P7 Flashcards
What is a chemical energy store?
Eg: glucose in your muscles with oxygen
Energy between chemical bonds
What is gravitational energy store?
A skier at the top of a hill
E= m✖️g(10N/kg)✖️h
What is a nuclear energy store?
Hydrogen from the sun
E = m ✖️velocity of light squared
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
Is having a device with a high power cheaper to run? (6 points)
. higher power devices transfer elecetrical energy faster to other forms
.in the same time they will use more energy
. so will cost more
.however if it is more efficent
. it won’t need to be on for a long amount of time
. so may use less energy , costing less money
what is the law of conservation of energy?
energy can not be created or destroyed only transferred
what is a thermal energy store?
the vibrations of the particles in the object. In hotter objects, the particles vibrate faster.
E=Mcø
what is a kinetic energy store?
associated with a moving objecting
E = 1/2 m v²
what is a gravitational energy store?
an object at height
E= m g h
(g=10N/kg)
what is a elastic energy store?
when an object is stretched, squashed or twisted
E= 1/2 k e²
what is the efficiency equation?
USEFUL output energy transfer/ input energy transfer
what are wasted energy transfers ?
transfers that you didn’t want to happen , eg:heat being transferred to the surroundings
when will a thermal energy transfer occur?
when there is an energy difference between two points
when is energy transferred to the surroundings as heat ?
when a system is not closed (external forces are acting on it)
why is energy from the surroundings not useful?
it cannot be easily transferred to operate a task
what does the rate of heat energy , between walls depend on?
temperature gradient
area of walls
thickness of walls
material of wall(thermal conductivity)
how does the area of walls affect energy transfer?
the greater the area of the walls, the greater the rate of heat energy transfer
how does the thermal conductivity of walls affect the energy transfer?
the lower the thermal conductivity, the (better)less heat loss
what is thermal conductivity ?
the heat energy transfered per second through a 1m thick wall , of area 1m² whe a temperature difference of 1 degree exist
why would you want to reduce heat loss?
more cost effective (heating)
how do you improve the efficiency of a friction causing heating?
lubricate the part
how do you improve the efficiency of a wire causing heating?
choose a wire with a small resistance
how do you improve the efficiency of air resistance causing heating of vehicles?
make it more steamline
how do you improve the efficiency of a machines causing sound?
tighten loose parts to reduce vibration
