Flashcards in Physics Deck (87)
The hotter an object is the more infrared radiation ...
... It radiates in a given time
Black, matte surfaces are ...
... Good absorbers and emitters of infrared radiation (heat)
Light, shiny surfaces are ...
... Poor absorbers and emitters of infrared radiation but good reflectors
Kinetic theory is used to ...
... Explain the different states of matter
Particles of solids, liquids and gases have ...
... Different amounts of energy
What are particles involved in
The transfer of energy by conduction, convection, evaporation and condensation
What do all objects emit and absorb
What is conduction
When the particles/free electrons/ atoms at the hot and gain energy and vibrate faster. They then pass on their extra kinetic energy and heat to neighbouring particles/atoms/free electrons through diffusion and collision.
What is convection currents
The heated particles becomes less dense therefore rising. The warm air displaces the cooler air and the cool denser air falls.The cool, denser air flows to fill the gap left by the rising, heated air
What is evaporation
Evaporation is when particles escape from the liquid.
What is condensation
When gas cools, the particles in a gas slow down and lose kinetic energy. The attractive forces between the particles pull them closer together. If the temperature gets cold enough and the gas particles get close enough together that condensation can take place, the gas becomes a liquid.
Factors affecting the rate of evaporation
Temperature (higher temperature = faster rate)
Density (lower density = faster rate)
Surface area (larger surface area = faster rate)
Airflow over the liquid (greater airflow = (faster rate)
Factors affecting the rate of condensation
Temperature of the gas (lower temperature = faster rate)
Temperature of the surface the gas touches (lower temperature = faster rate)
Density (higher density = faster rate)
Airflow (less airflow = faster rate)
The rate at which an object transfers energy by heating depends on
Surfaces area and volume
The material from which the object is made
The nature of the surface with which the object is in contact
The bigger the temperature difference between an object and its surrounding…
… the faster the rate at which energy is transferred by heating
What does U-value measure
What does U-value measure
The lower the U-value …
… The better the material is as an insulator
What do certain solar panels contain
Water that is heated by radiation from the sun. This water may then be used to heat buildings or provide domestic hot water
What is the specific heat capacity of a substance
The amount of energy required to change the temperature of 1 kg of the substance by 1°C
Energy transferred = mass x specific heat capacity x temperature change
What is the conservation of energy principle
Energy can be transferred usefully, stored, or dissipated, but cannot be created or destroyed
When energy is transferred …
... Only part of it may be usefully transferred, the rest is 'wasted'
Wasted energy is eventually…
... transferred to the surroundings, which become warmer. The wasted energy becomes increasingly spread out and so becomes less useful
How do you calculate the efficiency of the device
Efficiency = useful energy out /total energy in * 100
What are the differences between the three states of matter
The arrangement and energy of the particles
What happens when you heat a substance
You give its particles more kinetic energy so they vibrate or move faster
How do you know whether a material is a conductor
Conductors are usually dense solids. Their particles are closer together and so collide more often and pass energy between them. This allows conduction to happen faster therefore they are conductors
How do you know whether a material is an insulator
Insulators are materials that have larger spaces between their particles so they conduct heat much more slowly.
How do you calculate payback time
Payback time = initial cost / annual saving
How does cavity wall insulation reduce heat loss
The foam squirted into the gaps between the bricks reduces convection and radiation across the gap. Pockets of air in the foam reduce heat transfer by conduction