Thermal physics Flashcards
Pressure
Force(N)/Area(m^2)
Pressure in liquid
Density x gravity x height
Atmospheric pressure
Density x gravity x height
Manometer
Measures pressure exerted by a fluid
Brownian motion
the random motion of microscopic particles when observed through a microscope
What does the movement of smoke particles tells you about air molecules [3]
1) Air molecules exist
2) Air molecules collide with the smoke particles
3) Air molecules are moving randomly
Change of state [2]
1) The only thing that changes is its energy
2) Changes of state are physical changes and so they are reversible
effect on the pressure of the gas as it heated at a constant volume [3]
1) Pressure increases
2) More frequent collision between the gas molecules and walls of container
3) Because gas particles have more kinetic energy from increased temperature
Define Absolute zero
1) The lowest possible temperature / –273 °C / 0 K
2) Particles have the least kinetic energy
Convert from kelvin to celcius
[celcius]+273= Kelvin
Why do small particles move randomly?
1) Air molecules move randomly
2) Air molecules pushes the small particles around
3) These small particles undergo brownian motion
Evaporation explained using kinetic particle model [2]
1) Higher kinetic energy cause faster moving molecules
2) Molecules escape from the water surface
The movement of the gas molecules
1) High speed
2) Randomly in all directions
Kinetic energy equation
Ek = 1/2mv^2
gravitational potential
ΔEP = mgΔh
Energy conservation [2]
1) Energy cannot be created or destroyed, only transferred from store to store
2) There is a finite amoutn of energy in a closed system that can be transferred from one store to another
Why is energy transfer not 100% efficent
Energy can be dissipated (spread out) to the surroundings by heating and radiation
Why is work done = to energy transfer?
1 joule = 1 Nm
100Nm convert into Joules
100Joules
What are the 2 types of work?
1) A force acting over a distance (Mechanical transfer pathway)
2) A flow of charged particles (electricaly transfer pathway)
Work done on objects in equilibrium
1) When object is in equilibrium all forces acting on the object is balanced
2) Work is done on the object to change its motion
Work done
Force x Distance (moved in the direction force applied)
Unit of work
Joules or Nm
Define Power
1) Amount of energy transferred per unit time (energy per second)
2) Amount of work done per unit time
Useful energy vs Wasted energy
1) Useful energy is energy transferred for its intended purpose
2) Wasteful energy is energy transferred not useful for this purpose
Define efficency
The ratio of useful energy output to total energy input
4 types of energy transfer pathways
1) Mechanical: When a force acts on a body eg. collision
2) Electrical: Electricity transfer energy from a power source, such as a cell delievering it to components in a circuit
3) Heating: Energy can be transferred from radiation conduction, convection
4) Radiation: Light and sound carry energy and can transfer this from 2 points
Efficency %
(Useful energy output/Total energy input) x100
F formula for energy or work
Change in energy(J) / time (s)
Work (Nm) / t (s)
Power formula in a circuit
Voltage x current
Ways energy is stored
1) kinetic,
2) gravitational potential,
3) chemical,
4) elastic (strain),
5) nuclear,
6) electrostatic
7) internal (thermal)
Where do most energy sources on earth come from
The sun
What 3 energy do not come from the sun
1) Geothermal- heat from earth’s core
2) Nuclear- elements that make up a small portion of earth’s crust
3) Tidal- gravitational attraction of the moon
3 fossil fuel
Coal
Natural gas (mostly methane) which is used in domestic boilers and cookers
Crude oil which is refined into petrol, diesel, and other fuels
Define renewable source
A resource that can be replenished as it is used / is replaced (by nature) in less than a (human) lifetime
Hydroelectrical dam
A hydroelectric dam transfers energy from the gravitational potential energy store of the water to its kinetic energy store mechanically to generate electricity
Describe nuclear fusion
Small nuclei fuse together to form bigger nuclei
Why is nuclear fusion not used as an energy source
Fusion requires very high temperatures
That cannot be produced currently
To describe how the wind turbine produces electricity
1) Moving air spins the blades
2) kinetic energy from that turns on a generator
3) Generator produces electrical energy
Explain how the tidal barrage (dam) produces electricity
1) Water has energy in its kinetic store
2) When the tide comes in and out the water goes through the turbine
3) turbine rotates and generates electricity
To describe how energy released from fission reactions is used to generate electricity
1) Energy released from the nuclei fusion is transfered into the thermal store of water to produce steam
2) Steam turns a turbine
3) Turbin turns a generator which generates electricity
Why Pressure is constant at constant depth
Because given it is the same liquid (same density) and on the same planet, the depth is the only factor affecting the pressure, so at the same depth the pressure remains the same
Why do you need a large amount of force to break a small chunk of rock?
1) The attractive forces between atoms in the rock are strong
2) Work must be done to separate the atoms
Why is that when water reaches its boiling point the temperature stops increasing?
All energy is used up by the particle to overcome intermolecular forces of attraction between water molecules, turning them from liquid to gas.
Describe and explain 2 applications of thermal expansion
1) Expansion gaps in railway tracks, in hot weather the tracks expand and can buckle, the gap allows expansion with no damage to the track
2) Expansion gaps in roads, in hot weather the surface expand and can buckle, the gap allows expansion with no damage to the surface
How volatile liquids cool the skin [4]
1) More energetic molecules escape from the liquid
2) molecules with less kinetic energy are left behind
3) Temperature of liquid decreases
4) Thermal energy is lost by skin
Explain why are Liquids are incompressible
1) The molecules are touching
2) There are large intermolecular forces to stop them from moving closer
Define Specific heat capacity
energy / heat required to raise the temperature by 1°C of 1 kg of a substance
Specific heat capacity formula
Change in energy = mass x specific heat capacity x change in temperature
You can find the amount of thermal energy transferred into x substance
Conduction vs convection
1) Conduction is where heat transfer between objects
2) Convection is heat transfer within the fluid
Describe convection in water
1) As the water is heated, energy is transferred to the kinetic energy store of the water molecules, causing them to move faster
2) This increases the volume of the water, and hence decreases its density 3) The warm water rises.
4) Away from the heat the water cools, decreases in volume and falls, creating a convection current
How does these 2 features keep liquid in a vacuum flask warm:
Shiny silver surface
The vacuum between the silvered surface (No particles)
1) Reflects thermal radiation
2) Heat loss by conduction and convection cannot take place because particles are needed for conduction or convection to take place
To describe thermal conduction in terms of particles through a metal [3]
1) The delocalised electrons gain energy
2)Energy is transferred through the metal as electrons move
3) Energy transfer from high to low temperature regions
Describe in terms of molecules why the temperature of a spoon increase when placed in hot liquid
1) The molecules of the hot liquid collide with the surface of the spoon
2) Energy is transferred from the hot liquid to the spoon
3) The amplitude of the vibration of the spoon’s molecules increase, this increases the spoon’s temperature.
State what happens to the volume of molecules When gas changes to solid
Nothing changes
Explain why balloons shrink in size when its cooler in terms of particle theory
1) particles have lower kinetic
energy
2) on average collide less often
3) Thus less pressure on rubber
4) Which pulls balloon material into smaller size
What are the 3 sources of energy that isnt from the sun
1) Geothermal
2) nuclear
3) Tidal
How is energy released in the sun
Nuclear fusion
The research to investigate how energy released by nuclear fusion can be used to produce electrical energy on a large scale is being carried out
JUST FOR U TO KNOW
pV=constant explained
Pressure Volume = constant
for a fixed mass of gas at constant temperature
What does the rise in the temperature of an object also rises?
Its internal energy
Boiling vs Evporating
1) Evaporation is slower, boiling is faster
2) Evaporation leads to cooling. boiling does not
3) Evaporation happens on the surface, boiling occurs throughout
If the temperature T of an ideal gas is constant, then Boyle’s Law is giv
P is proportional to 1/V
The relationship between the pressure and volume for a fixed mass of gas at constant temperature can also be written as
P1 V1=P2 V2 2
Explain why pans have shiny surfaces [2]
1) poor emitters of radiation
2) Reduces energy loss
Explain in terms of particles, why is it difficult to compress liquid? [2]
1) Liquid particles are touching
2) forces between particles are quite huge
