P2 Flashcards
What is thermal conductivity?
The energy transfer by conduction through a material depends on thermal conductivity
The greater the thermal conductivity of a material, the more energy per second it transfers by conduction
Are good insulators high or low in thermal conductivity?
Low
Energy transfer through them is as low as possible
What does the energy transfer per second of a insulating material depend on?
- The temperature difference across the material
- The thickness of the material
- The thermal conductivity of the material
How can you reduce energy transfer?
The thermal conductivity should be as low as possible
The thickness of the material should be as thick as practically possible
What are electro magnetic waves?
Electric and magnetic waves that travel through space
Can you see infrared radiation?
No, beyond the red part of the visible spectrum.
Do objects emit infrared radiation?
Yes all objects
What is a perfect black body?
Is an object that absorbs all the radiation that hits it.
It doesn’t reflect radiation
It doesn’t transmit radiation (no radiation passes through it)
A good absorber is also a good…
Emitter
What is the best possible emitter?
What is the radiation that it emits called?
A perfect black body
The radiation emitted by a perfect black body is called black body radiation
No other objects emits or absorbs radiation as effectively as a black body
If an object has a constant temperature, the object emits radiation at the — rate as it absorbs it
Same
When does an object’s temperature increase?
When that object absorbs radiation faster than it emits it
Why do rescue teams use light coloured shiny blankets?
A light shiny outer surface emits a lot less radiation than a dark Matt surface
This keeps the patient warm
What factors affect the temperature of the earth?
The rate of light and infrared radiation from the sun are
- reflected into space or absorbed by earths atmosphere or surface
- emitted from earths surface and atmosphere into space
When an substance is heated, what does its temp rise depend on?
- the amount of energy supplied to it
- mass of substance
- what the substance is
