Energy Flashcards
use of energy of living things
to stay alive and carry out their daily activities
use of energy of animals and plants
to grow
use of energy of humans
to power our appliances and machines
Forms of energy
- Sound energy
- chemical energy
- light energy
- thermal energy
- kinetic energy
- potential energy
- electrical energy
sound wave
a form of mechanical energy
how does sound travel
it travels through gas, liquids, solids as sound waves
when is sound energy given out
when an object vibrates
chemical energy
energy stored in the bounds of chemical compounds
examples of things that store chemical energy
- food
- fuels (such as wood, charcoal and petrol)
- batteries
use of chemical energy stored in food for humans
to help us stay alive, grow and carry out our activities
when fuels are burned, the chemical energy stored in them is _____
released as other forms of energy
use of chemical energy stored in batteries
provide energy for small electrical appliances and other devices
Light enables us to ____
see things
Use of light for plants
to make food
an object with ______ has more thermal energy
higher temperature
all moving objects have _____
kinetic energy
what is the amount of kinetic energy of an object related to
its speed and mass
the faster an object moves, the more ______ it has
kinetic energy
the greater the _____ of an object, the more kinetic energy it has
mass
when does an object gain potential energy
when it is raised to a higher position
the higher the position of the object, the more _____ it has
potential energy
some objects also store potential energy when they are _____ or _____
stretched or compressed
example of object that gain potential energy when it is stretched
bow
example of object that gain potential energy when it is compressed
pilers
electrical energy is the most widely used ___________
energy form at home
______ need electrical energy to work
all electrical appliances
how is electrical energy supplied
- supplied from power stations, transmitted to our homes through power cables
- obtained from batteries
what are some things in nature that carry electrical energy
lightning, electric eels
units of energy
- joule
- kilojoule
- calorie
- kilocalorie
one cal = ?
4.18 J
where is the unit cal commonly used
for measuring the energy value of food
the process of energy converting into different forms
energy conversion
law of conservation of energy
energy can be converted from one form into another but cannot be created or destroyed
use of sankey diagram
to show an energy conversion process
Energy converters
devices or appliances we use to convert energy from one form into another form of useful energy in daily life
example of an energy converter and how it works
the lamp converts electrical energy into light energy and thermal energy. Light energy is the useful energy which enables us to see things in the dark.
efficiency of an energy converter = ?
Useful energy output / total energy output * 100%
in the sankey diagram, the useful energy output goes ___ and the non-useful energy output goes _____
straight, sideways
heat
energy transeferred from a hotter object to a colder one
processes of heat transfer
- conduction
- convection
- radiation
conduction requires a _______ such as a solid, a liquid or a gas to transfer ____
medium, heat
heat always flows from _____ to ______
hot, cold
conduction can take place in an object, or two objects _______
in contact
good conductors of heat
metals (such as copper and iron)
poor conductors of heat are also called
insulators of heat
poor conductors of heat
non-metal (such as plastic and wood)
water and liquids are ____ conductors of heat
poor
uses of good conductors of heat
- cooking utensils
- heat sink
uses of poor conductors of heat
- handles of cooking utensils
- down clothing
why can down jackets keep us warm
fur and feathers can trap a lot of air inside them. Since air is a poor conductor of heat, we can wear down jackets to keep warm
convection current of air/water
hot air/water rises, cold air/water sinks
process of convection
the convection current carries heat from one place to another
what medium can convection take place in
liquids and gases
definition of convection
the transfer of heat from one place to another by the movement of a liquid/gas
electrical appliances that use convection
- electric kettle
- air conditioner
effects of convection currents in nature
sea breezes and land breezes
the space between the sun and the earth is a ___
vacuum
heat is transferred from the sun to the earth by ______
radiation
hear can be transferred through a vacuum by ______
radiation
________ absorb radiation
all objects
the temperature of an object ____ when it absorbs radiation
increases
dull black surfaces are good ________
while shiny silver surfaces are poor _____________
absorbers and emitters of radiation, absorbers and emitters of radiation
Light-coloured objects absorb ____ radiation than dark-coloured objects
less
____ emit radiation
all objects
applications of radiation in real life
- heat radiator
- cooking utensils
fossil fuels are our main ______
energy sources
examples of fossil fuels
- coal
- crude oil
- natural gas
fossil fuels that are used directly as fuel
coal and natural gas
where is coal mainly used
in power stations to generate electricity
the burning of coal supplies
40% of the world’s electricity
crude oil is ______ to produce several types of fuels
processed
types of fuels produced by crude oil
- pretrol
- LPG
- diesel oil
use of natural gas in some countries and Hong Kong
some countries: for cooking and as fuels in cars
hong kong: for generating electricity and to produce town gas
fossil fuels take a very long time to _______ after they are used. They are called ________ energy sources
replenish, non-renewable
fossil fuels’ reserves are ______
limited
problems of burning fossil fuels
- releases many harmful substances such as lead
- produces a large amount of carbon dioxide
when the harmful substances are released into the air, they cause _______
air pollution
health problems caused by air pollution
- irritate our eyes and throat
- cause dizziness and headaches
breathing in harmful substances for a long time: respiratory diseases such as ashma
______ and _______ can trap heat in the atmosphere
carbon dioxide, nitrogen oxides
trap heat gases increase
–> average temperature _______
–> __________
–> rise in ______
–> low-lying ______ may face a high risk of _______
increases, global warming, sea level, coastal areas, flooding
_______ and _____ can dissolve in rainwater to form ________
sulphur dioxide, nitrogen oxides, acid rain
harms of acid rain
- harm to fish and other aquatic life
- damages trees, plants and buildings made of metals or stone
the burning of fossil fuels cause harm to __________
our health and our environment
nuclear fuel
uranium
is nuclear power a renewable energy source
no
Why is nuclear power a non-renewable energy source
because nuclear fuel (uranium) is non-renewable
about 25% of electricity used in Hong Kong comes from the __________________
Guangdong Daya Bay Nuclear Power Station in Dapeng, Shenzhen
the process in nuclear power station to produce electricity
nuclear fuels undergo reactions which release heat. The heat is used to boil water to steam. The steam drives a turbine, which in turn drives a generator that produces electricity
a small amount of nuclear fuel can generate a ________
large amount of electricity
limitations of nuclear power
- the nuclear fuel supply is limited
- nuclear fuels and the waste produced in nuclear power stations are highly dangerous. They are harmful to our health and cause pollution to the environment. Therefore, they need to be stored and transported properly.
types of renewable energy
- solar energy
- wind power
- hydroelectric power
- biomass energy
solar energy is supplied by ______
the sun
_________ are commonly installed on the roofs of buildings to collect solar energy
solar panels
use of solar energy
to produce hot water or generate electricity
limitations of solar energy
- the energy supply is affected by day length and sunlight intensity
- special equipment is needed to collect sunlight. This equipment is costly to build and install
use of wind power
(then & now)
then: for grinding grains and to move boats and ships
now: converted into electrical energy using wind turbines
wind
the kinetic energy of air
process of generating wind power
when the wind blows, the turbine rotated and drives a generator which produces electricity
limitations of wind power
- the supply of wind power depends on the availability and speed of wind
- wind turbines also cause noise pollution and birds are sometimes killed by the blades of wind turbines
- wind turbines make the landscape look unsightly
process in a hydroelectric power station
the water in the reservoir is at a higher position. when the gates in the dam open, the water in the reservoir will flow down. potential energy of the water is then converted into kinetic energy. the flowing water drives a turbine, which in turn drives a generator to produce electricity
limitations of hydroelectric power
the constuction of large dams destroys local land and water habitats. This causes harm to the animals and plants living there. people living near a dam site may also need to move to other places
when wood, crops and animal waste are burned, the chemical energy stored in them is converted into _____________
heat and light energy
the chemical energy stored in plants or in animal waste
biomass energy
why is biomass energy a renewable energy source
because its supplies can be replenished in a short period of time
use of biomass energy
(then & now)
then: for heating and cooking
now: to extract sugar, starch or oil, produce biofuels with food waste
use of biofuels
to power vehicles, for heating or cooking
limitations of biomass energy
- a large area of land is needed to grow crops used for the production of biofuels. The use of agricultural plants as biofuels may increase the prices of crops
- if unused waste is not treated properly, it may release gases with a foul smell and attract pests such as rats and flies
actions to save energy in daily life
- turn off electrical appliances when they are not in use
- choose electrical appliances with grade 1 energy efficiency labels.
- set the air conditioner to keep a moderate temerpature
- hang clothes to dry instead of using a dryer
- use public transport instead of private vehicles
- use the staircase instead of taking a lift if only a short distance
advantages of grade 1 energy efficiency electrical appliances
they use less energy than the same type of appliance with other ratings
new technologies to save energy
- energy-saving escalator
- double glazing windows
- light tubes
- electric vehicles
energy-saving escalator
it runs at normal speed when people walk near to it, but runs at a slower speed when it is not in use
double glazing windows
it traps a layer of air between two panels of glass. as air is a good insulator of heat, the windows keep the room cool by blocking out the heat from the sun
advantages of double glazing windows
it helps reduce the electricity used by air conditioners
light tubes
they can capture sunlight and reflect it into the building
advantages of light tubes
they cut down the energy needed for lighting
advantages of electric vehicles
they use less energy than petrol cars
we can reduce the use of fossil fuels by saving energy and developing ______________
energy-saving technologies
