Y9 Heat and Electricity

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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