P1.6 Flashcards
What are the 9 types of energy and where can they be found?
electrical - wherever current flows
light - sun.lightbulbs etc
sound - anything noisy e.g loudspeakers
kinetic - anything moving has it
nuclear - only released from nuclear reactions
thermal - flows from hot to colder objects
gravitational potential - possessed by anything that can fall
elastic potential - stretched springs, elastic, rubber bands etc
chemical - possesed by foods, fuels, batteries etc
What is stored energy?
3 forms - gravitational potential
elastic potential
chemical
energy not doing anything, waiting to happen
i.e waiting to be turned on by other forms of energy
What is the principle of the conservation of energy?
energy can never be created or destroyed, only transferred from one form to another
e.g solar hot water panel: light to heat
falling object: gravitational potential to kinetic
electrical devices convert electrical energy into sound, heat, light etc
e.g microphone: electrical to sound
batteries convert chemical energy into electrical to power/run electric devices
e.g toy car batteries: electrical to kinetic,heat,sound,light
Why is only some output energy useful?
machines convert energy from one form to another
total energy output is always the same as energy input. only some is useful as some input energy always lost/wasted (often as heat)
e.g in a car some chemical energy converted into wasted heat and sound energy
when you charge a phone
charger can only convert a small amount of electrical energy into chemical in device battery. most energy is lost as heat
How do you work out efficiency?
tells you the proportion of energy input transferred into useful energy
efficiency = USEFUL energy output/ TOTAL energy input
How can you work out the efficiency of a machine?
you need to know how much energy is supplied to the device and then find out how much useful energy the machine transferred
e.g electrical kettle supplied with 180,000J of electrical energy and 9000J is lost to heat in the room
EFFICIENCY = 171000/180000 x 100 = 95%
What is heat radiation?
consists purely of electromagnetic waves of a certain range of frequencies - aka infrared radiation
continually emitted and absorbed by all objects
an object hotter than surroundings absorbs more radiation than it emits
object cooler than surroundings emits more than it absorbs
can be felt if stand near something hot e.g fire
How does the temperature of an object remain constant?
power is rate of energy change - e/t
for an object to remain a constant temperature, it has to emit and absorb exactly the same amount of heat
What does radiation depend on?
surface colour and texture
dark matt surfaces absorb heat better than bright glossy ones and emit more of it
silvered surfaces reflect nearly a;; radiation that falls on them
e.g solar hot water panels - contain water pipes under black surface. heat radiation from the sun is absorbed by the black surface so the water in the pipes is heated
silver coloured surfaces are good if you need to stop body heat radiating away
e.g survival blankets
What experiments demonstrate factors of heat radiation?
Leslie’s cube - hot water inside the cube and all surfaces different colours. measure temperatures of the surfaces. matt black surface emits most heat so that thermometer gets hottest
The melting wax trick - two identical metal plates, one a mat black back and the other a silvered back. candle in between the two and a wax and ball bearing on opposite sides of each plate. the matt black surface absorbs more heat so it’s wax melts first and the ball bearing drops
