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Flashcards in Physics Deck (87)
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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

Infrared radiation


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


How does loft insulation reduce heat loss

The thick layer of fibreglass wool laid out across the loft floor and ceiling reduces heat loss from the house by conduction and convection