The document discusses the kinetic theory of gases and heat radiation. It explains that gases are made up of molecules in random motion, and describes their behavior using concepts like pressure, temperature, mean free path and degrees of freedom. Ideal gases have no intermolecular forces, while real gases do. The document also discusses heat radiation, defining concepts like blackbody radiation, emissivity, and formulating laws like Wien's displacement law and Stefan-Boltzmann law that describe the spectral distribution and emission of blackbody radiation respectively.
Chapter 2 - Mechanical Properties of Fluids.pptxPooja M
MARASHTRA STATE BOARD
CLASS XII
PHYSICS
MECHANICAL PROPERTIES OF FLUIDS
CONTENT
Density and pressure.
Buoyant force and Archimedes' principle.
Fluid dynamics.
Viscosity.
Surface tension.
MAHARASHTRA STATE BOARD
CLASS XI AND XII
CHAPTER 9
CURRENT ELECTRICTY
CONTENT
Electric Cell and its Internal resistance
Potential difference and emf of a cell
Combination of cells in series and in parallel
Kirchhoff's laws and their applications
Wheatstone bridge
Metre bridge
Potentiometer – principle and its applications
Chapter 2 - Mechanical Properties of Fluids.pptxPooja M
MARASHTRA STATE BOARD
CLASS XII
PHYSICS
MECHANICAL PROPERTIES OF FLUIDS
CONTENT
Density and pressure.
Buoyant force and Archimedes' principle.
Fluid dynamics.
Viscosity.
Surface tension.
MAHARASHTRA STATE BOARD
CLASS XI AND XII
CHAPTER 9
CURRENT ELECTRICTY
CONTENT
Electric Cell and its Internal resistance
Potential difference and emf of a cell
Combination of cells in series and in parallel
Kirchhoff's laws and their applications
Wheatstone bridge
Metre bridge
Potentiometer – principle and its applications
This would enable students to explain the emission spectrum of hydrogen using the Bohr model of the hydrogen atom; calculate the energy, wavelength, and frequencies involved in the electron transitions in the hydrogen atom; relate the emission spectra to common occurrences like fireworks and neon lights; and describe the Bohr model of the atom and the inadequacies of the Bohr model.
Rotational dynamics as per class 12 Maharashtra State Board syllabusRutticka Kedare
This ppt is as per class 12 Maharashtra State Board's new syllabus w.e.f. 2020. Images are taken from Google public sources and Maharashtra state board textbook of physics. Gif(videos) from Giphy.com. Only intention behind uploading these ppts is to help state board's class 12 students understand physics concepts.
Introduction to the structure of atoms from the view of a chemist - what are neutrons protons and electrons and how are they organized ? How are electrons organized - in 3 quantum numbers. Experimental evidence from the Bohr model.
This would enable students to explain the emission spectrum of hydrogen using the Bohr model of the hydrogen atom; calculate the energy, wavelength, and frequencies involved in the electron transitions in the hydrogen atom; relate the emission spectra to common occurrences like fireworks and neon lights; and describe the Bohr model of the atom and the inadequacies of the Bohr model.
Rotational dynamics as per class 12 Maharashtra State Board syllabusRutticka Kedare
This ppt is as per class 12 Maharashtra State Board's new syllabus w.e.f. 2020. Images are taken from Google public sources and Maharashtra state board textbook of physics. Gif(videos) from Giphy.com. Only intention behind uploading these ppts is to help state board's class 12 students understand physics concepts.
Introduction to the structure of atoms from the view of a chemist - what are neutrons protons and electrons and how are they organized ? How are electrons organized - in 3 quantum numbers. Experimental evidence from the Bohr model.
Here, Modern Physics is explained very shortly and simply to make people understand that Physics is a very interesting subject to learn and modern physics is more interesting.
kinetic theory of gases ppt by Mr. B.Sesha Sai
If you want this slides you can contact me.
It contains about kinetic theory of gases.
https://s3.amazonaws.com/slideshare-downloads/greencomputing-140321231655-phpapp02.pdf?response-content-disposition=attachment&Signature=4hI1zsgO49PvxxJQxl8fO21u5Mo%3D&Expires=1621927579&AWSAccessKeyId=AKIATZMST4DYZS7SJPXUhttps://s3.amazonaws.com/slideshare-downloads/greencomputing-140321231655-phpapp02.pdf?response-content-disposition=attachment&Signature=4hI1zsgO49PvxxJQxl8fO21u5Mo%3D&Expires=1621927579&AWSAccessKeyId=AKIATZMST4DYZS7SJPXUhttps://s3.amazonaws.com/slideshare-downloads/greencomputing-140321231655-phpapp02.pdf?response-content-disposition=attachment&Signature=4hI1zsgO49PvxxJQxl8fO21u5Mo%3D&Expires=1621927579&AWSAccessKeyId=AKIATZMST4DYZS7SJPXUhttps://s3.amazonaws.com/slideshare-downloads/greencomputing-140321231655-phpapp02.pdf?response-content-disposition=attachment&Signature=4hI1zsgO49PvxxJQxl8fO21u5Mo%3D&Expires=1621927579&AWSAccessKeyId=AKIATZMST4DYZS7SJPXUhttps://s3.amazonaws.com/slideshare-downloads/greencomputing-140321231655-phpapp02.pdf?response-content-disposition=attachment&Signature=4hI1zsgO49PvxxJQxl8fO21u5Mo%3D&Expires=1621927579&AWSAccessKeyId=AKIATZMST4DYZS7SJPXUhttps://s3.amazonaws.com/slideshare-downloads/greencomputing-140321231655-phpapp02.pdf?response-content-disposition=attachment&Signature=4hI1zsgO49PvxxJQxl8fO21u5Mo%3D&Expires=1621927579&AWSAccessKeyId=AKIATZMST4DYZS7SJPXUhttps://s3.amazonaws.com/slideshare-downloads/greencomputing-140321231655-phpapp02.pdf?response-content-disposition=attachment&Signature=4hI1zsgO49PvxxJQxl8fO21u5Mo%3D&Expires=1621927579&AWSAccessKeyId=AKIATZMST4DYZS7SJPXUlhttps://s3.amazonaws.com/slideshare-downloads/greencomputing-140321231655-phpapp02.pdf?response-content-disposition=attachment&Signature=4hI1zsgO49PvxxJQxl8fO21u5Mo%3D&Expires=1621927579&AWSAccessKeyId=AKIATZMST4DYZS7SJPXU
MAHARASHTRA STATE BOARD
CLASS XI
PHYSICS
CHAPTER 1
UNITS AND MEASUREMENT
Introduction
The international system of
units
Measurement of length
Measurement of mass
Measurement of time
Accuracy, precision of
instruments and errors in
measurement
Significant figures
Dimensions of physical
quantities
Dimensional formulae and
dimensional equations
Dimensional analysis and its
applications
MAHARASHTRA STATE BOARD
CLASS XI AND XII
CHAPTER 4
THERMODYNAMICS
CONTENT
Introduction
Thermal equilibrium
Zeroth law of
Thermodynamics
Heat, internal energy and
work
First law of
thermodynamics
Specific heat capacity
Thermodynamic state
variables and equation of
state
Thermodynamic processes
Heat engines
Refrigerators and heat
pumps
Second law of
thermodynamics
Reversible and irreversible
processes
Carnot engine
MAHARASHTRA STATE BOARD
CLASS XI AND XII
CHAPTER 5
OSCILLATIONS
CONTENT
Introduction
Periodic and oscillatory
motions
Simple harmonic motion
Simple harmonic motion
and uniform circular
motion
Velocity and acceleration
in simple harmonic motion
Force law for simple
harmonic motion
Energy in simple harmonic
motion
Some systems executing
simple harmonic motion
Damped simple harmonic
motion
Forced oscillations and
resonance
MAHARASHTRA STATE BOARD
CLASS XI and XII
CHAPTER 6
SUPERPOSITION OF WAVES
CONTENT:
Introduction
Transverse and
longitudinal waves
Displacement relation in a
progressive wave
The speed of a travelling
wave
The principle of
superposition of waves
Reflection of waves
Beats
Doppler effect
MAHARASHTRA STATE BOARD
CLASS XI AND XII
PHYSICS
CHAPTER 7
WAVE OPTICS
CONTENT:
Huygen's principle.
Huygen's principles & proof of laws of reflection/refraction.
Condition for construction & destruction of coherent waves.
Young's double slit experiment.
Modified Young's double slit experiment.
Intensity of light in Y.D.S.E.
Diffraction due to single slit.
Polarisation & doppler effect.
MAHARASHTRA STATE BOARD
CLASS XI AND XII
PHYSICS
CHAPTER 8
ELECTROSTATICS
Introduction.
Coulomb's law
Calculating the value of an electric field
Superposition principle
Electric potential
Deriving electric field from potential
Capacitance
Principle of the capacitor
Dielectrics
Polarization, and electric dipole moment
Applications of capacitors.
Normal Labour/ Stages of Labour/ Mechanism of LabourWasim Ak
Normal labor is also termed spontaneous labor, defined as the natural physiological process through which the fetus, placenta, and membranes are expelled from the uterus through the birth canal at term (37 to 42 weeks
How to Make a Field invisible in Odoo 17Celine George
It is possible to hide or invisible some fields in odoo. Commonly using “invisible” attribute in the field definition to invisible the fields. This slide will show how to make a field invisible in odoo 17.
Unit 8 - Information and Communication Technology (Paper I).pdfThiyagu K
This slides describes the basic concepts of ICT, basics of Email, Emerging Technology and Digital Initiatives in Education. This presentations aligns with the UGC Paper I syllabus.
2024.06.01 Introducing a competency framework for languag learning materials ...Sandy Millin
http://sandymillin.wordpress.com/iateflwebinar2024
Published classroom materials form the basis of syllabuses, drive teacher professional development, and have a potentially huge influence on learners, teachers and education systems. All teachers also create their own materials, whether a few sentences on a blackboard, a highly-structured fully-realised online course, or anything in between. Despite this, the knowledge and skills needed to create effective language learning materials are rarely part of teacher training, and are mostly learnt by trial and error.
Knowledge and skills frameworks, generally called competency frameworks, for ELT teachers, trainers and managers have existed for a few years now. However, until I created one for my MA dissertation, there wasn’t one drawing together what we need to know and do to be able to effectively produce language learning materials.
This webinar will introduce you to my framework, highlighting the key competencies I identified from my research. It will also show how anybody involved in language teaching (any language, not just English!), teacher training, managing schools or developing language learning materials can benefit from using the framework.
Welcome to TechSoup New Member Orientation and Q&A (May 2024).pdfTechSoup
In this webinar you will learn how your organization can access TechSoup's wide variety of product discount and donation programs. From hardware to software, we'll give you a tour of the tools available to help your nonprofit with productivity, collaboration, financial management, donor tracking, security, and more.
The French Revolution, which began in 1789, was a period of radical social and political upheaval in France. It marked the decline of absolute monarchies, the rise of secular and democratic republics, and the eventual rise of Napoleon Bonaparte. This revolutionary period is crucial in understanding the transition from feudalism to modernity in Europe.
For more information, visit-www.vavaclasses.com
Acetabularia Information For Class 9 .docxvaibhavrinwa19
Acetabularia acetabulum is a single-celled green alga that in its vegetative state is morphologically differentiated into a basal rhizoid and an axially elongated stalk, which bears whorls of branching hairs. The single diploid nucleus resides in the rhizoid.
Model Attribute Check Company Auto PropertyCeline George
In Odoo, the multi-company feature allows you to manage multiple companies within a single Odoo database instance. Each company can have its own configurations while still sharing common resources such as products, customers, and suppliers.
Operation “Blue Star” is the only event in the history of Independent India where the state went into war with its own people. Even after about 40 years it is not clear if it was culmination of states anger over people of the region, a political game of power or start of dictatorial chapter in the democratic setup.
The people of Punjab felt alienated from main stream due to denial of their just demands during a long democratic struggle since independence. As it happen all over the word, it led to militant struggle with great loss of lives of military, police and civilian personnel. Killing of Indira Gandhi and massacre of innocent Sikhs in Delhi and other India cities was also associated with this movement.
Honest Reviews of Tim Han LMA Course Program.pptxtimhan337
Personal development courses are widely available today, with each one promising life-changing outcomes. Tim Han’s Life Mastery Achievers (LMA) Course has drawn a lot of interest. In addition to offering my frank assessment of Success Insider’s LMA Course, this piece examines the course’s effects via a variety of Tim Han LMA course reviews and Success Insider comments.
2. 2
Kinetic Theory of Gases and Radiation
3.1 Introduction
The laws of Boyle, Charles, and Gay- Lussac are strictly valid for real gases, only if the
pressure of the gas is not too high and the temperature is not close to the liquefaction
temperature of the gas.
A gas obeying the equation of state PV = nRT at all pressures, and temperatures is an ideal
gas.
3.2 Behaviour of a Gas
A gas enclosed in a container is characterized by its pressure, volume and, temperature.
This is the macroscopic description of the gas. Unlike in the case of motion of the stone, it
is very difficult to understand the behaviour of a gas in terms of motion of a single
particle. The number of particles in the gas is itself so large that any attempt to relate the
macroscopic parameters P, V, T and E with the motion of individual particles would be
futile. This is the approach of kinetic theory of gases.
3.3 Ideal Gas and Real Gas
In an ideal gas intermolecular interaction are absent. Real gases are composed of atoms or
molecules which do interact with each other. If the atoms/ molecules of a real gas are so
far apart that there is practically no interatomic/ intermolecular interaction, the real gas is
said to be in the ideal state. This can happen at sufficiently low density of the real gas. At
low pressures or high temperatures, the molecules are far apart and therefore molecular
interactions are negligible. Ideal gas serves as a model to deduce certain properties of real
gases at least when the real gas is in the ideal state.
3.4 Mean Free Path
Fig.: A gas with molecules dispersed in the
container: A stop action photograph.
Fig.: A typical molecule in a gas executing
random motion.
When a molecule approaches another molecule, there is a repulsive force between them,
due to which the molecules behave as small hard spherical particles. This leads to elastic
collisions between the molecules. The molecules also collide with the walls of the
container. Higher the density, more will be the collisions and smaller will be the mean free
path λ. Smaller the size of the molecule, less is the chance for collision and larger is the
mean free path.
3.5 Pressure of Ideal Gas
The walls of the box are kept at a constant temperature T. The kinetic energy of a
molecule depends on the velocity irrespective of its direction.
3. 3
Fig.: A cubical box of side L. It contains n moles of an ideal gas.
Considering all the molecules, their average y and z components of the velocities are not
changed by collisions with the shaded wall.
After colliding with the shaded wall, the molecule travels to the opposite wall and is
reflected back.
The average of the square of the x component of the velocities is,
3.6 Root Mean Square (rms) Speed
Using ideal gas equation PV = nRT,
where 𝑴𝟎 = 𝑵𝑨m is the molar mass of the gas.
Speed of sound in a gas is 𝑽𝒔 = √
𝜸𝑹𝑻
𝑴𝟎
, where 𝜸 =
𝑪𝑷
𝑪𝑽
is called the adiabatic ratio.
Its maximum value is 5/3, for monatomic gases.
4. 4
3.7 Interpretation of Temperature in Kinetic Theory:
The average total energy E, therefore, is
This equation relates the macroscopic parameter of the gas, T, to the kinetic energy of a
molecule.
3.8 Law of Equipartition of Energy
For a gas at a temperature T, the average kinetic energy per molecule denoted as K E. is
Thus, the mean energy associated with every component of translational kinetic energy
which is quadratic in the velocity components in x, y and z directions is
𝟏
𝟐
𝒌𝑩𝑻 and
therefore the total translational energy contribution of the molecule is
𝟑
𝟐
𝒌𝑩𝑻.
3.8.1 Degrees of Freedom
Degrees of freedom of a system are defined as the total number of coordinates or
independent quantities required to describe the position and configuration of the system
completely.
3.8.2 Diatomic Molecules
Fig.: The two independent axes z and y of rotation of a diatomic molecule.
Monatomic gas like helium contains He atoms. He atom has 3 translational degrees
of freedom. The molecule has 3 translational dof. Thus, for a diatomic molecule,
5. 5
In diatomic molecules like 𝑶𝟐, 𝑵𝟐 and CO, the atoms can oscillate along the internuclear
axis only. This motion adds energy associated with the vibrations to the total energy of
the molecule.
The term E (vibrational) consists of two contributions - one from the kinetic energy term
and the other from the potential energy term.
3.9 Specific Heat Capacity
When the temperature of a gas is increased, even a small rise causes considerable change
in volume and pressure. Mayer’s relation gives an expression that connects the two
specific heats.
3.9.1 Mayer’s Relation
If the gas is heated so that its temperature rises by dT, but the volume remains constant,
then the amount of heat supplied to the gas, d𝑸𝟏, is used to increase the internal energy
of the gas (dE). Since, volume of the gas is constant, no work is done in moving the piston.
The amount of heat supplied to the gas is used to increase the internal energy of the gas
as well as to move the piston backwards to allow expansion of gas
But dE = 𝑪𝑽dT
For one mole of gas,
PV = RT
∴ P dV= R dT, since pressure is constant.
This is known as Mayer’s relation between 𝑪𝑷 and 𝑪𝑽.
The relation then is modified to 𝑪𝑷- 𝑪𝑷= R/J where J is mechanical equivalent of heat.
(a) Monatomic Gases: For a monatomic gas enclosed in a container, held at a constant
temperature T and containing 𝑵𝑨 atoms, each atom has only 3 translational dof.
∴ Molar specific heat at constant volume
(b) Diatomic Gases: According to the law of equipartition of energy, the internal energy of
one mole of gas is
6. 6
The molar specific heat at constant volume will be
For diatomic gas containing non rigid vibrating molecules, internal energy per mole is
The molar specific heat at constant volume will be
(c) Polyatomic Gases: Gases which have molecules containing more than two atoms are
termed as polyatomic gases, e.g., ammonia gas where each molecule has one N atom and
three H atoms.
Polyatomic molecules have more than 1 dof for different modes of vibrational motion.
and the molar specific heats at constant volume and constant pressure are,
∴ 𝜸 =
𝑪𝑷
𝑪𝑽
=
𝟒 + 𝒇
𝟑 + 𝒇
3.10 Absorption, Reflection and Transmission of Heat Radiation
The process of transfer of heat by radiation does not require any material medium since
electromagnetic waves travel through vacuum. Heat transfer by radiation is therefore
possible through vacuum as well as through a material medium transparent to this
radiation. The electromagnetic radiation emitted by the bodies, which are at higher
temperature with respect to the surroundings, is known as thermal radiation.
3.10.1 Interaction of Thermal Radiation and Matter
Whenever thermal radiation falls on the surface of an object, some part of heat energy
is reflected, some part is absorbed and the remaining part is transmitted.
Coefficient of absorption or absorptive power or absorptivity (a): The ratio of amount of
heat absorbed to total quantity of heat incident is called the coefficient of absorption.
Coefficient of reflection or reflectance (r): The ratio of amount of radiant energy reflected
to the total energy incident is called the coefficient of reflection.
7. 7
Coefficient of transmission or transmittance (𝒕𝒓): The ratio of amount of radiant energy
transmitted to total energy incident is called the coefficient of transmission.
3.11 Perfect Blackbody
A body, which absorbs the entire radiant energy incident on it, is called an ideal
or perfect blackbody. Thus, for a perfect blackbody, a = 1. Lamp black or platinum black
that absorb nearly 97% of incident radiant heat, resemble a perfect blackbody.
The surface of one object is well-polished and the surface of the other object is painted
black.
3.11.1 Ferry’s Blackbody
There is a conical projection on the inner surface of sphere opposite the aperture.
Radiation entering through the small hole has negligible chance of escaping back through
the small hole. A heat ray entering the sphere through the aperture suffers multiple
reflections and is almost completely absorbed inside. It gives greater effective area as a
perfect blackbody.
Fig.: Ferry’s blackbody
The inner and outer surfaces are connected by a small hole. The radiation falling on the
block that enters through the hole, cannot escape back from it. When the block is heated
to high temperature, thermal radiation is emitted. This is called cavity radiation and
resembles the radiation emitted by a blackbody.
3.12 Emission of Heat Radiation
For a body, the absorbed radiation increases the kinetic energy of the constituent atoms
oscillating about their mean positions.
When the body is heated, the radiated energy corresponds to shorter wavelengths.
Amount of heat radiated by a body depends on
• The absolute temperature of the body (T)
• The nature of the body – the material, nature of surface – polished or not, etc.
• Surface area of the body (A)
• Time duration of for which body emits radiation (t)
The amount of heat radiated, Q, is directly proportional to the surface area (A) and time
duration (t).
∴ 𝑹 =
𝑸
𝑨𝒕
Dimensions of emissive power are [𝑳𝟎
𝑴𝟏
𝑻−𝟑
] and SI unit is J 𝒎−𝟐
𝒔−𝟏
or W/𝒎𝟐
.
The nature of emitting surface, i.e., its material or polishing is not a physical quantity.
At a given temperature, a perfect blackbody has maximum emissive power.
3.12.1 Coefficient of Emission or Emissivity
The coefficient of emission or emissivity (e) of a given surface is the ratio of the emissive
power R of the surface to the emissive power 𝑹𝑩 of a perfect black surface, at the same
temperature.
8. 8
∴ 𝒆 =
𝑹
𝑹𝑩
For a perfect blackbody e = 1, whereas for a perfect reflector e = 0.
3.13 Kirchhoff’s Law of Heat Radiation and its Theoretical Proof
Consider an ordinary body A and a perfect blackbody B of identical geometric shapes
placed in an enclosure.
If Q is the quantity of radiant heat incident on each body in unit time and 𝑸𝒂 is the
quantity of radiant heat absorbed by the body A, then 𝑸𝒂 = a Q.
Quantity of radiant heat absorbed by body A= Quantity of heat emitted by body A
Or, a Q = R
For the perfect blackbody B,
Q = 𝑹𝑩
a =
𝑹
𝑹𝑩
or,
𝑹
𝒂
= 𝑹𝑩
But,
𝑹
𝑹𝑩
= 𝒆
∴ 𝒂 = 𝒆
3.14 Spectral Distribution of Blackbody Radiation
The radiant energy emitted per unit area per unit time by a blackbody depends
on its temperature. Hot objects radiate electromagnetic radiation in a large range of
frequencies.
As the temperature is increased, rate of emission increases fast. At each temperature, the
radiant energy contains a mixture of different wavelengths. At higher temperatures, the
total energy radiated per unit time increases and the proportion of energy emitted at
higher frequencies or shorter wavelengths also increases.
Lummer and Pringsheim studied the energy distribution of blackbody radiation as a
function of wavelength. They kept the source of radiation at different temperatures and
measured the radiant power corresponding to different wavelengths. The measurements
were represented graphically in the form of curves showing variation of radiant power per
unit area as a function of wavelength λ at different constant temperatures.
Fig. 3.5: Radiant power of a blackbody per unit
range of wavelength as a function of wavelength.
From experimental curves, it is observed that
1. at a given temperature, the energy is not uniformly distributed in the spectrum of
blackbody,
2. at a given temperature, the radiant power emitted initially increases with increase of
wavelength, reaches its maximum and then decreases.
3. area under the curve represents total energy emitted per unit time per unit area by the
blackbody at all wavelengths,
9. 9
4. the peak of the curves shifts towards the left – shorter wavelengths, i.e., the value of
𝝀𝒎𝒂𝒙 decreases with increase in temperature,
5. at higher temperatures, the radiant power or total energy emitted per unit time per
unit area corresponding to all the wavelengths increases,
6. at a temperature of 300 K, the most intense of these waves has a wavelength of about 5
× 𝟏𝟎−𝟔
m; the radiant power is smaller for wavelengths different from this value. These
are infrared radiations.
3.14.1 Wien’s Displacement Law
The wavelength, for which emissive power of a blackbody is maximum, is inversely
proportional to the absolute temperature of the blackbody. This is Wien’s displacement
law.
where b is called the Wien’s constant and its value is 2.897 × 𝟏𝟎−𝟑
m K. 𝝀𝒎𝒂𝒙 indicates the
wavelength at which the blackbody dominantly radiates.
This law is useful to determine temperatures of distant stars, Sun, moon etc.
3.15 Stefan-Boltzmann Law of Radiation
According to this law, “The rate of emission of radiant energy per unit area or the power
radiated per unit area of a perfect blackbody is directly proportional to the fourth power
of its absolute temperature”.
where σ is Stefan’s constant and is equal to 5.67 × 𝟏𝟎−𝟖
J 𝒎−𝟐
𝒔−𝟏
𝑲−𝟒
or W 𝒎−𝟐
𝑲−𝟒
and dimensions of σ are [𝑳𝟎
𝑴𝟏
𝑻−𝟑
𝑲−𝟒
].
If Q is the amount of radiant energy emitted in time t by a perfect blackbody of surface
area A at temperature T, then
𝑸
𝑨𝒕
= 𝝈𝑻𝟒
.
For an ordinary body,
where e is emissivity of the surface.
The energy radiated per unit area per unit time = σ𝑻𝟒
Energy absorbed from surroundings per unit area per unit time = σ𝑻𝑶
𝟒
Therefore, net loss of energy by perfect blackbody per unit area per unit time
For an ordinary body, net loss of energy per unit area per unit time = e𝝈(𝑻𝟒
− 𝑻𝑶
𝟒
)
If the body is at a temperature lower than the surrounding i.e., T < 𝑻𝟎, then e𝝈(𝑻𝑶
𝟒
− 𝑻𝟒
)
will be the net gain in thermal energy of the body per unit area per unit time.