EX unit four: energy resources and energy transfer Flashcards
energy is neither created nor destroyed, it is….
converted from one form to another
energy stores
kinetic, gravitational, elastic potential, magnetic, electrostatic, nuclear, thermal and chemical
how is energy transferred by heating
energy is transferred from the hotter object to the cooler one, and the difference in temperature between them decreases.
how is energy transferred mechanically
energy can be transferred mechanically through the movement of the parts in machines, and when the motion or position of an object changes.
how is energy transferred electrically
when an electrical circuit is complete. internal energy stored in the battery is transferred to moving charged particles in the wire.
how is energy transferred by radiation
visible light, infrared, microwaves and radio waves are all forms of radiation, and are carried by waves (and are able to go through empty space).
what do sankey diagrams show
the energy transfers that take place in a system like a motor car. they should show that energy is conserved, but comes out in different forms.
total energy in =
total energy out
efficiency =
useful energy output / total energy input
what is efficiency usually given as, and how do you calculate it
a percentage by multiplying the equation by 100(%)
conduction
the transfer of thermal energy through a substance without the substance itself moving
how does conduction work
an increase in temperature means an increase in the average amount of kinetic energy of the molecules of the substance. this kinetic energy can be transferred from molecule to molecule in solids, passing the heat along.
why is conduction faster in metals
because electrons are free to move and can carry the energy much more quickly.
convection
thermal convection is the transfer of heat energy through fluids by the upward movement of warmer, less dense regions in the fluid.
how does convection work
when a fluid is heated it expands. this means that the density becomes lower, and the warmer fluid floats upwards as it is pushed out of the way by the colder and therefore denser fluid.
radiation
thermal radiation is the transfer of heat energy in the form of infrared waves. it is the only method of heat transfer through a vacuum.
dark surfaces ______ more radiation, so heat up faster.
absorb
matte surfaces _______ and _______ more radiation than light surfaces so heat up faster.
absorb
emit
dark surfaces _______ more radiation than light surfaces, so cool down faster.
emit
matte surfaces _______ more radiation than shiny surfaces so cool down faster.
emit
what does insulation in a house aim to do
reduce the rate of heat transfer between areas at different temperatures.
how to reduce heat transfer by conduction
use a vacuum, use air, use water.
