3 Thermal Physics Flashcards
Temperature and energy transfer
The relative temperature of two objects determines the direction in which energy passes from one object to the other; energy will tend to pass from the hotter object to the colder object until they are both at the same temperature (or in thermal equilibrium). The energy flowing as a result of conduction, convection, and thermal radiation is what is often called “heat”.
Temperature
is a scalar quantity and is measured in units of degrees Figure 2 Dinner is served! Celsius (°C) or kelvin (K) using a thermometer.
Absolute temperature
Absolute temperature is defined to be zero kelvin at absolute zero (the temperature at which all matter has minimum kinetic energy) and 273.16 K at the triple point of water (the unique temperature and pressure at which water can exist as liquid water, ice, and water vapour).
Internal energy
The internal energy of a substance is the total of the potential energy and the random kinetic energy of all the particles in the substance.
Specific heat capacity
The specific heat capacity (c) of a substance as the energy transferred to 1 kg of the substance causing its temperature to increase c = Q/m△T c = specific heat capacity Q = amount of energy supplied to the object m = mass △T = change in temperature
Specific latent heat
Specific latent heat is the energy required to achieve a change in phase of a material.
Describe Conduction and its formula.
Conduction
Takes place in solids
Movement of heat occurs in two ways
a) use of free electrons
b) vibration of atoms
For a solid of cross sectional area A, length L and temperature diffrence ∆T, between its ends, rate at which energy is transferred is given by:
∆Q/∆t = KA ∆T/L
Were K is conductivity and depends onn nature of the substance.
Describe convection and its formula.
Applys to fluids
Black body radiation
All bodies radiate energy (black body radiation)
Power (P) radiated by a black body is governed by stefan-boltzmann law.
P=e𝜎AT⁴ - Stefan boltzmann law
Name Wien’s displacement law
λmax T = 2.9*10⁻³Km
λmax = Maximum wavelength of the emitted radiation
T = Temperature
Describe the Solar constant
Son emits a total power of about P = 3.9 * 10 ²⁶W
THe average Earth - Sun distance is d = 1.5*10¹¹m
Power per unit area (Intensity) recieved by earth is
INntennsity (I) = P/1πd²
Intennsity is power of radiatoin recieved per unit area
Substituting the values of P and d i nthe above equation we get Solar constant(s)of the earth which is 1400 Wm⁻²
From I = P/4πd² => P = IA
Describe what Albedo is
Albedo is the ratio of power of radiation scattered from the body to the total power inncident on the body
⍺ = total scattered power/total inncident power
It has no units
