what is voltage and how is it measured?
a measure of the difference in potential energy of charged particles.
measured in volts (V) with a voltmeter
equation for voltage
V = I * R
equation for current
I = V / R
equation for resistance
R = V / I
series circuit
only 1 path for electrons to move along
current stops flowing if any lights break/burn out
adding more globes = dimmer lights
globes can’t be individually controlled
parallel circuit
number of branches, each w/ own components
current leaving battery splits, equal amt going down each branch
each globe gets full amt of energy
if one goes down the rest stays up, doesn’t affect brightness
each branch can have its own switch
3 things a circuit must have
an energy source (battery/generator)
energy user (lightbulb, monitor)
wires to connect
problems with series circuits
lights not individually controlled
if one is down the rest will be too
more lights = the less brightness they get
benefits of parallel circuits
1 switch for each branch
1 goes down others stay up
extra globes don’t affect brightness
what happens to the current when more globes are added to a series and parallel circuit?
series: resistance goes up, current goes down
parallel: resistance goes down, current goes up
what happens to voltage across each bulb as more bulbs are added to series circuits?
resistance goes down, current goes up
what is ohm’s law?
amt of current flowing through a circuit depends on the voltage and resistance in a circuit.
current (I) = V/R
Note
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