P1 Conservation and Dissipation of Energy Flashcards
What are the energy stores?
magnetic
internal (thermal)
chemical
kinetic
electrostatic
elastic potential
gravitational potential
nuclear
What are the energy transfers?
In each of these examples, energy is
transferred
by one of the following four types of energy transfer:
mechanical work - a force moving an object through a distance
electrical work - charges moving due to a
potential difference
heating - due to temperature difference caused electrically or by chemical reaction
radiation - energy transferred as a wave, eg light and infrared - light radiation and infrared radiation are
emitted from the sun
What is dissipation and what are some examples to combat it?
Dissipation is a term that is often used to describe ways in which energy is wasted. Any energy that is not transferred to useful energy stores is said to be wasted because it is lost to the surroundings. Electrical cables warming up are a good example of this. It is not useful to have hot wires behind a television as energy is dissipated to the surrounding air.
In a mechanical system, energy is dissipated when two surfaces rub together. Work is done against
friction which causes heating of the two surfaces - so the internal (thermal) energy of the surfaces increases. Adding
lubricant between the surfaces reduces this friction and so less heat is wasted, like on a conveyor belt for example.
What is the conservation of energy?
Energy can be transferred
usefully, stored or dissipated, but it cannot be created or destroyed.
In all cases, energy comes from one store and is transferred to another store. This means that all the energy in the Universe was present at the
Big Bang
and will still be around at the very end of time.
What is the equation for kinetic energy (Ek)
1/2 x mass x speed^2
What is the unit for energy and work?
Joules(J)
What is the equation for elastic potential energy?
1/2 x spring constant x extension^2
What is the formula for Work Done(W)
W=Force(F)x Distance moved along the line of the action of force(Metres,m)
What is the formula for Gravitational potential energy (Ep)
Gravitational potential energy = mass × gravitational field strength × height
mxgxh
What is work done?
Energy transferred by a force
What is the formula for Power, P (Watts, W)
power=work done/time
P=W/t
1 watt= 1 joule per second
What’s the difference between efficient and inefficient devices?
A very efficient device will waste very little of its input energy.
A very inefficient device will waste most of its input energy.
What is the formula for efficiency?
percentage efficiency=useful energy transferred/total energy supplied x100
you can also replace energy with power
What are the useful and wasted stores of energy for a washing machine?
Useful stores - kinetic energy of the drum, internal (thermal) energy of the water.
Wasted stores - sound radiation and infrared radiation dissipated to the surroundings.
