Energy Transfers Flashcards
(20 cards)
What are the energy stores?
- kinetic - moving has energy in kinetic energy store
- thermal - any object - hotter it is , more energy
- chemical - anything that can release energy by a chemical reaction
- gravitational potential- anything in gravitational field(fall)
- elastic potential - anything stretched
- electrostatic - 2 charges that attract and repel
- magnetic
- nuclear - atomic nuclei release energy from thus store in nuclear reactions
What are the energy transfers?
mechanically - object moving due to force pushing
electrically - charge moving through potential difference
by heating - energy transferred from hot to cold
by radiation
What is the equation linking efficiency, useful energy output and total energy output?
efficiency = useful energy output/total energy output x100
What is the principle of conservation of energy?
energy can be stored, transferred between stores and dissipated - but it can never be created or destroyed. the total energy of a closed system has no net change
Explain the transfer of input energy
energy is only useful when it is transferred from one store to another, which useful devices can do but some input energy will be lost or wasted because of thermal energy store by heating, e.g a motor will transfer its kinetic energy but will also transfer thermal energy stores to the motor and surroundings
the less energy wasted, the more useful
Describe a sankey diagram
thicker arrow, more energy - if arrow goes straight then its used but down when wasted
Describe the energy transfer of a ball rolling up a slope
energy transferred mechanically from kinetic store of ball due to its gravitational potential energy store, some energy transferred mechanically to thermal stores of ball and slope (friction) and then by heating to the thermal energy stores of surroundings (waste)
Describe the energy transfer of a bat hitting a ball
some energy usefully transferred mechanically from kinetic energy store of bat to kinetic energy store of ball, rest is wasted. some energy of bat is transferred mechanically to thermal energy of bat/ball/surroundings, remaining energy is carried away by sound
Describe the energy transfer of an electric kettle boiling water
energy transferred electrically from mans to thermal energy store of kettles heating element, then by heating to the thermal energy store of water, some wasted and transferred by heating from thermal energy of heating element/water to thermal energy stores of surroundings
Describe the energy transfer of a battery powered car
energy transferred electrically from chemical energy of battery to kinetic energy store of car and carried away by lights of headlights, wasteful energy occurs thermal energy stores of car and surroundings and wistfully carried away by sound
Describe the energy transfer of a bunsen burner and beaker
energy transferred by heating from chemical energy store of gas to thermal energy stores of beaker, energy also wastefully transferred by heating to thermal energy stores of stand and surroundings, some energy carried away by light
What is thermal radiation?
transfer of energy by heating by infrared electromagnetic waves and all solids, liquids and gases emit and absorb infrared radiation (bigger the temp difference, the faster energy transferred). an object hotter than its surroundings emits more than absorbs and vice versa.
What is conduction?
process where vibrating particles transfer energy from their kinetic energy store to the kinetic energy stores of neighbouring particles
main form of energy transfer by particles by heating in solids. vibrating particles continue to pass causing a raise in temp
Describe an experiment to demonstrate conduction
clamp w metal bar and beads on one end and heated by bunsen burner on other
- attach beads at regular intervals of metal bar using wax
- hold in clamp and heat other end using bunsen burner
- energy is transferred along bar by conduction and temp increases along rod
- wax holding beads will melt and bead will fall w bead closest first
Describe an experiment to demonstrate thermal radiation
using leslie cube (watertight, hollow cube w 4 different surfaces e.g matt black, shiny black, shiny/matte white)
- place leslie cube on heat proof mat
- boil water and fill cube, hold thermometer by cube and record temp (all sides should be same)
- hold infrared detector a set distance away from 1 face and record amount of IR radiation detected
- repeat for each face, w more being detected from black and matte surfaces than white and shiny and repeat
What is convection? and where can it be seen?
when more energetic particles move from the hotter region to cooler region - and transfer energy as they do
immersion heater:
1. energy transferred from heater coils to thermal energy store of water by conduction
2. particles near coils get more entry and start moving faster (more distance between)
3. reduction in density means hotter water rises above cooler, denser water
4. as hot water rises it displaces the colder water main it sink towards the coils
5. cold water then heated by coils and rises, and so on. this creates convection currents (all about changes in density) going up and around
Describe an experiment to demonstrate convection
- place some purple potassium permanganate crystals in beaker of cold water on one side
- gently heat w bunsen burner
- as temp of water around crystals increase they dissolve, forming a bright purple solution
- carried by convection and so traces out path of convict currents
How can you reduce waste for conduction?
all objects have thermal conductivity (how well objects transfer energy by conduction) - materials w high thermal conductivity transfer energy quickly and so to reduce energy transfers away from a system by conduction use materials w low conductivity.
How can you reduce waste for convection?
to reduce convection you need to stop the fluid moving and prevent convection currents from forming by insulation (clothes, blankets). they trap pockets of air so they air can’t move energy and so has to conduct v slowly thorough the pockets go air and the material in-between which both have low thermal conductivity.
How can you reduce waste for thermal radiation?
some colours and surface will absorb and emit better than others, so to reduce the energy transfers use a surface that is a poor emitter (white shiny)
