section 4: Energy resources and energy transfers Flashcards
important units:
-kilogram (kg)
-joule (J)
-metre (m)
-metre/second (m/s)
-metre/second² (m/s²)
-newton (N)
-second (s)
-watt (W)
energy stores and energy transfers:
-energy stores: chemical, kinetic, gravitational, elastic, thermal, magnetic, electrostatic, nuclear
-energy transfers: mechanically, electrically, by heating, by radiation (light and sound)
energy transfers: mechanically, electrically, by heating and by radiation
-mechanically e.g. when gravity accelerates an object and gives it kinetic energy
-electrically e.g. when a current passes through a lamp and it emits light and heat
-by heating e.g. when a fire is used to heat up an object
-by radiation e.g. when vibrations cause waves to travel through the air as sound, or an object emits electromagnetic radiation
formula linking efficiency, useful energy output and total energy output
-energy is always conserved, the total energy before is equal to the total energy after
efficiency = useful energy output/total energy output x 100%
-Sankey diagrams can be used to represent the transfer of input energy into useful energy and wasted energy
conduction:
-main method of thermal energy transfer in solids
-metals are extremely good at conducting heat
-non-metals are poor at conducting heat whilst liquids and gases are extremely poor (insulators)
-substance is heated, then atoms start to vibrate more and bump into each other-transferring energy from atom to atom
-delocalised electrons can collide with atoms helping to transfer vibrations through material and heat better
convection:
-main way that heat travels through liquids and gases (can’t in solids)
-when a fluid (a liquid or a gas) is heated:
-molecules push eachother apart- making fluid expand
-this makes the hot fluid less dense than the surroundings
-hot fluid rises, and the cooler fluid replaces it
-eventually, hot fluid cools, contracts and sinks back down again
-resulting motion = convection current
radiation:
-heat transferred by infrared
-the hotter the object, the more infrared radiation it radiates
-colour of object affects how well it emits and aborbs radiation
-black objects-best at emitting + absorbing radiation
-shiny objects-worst at emtting + absorbing radiation
practical: investigate thermal energy transfer by conduction, convection and radiation
- set up the equipment
- using a small amount of petroleum jelly, attach a drawing pin to the end of each of the rods
-try to make this the same amount of petroleum jelly for each rod - bring together the other ends of the rods (without the pins) so that they can each be heated the same amount
- using a bunsen burner, begin heating the ends of the rods without the pins and start the stopwatch
- record the time taken for the pins to fall off the end of each rod and use this to determine the order of conductivity of the metal
-the first pin to fall will be from the rod that is the best conductor
work done:
-work is done when a force moves something through a distance (whenever energy changes forms), the work done is equal to the energy transferred
work done = force x distance
W = Fd
gravitational potential energy:
-the conservation of energy produces a link between gravitational potential energy, kinetic energy and work. For example, when a ball is dropped, gravity does work on it and its gravitational potential energy becomes kinetic energy as it accelerates downwards:
kinetic energy = 1/2 x mass x speed²
Ek = 1/2mv²
gravitational potential energy = mass x gravitational field strength x height
Ep = mgh
power:
-power is the rate at which energy is transferred or the rate at which work is done. For example, a lamp with a greater power will be brighter because it transfers more energy from electrical energy to light and heat energy in a given time
power = work done/time taken
P = W/t
