p7 Flashcards
what is the law of conservation of energy?
energy cannot be created or destroyed. Energy can only be transfered between stores.
what are the different energy stores?
- chemical
- kinetic
- thermal
- gravitational
- elastic
- nuclear
- electrostatic
- magntic
how is energy dissapted so that it is stored in less useful ways?
when energy is transfered to surroundings and so it no longer useful
how do you reduce dissapation (unwanted energy transfer) ?
- friction- lubrication
- heating- insulation
how is energy transferred from batteries/ ac from the main
how do you calculate energy efficency?
energy out/ energy in
*100
what are the ways to increase efficency?
- use insulation to reduce heating of the surroundings
- make devices from materials that reduce unwanted energy transfer
- use technology to produce devices that are better at their jobs
how is the rate of cooling affected by the thickness and thermal conductivity?
- more thickness = longer rate of cooling
- lower thermal conductivity= longer rate of cooling
what is power?
the rate of energy transfer
P= E/T
1 Watt = 1 joule per second
what is the kilowatt hour kWh?
a convince unit used for the measure of energy
1kWatt is used within an hour
define thermal conductivity
- how quickly energy is transferred through a wall of :
- 1m^^2
- a thickness of 1 m
- a temperature difference
- **lower ** thermal conductivity is better becuase less energy will be transferred
use insulation of lower thermal conductivity
how does energy transfered to suurounding less efficent?
canot easily use it becuase energy has become dissapated
how does lubrication reduce energy transfered to the thermal store?
- layer of fluid between two solid surfaces
- the surfaces are no longer in direct contact
- reducing friction
- (friction would dissapate energy )
how does insulation reduce the energy transfered to the thermal store?
- material placed between hot and cold material
- rate of enrgy transfer is reduced
