Energy transfers Flashcards
What is the Principle of Conservation of Energy?
Energy can neither be created not destroyed: it can only be transformed from one state to another
What is conduction?
The process where vibrating particles pass on their extra kinetic energy (or heat) to neighbouring particles
How would you calculate efficiency?
Efficiency = (energy output ÷ total energy output) x 100
Why is conduction most effective in solids?
Because the particles are close together and strongly bound to each other
Why are metals good conductors of heat?
They contain free electrons that assist in transferring kinetic energy
What is convection?
When the more energetic particles move from the hotter region to the cooler region and take their heat energy with them
What is radiation?
The emission of infrared waves (The hotter an object the more radiation)
What are the best/worst emitters/absorbers of radiation?
Best- matt black Worst- shiny silver surfaces
Role of convection in weather? (And use)
Thermals are warm current of air
gilder pilots and birds use them to rise higher
How to reduce conduction in housing?
Cavity wall insulation Double glazing Loft insulation
How to reduce convection in housing?
Loft insulation Draught excluders
How to reduce radiation in housing?
Reflective foil behind radiators
Why does trapped air reduce heat loss?
Because the air cannot circulate and is a very poor conductor
If someone is dangerously cold how would you warm them up?
Wrap them in a highly reflective ‘space’ blanket They reflect thermal radiation and prevent convection
How would you calculate the work done?
Work done (J) = force (N) x distance moved (m) fd
When is work done?
When a force makes something move in the direction of the force
How do you calculate the energy transferred?
It is equal to the work done
How would you calculate the gravitational energy?
GPE (J) = Mass (kg) x g x height (m) (G is gravitational field strength) mgh
How would you calculate the kinetic energy?
Kinetic energy (J) = 1/2 x mass (kg) x speed (m/s) 1/2mv²
What’s the relationship between KE and GPE
They are equal in some situations mgh = 1/2mv²
How would you calculate the power?
Power (W) = work done (J) ÷ time taken (s)
Types of energy we need to know:
Thermal (heat) energy, light, electrical, sound, kinetic (movement) energy, chemical energy, nuclear energy, gravitational potential energy and elastic potential energy.
What does ‘wasted’ or ‘lost’ energy actually mean?
‘Wasted’ energy can mean ‘lost’ from the system or converted into unwanted forms. Like the noise produced by a motor when what we want is kinetic energy.
Describe the energy transfers taking place when you strike a match.
You provide some KE as you drag the match head across the striking paper and this is converted into thermal energy; this heat starts the chemical reaction that concerts the chemical energy into thermal energy and light (and a tiny bit of sound).
What is power?
Power is the rate of transfer of energy or the rate of doing work
