19 Thermal Physics Flashcards
Thermal energy
Internal energy of an object due to temperature
Internal energy increase
Energy transfer by heating the object
Work done on the object
Internal energy of an object stays constant
No energy transfer
The energy transfer by heating and work done balance each other out
First law of thermodynamics
The change of internal energy of the object = the total energy transfer due to work dine and heating
Molecules in a solid
Atoms and molecules are held to each other by force due to the electrical charges of the protons and electrons in the atoms. The molecules vibrate randomly about a fixed point. The energy supplied by heating provides enough potential energy of the molecules because they break free from each other
Molecules in liquid
Molecules move around randomly, the forces between molecules are not strong enough to hold the molecules in position
Molecules in a gas
Molecules also move about randomly but much further apart on average than in a liquid. Heating a gas or a vapour makes the molecules speed up and so gain kinetic energy
Internal energy
The internal energy of an object is the sum of the random distribution of the kinetic and potential energies of its molecules
Thermal equilibrium
When no overall heat transfer occurs between two objects at the same temperture
Absolute scale
Temperature scale in kelvins defined in terms of absolute zero
Absolute zero
The lowest possible temperature, the temperature at which an object has minimum internal energy
Temperature rise of an object
Mass of the object
Amount of energy supplied to it
Substance from which the object is made
Specific heat capacity
Substance if energy needed to raise the temperature of unit mass of the substance by 1K without state change
E= mc🔺T
Inversion tube experiment
The gradational potential energy if an object falling in a tube is converted into internal energy when it hits the bottom of the tube.
Tube is inverted each time the spheres hit the bottom of the tube. The temperature of the lead shot is measured initially and after a particular number of inversions
Inversion tube experiment (equations)
Loss of gravitational potential energy for each inversion =mgL
N inversions, loss of gravitational potential energy = mgLN
C = gLn / 🔺T
Electrical energy supplied
Current ✖️ voltage ✖️ heating time
Energy needed to heat the liquid
Mass of liquid ✖️ specific heat capacity ✖️ temperature rise
Melting point
The temperature at which a pure substance melts
Boiling point
The temperature at which a pure liquid at atmospheric pressure
Latent heat of fusion
The energy needed to change the state of a solid to a liquid without change of temperture
Latent heat of vaporisation
The energy needed to change the state of a liquid to vapour without change of temperture
Sublimation
The change of state when a solid changes into a vapour directly
Energy produced changing state
Q = ml
Energy transfer between two objects
- one object exerts a force on the other object and makes it move ( one object does work on the other object)
- energy transfer by heating because of the difference in temperature
specific heat capacity of a metal
electrical energy supplied = heater current x heater pd x heating time
c = IVt / mΔT
specific heat capita of a liquid
electrical energy supplied = current x voltage x heating time
energy needed to heat the liquid- mass of liquid x specific heat capacity of liquid x temperature rise
electric shower
IV = mc ΔT/t
water passes steadily through copper coils heated by an electric heater. the water is hotter at the outlet than the inlet
solar heating panel
energy gained per second by heating the liquid that flows through the panel
mcΔT / t
