P1.1 Transfer of energy Flashcards
The bigger the temperature difference between a body and its surroundings…
, the faster the energy is transferred by heating. QA
5 key points about infrared radiation
- ALL object emit + absorb IR
- hotter the object- more IR it radiates in a given time
- dark, matt surfaces- good absorbers + emitters of IR
- light shiny surfaces- poor absorbers + emitters of IR
- light shiny surfaces- good reflectors of IR
What are the 3 states of matter?
solid, liquid, gas
Describe the arrangement and energy of particles in solids
- Strong forces of attraction hold the particles together in a fixed regular arrangement
- Do not have much energy- vibrate around fixed positions
Describe the arrangement and energy of particles in liquids
- weaker forces of attraction between particles.
- Close together but can move past each other
- irregular arrangement
- more energy than particles in a solid
- move in random directions at low speeds
Describe the arrangement and energy of particles in gasses
- almost no forces of attraction between particles
- have more energy than those in liquids and solids
- free to move
- travel in random directions at high speeds
What happens when you heat a substance?
particles have more kinetic energy .
vibrate or move faster
What is conduction of heat energy?
the process where vibrating particles pass on their extra kinetic energy to neighbouring particles
What is an insulator?
A material that has large spaces between it’s particles so conduct heat energy much slower.
Why are metals good conductors?
There are free electrons, which are free to move around the metal. - more collisions
What is a conductor?
A material that has smaller spaces between its particles (denser) - conduction is faster
Definition of convection
convection occurs when the more energetic particles move from the hotter region to the cooler region and take their heat energy with them.
Why can’t convection happen in solids?
As the particles cant move
Describe convection in a hot water tank
- heat energy transferred fro heat coils to water by conduction
- particles near coils gain more energy- move faster
- particles move apart so water expands + becomes less dense
- hotter water rises above cooler water
- as hot water rises it displaces the colder water, making it sink
- process continues
Describe the process of condensation
- when gas cools, particles slow down- kinetic energy of particles is reduced
- Attractive forces between particles pull them closer together
- if particles get close enough, condensation occurs
Describe the process of evaporation
- liquid temperature increases- particles have more kinetic energy, move faster
- becomes less dense
- weaker attractive forces between particles
- if hot enough, evaporation takes place
When does evaporation occur? (2 factors)
- if particles are travelling in right direction to escape liquid
- if particles are travelling fast enough (enough kinetic energy) to overcome attractive forces of other particles in liquid
Why does the temperature of the liquid in a container decrease as the liquid evaporates?
Particles with the most energy leave the surface of the liquid
So the average energy of the remaining particles goes down
and the lower the average energy of the particles the lower the temperature of the liquid
What increases the rate of evaporation? (4 factors)
- Temperature is higher
- Density is lower- as forces between particles will be weaker
- surface area is larger- more particles will be near the surface to escape
- Airflow over the liquid is greater- so lower concentration of evaporating substance in the air, so air above liquid is replaced more quickly
What increases the rate of condensation?
- Temperature of gas is lower- lower kinetic energy
- Temperature of surfaces gas touches is lower
- Density is higher- forces between particles is stronger
- Airflow is less- concentration of substances in air will be higher
what 4 factors increase the rate at which an object transfers energy by heating (cooling)
- Larger surface area- more infrared waves can be emitted
- Smaller volume- higher proportion of the object will be in contact with the surroundings
- Conductors- metal (Material from which the object is made)
- If object is in contact with a conductor (The nature of the surface with which the object is in contact )
Describe some adaptations humans and animals have to control the rate of heat transfer
- Hairs on skin stand up when cold-traps a thicker layer of insulating air round body
- Body diverts more blood to flow near surface of skin when hot - so more heat can be lost by radiation
- Animals in warm environments have larger ears- large surface area to lose heat by radiation
- Animals in cold environments have smaller ears- small surface area- minimise heat loss by radiation
Describe how a flask is designed to limit heat transfer
- double-walled with a vacuum- stops all conduction and convection
- walls are silvered- reduce heat loss by radiation
- insulating foam- minimises heat conduction
What do U-values measure?
how effective a material is as an insulator
The lower the U-value….
the better the material is as an insulator
How are solar panels used?
contain water that is heated by radiation from the sun
hot water may be used to heat buildings or to provide domestic hot water
What is the specific heat capacity of a substance?
the amount of energy required to change the temperature of 1 kilogram of the substance by 1 degree celsius
The equation for specific heat capacity is E=m x c x q
What do each of the letters stand for and what are they measured in?
E- energy transfer - joules J
m- mass- kilograms kg
q- temperature change- degrees celsius oC
c- specific heat capacity- J/kg oC
What are some types of materials used for insulation?
CAVITY WALL INSULATION- foam squirted into a gap between brick- reduces convection and radiation across the gap.
LOFT INSULATION- thick layer of fibreglass wool laid out across the whole floor reduces conduction and radiation into roof space from ceiling
Name some materials that have a high specific heat capacity
water, concrete, bricks, oil
Why are oil heating systems not as good as water based systems?
as oil has a lower specific heat capacity than water
Describe electric storage heaters
store heat energy at night (when electricity is cheeper) then release it during the day
they store heat using concrete or bricks- high specific heat capacity
Describe why if a window is double glazed rather than single glazed, there is less condensation on the inside of the glass
as double glazing provides better insulation
therefore the inside of the glass is not as cold
Explain the process of conduction through metals
metals have free electrons
the kinetic energy of free electrons increases when the metal is heated
this causes the free electrons to move faster and throughout the metal
free electrons collide with ions in the metal, transferring energy to them
How does plastic foam reduce energy transfer by convection?
Air bubbles are trapped in the foam
and so the air can not circulate and form convection currents
Why is a radiator painted black?
as black is a good emitter of infrared radiation
This gives the maximum rate of energy transferred to the surroundings
Why do radiators have cooling thins?
As the fins increase the surface area, increasing the rate of energy transfer
Why does one kilogram of gas have a much larger volume than one kilogram of solid?
There are strong forces of attraction between the particles in a solid
they hold the particles close together in a fixed position
but in a gas, the forces between the particles is very small
so the particles spread out
Describe why a mirror gets misty when a person uses a shower
water evaporates producing water vapour
the mirror surface is cooler than the air
water molecules hit the mirror and lose energy
This causes the particles to move closer together which causes condensation on the mirror
Why does a heated mirror not become misty if you have a shower?
as the mirror surface is warmer
so the rate of condensation is reduced
Describe how a plastic cap on a flask helps to keep the liquid inside hot
plastic is an insulator
it stops convection currents forming at the top of the flask so stopping energy transfer by convection
also, particles evaporating from the hot liquid cannot move into the surrounding air so the cap stops energy transfer by evaporation
Also it reduces energy transfer by conduction
Describe how the glass container in a flask keeps the liquid inside hot
glass is an insulator so reduces energy transfer by conduction
Describe how the vacuum created in a flask helps to keep the liquid inside it hot
both conduction and convection require particles
so it stops energy transfer between the 2 walls by conduction and convection
Describe how the silvered surface on the inside of the flask helps to keep the liquid inside it hot
silvered surfaces reflect infrared radiation so infrared radiation is partly reflected back towards the hot liquid
silvered surfaces are poor emitters of infrared radiation
they reduce energy transfer by radiation
When there is a bigger temperature difference between water and the surrounding air….
the transfer of energy is faster
Explain why fitting an insulating jacket to a hot water tank saves money
water stays hotter for longer
so heater is on for less time
so the cost of the jacket is soon recovered from the lower energy bills
Explain why copper pipes inside solar panels are painted black?
because black is a good absorber of radiation
therefore there will be a faster transfer of energy
Explain how an alcohol based hand gel makes your hands feel cold
to evaporate, the alcohol requires energy
this energy is taken away from the skin and the skin feels cold
Explain why a liquid cools down when it evaporates
EXAM ANSWER- LEARN
- there are attractive forces between molecules
- only the fastest molecules have enough energy to break away from other molecules
- these molecules escape from the surface of the liquid
- therefore the average speed and energy of the remaining molecules goes down
- the lower the average speed and energy of the molecules, the lower the temperature of the liquid
How is the U-value affected by increasing the amount of insulation?
it decreases
What is meant by the term ‘U-value’?
how EFFECTIVE a material is as an INSULATOR
Why is it important that material X has a high specific heat capacity?
so it can store large amounts of energy
What is specific heat capacity measured in?
J/Kg degrees
Explain how energy is transferred though the metal walls of a can through conduction
- in the metal there are free electrons
- they gain kinetic energy
- free electrons transfer energy to other electrons and ions
- by collision
Give 2 features that would help metal cooling fins to transfer energy quickly to the surroundings
large surface area
black
