Thermal physics
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What is gas pressure?
Collisions with gas particles and the walls of there container.
How does gas pressure change? via temperature
At constant volume, increase in temperature causes particles to have more kinetic energy. Increasing frequency and force of collisions.
How does gas pressure change via volume
At constant temperature, Decreasing volume increases pressure as there is less area for the particles to move without colliding with container walls.
Explain solids thermal expansion using kinetic particle model
Increase in temperature causes solids particles to vibrate faster taking more space. Limited by the strong attraction force of solids.
Explain liquids thermal expansion using kinetic particle model
Particles move faster around eachother. Limited by attraction force. (increase is greater than solids)
Explain gases thermal expansion using kinetic particle model
Volume will be size of container. If container is flexible, increasing temperature increases volume. Otherwise, increases pressure.
Uses of thermal expansion?
• 2 metal strips expand at different rates. This can be used to break a circuit with a heating element to control temperature • Expansion of liquids in thermometers
What is evaporation?
When particles break away from liquids surface and form vapour
How does this affect liquids temperature? Relation to sweat?
Only particles high in kinetic energy leave the surface. This reduces the average energy of molecules in the liquid, reducing its temperature Evaporation of sweat keeps body cool as, skin is in contact with an evaporating liquid.
factors affecting evaporation 3 points
• Higher temperature increases particles kinetic energy, allowing more particles to leave surface • Strong air flow across surface carries evaporating molecules away quickly • Increasing surface area increases evaporation
What is thermal conduction? (solids)
Atoms in lattice vibrate more as solid is heated. Attractive forces cause vibrations to be passed on to other atoms.
Why are metals good conductors?
Metals contain sea of delocalised electrons which transfer thermal energy from the hot atoms to cold via colliding.
Describe convection current?
Particles move faster when a fluid is heated, causing the heated particles to be less dense. They rise above the unheated denser particles in circulating motion.
How to stop heat transfer via conduction/convection?
• Place object in a vacuum. • Restrict movement of fluid
How does radiation travel? What is unique about this heat transfer method?
Via infrared rays It can transfer heat through a vacuum
What surfaces/tones are good emitters/absorbers of infrared radiation?
Dull and black surfaces
What surfaces/tones are good reflectors of infrared radiation?
White and shiny surfaces
How does earth gain energy? How to greenhouse gases trap heat?
Earths energy comes from sun’s thermal radiation. The Earth also radiates thermal radiation into space. Determining the Earths temperature. Greenhouse gases absorb radiated heat from the Earth and disperse it in the atmosphere.