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Hawking Radiation: A Comprehensive Guide for Science Students

June 18, 2024February 5, 2023 by Core SME lambdageeks.com

Hawking radiation is a remarkable theoretical concept proposed by the renowned physicist Stephen Hawking, which suggests that black holes can emit thermal radiation due to quantum effects. While directly observing Hawking radiation from astrophysical black holes remains a significant challenge, there have been remarkable advancements in understanding and measuring this phenomenon through analog systems and … Read more

Intensity Of Radiation Equation: Exhaustive Insights

January 21, 2024February 16, 2022 by AKSHITA MAPARI

In this article, we will see different factors on which the intensity of the radiation depends and what is the intensity of the radiation equation.

The intensity of radiation is the power radiated from the object on which the light waves are incident at a certain angle. The energy radiated from the unit area of the object depends upon its rate of emissivity, the temperature of the object, and its dimensions.

Intensity of Radiation Equation and the Solid Angle

The intensity of the radiation is the energy radiated from the system per unit area making a solid angle of radiations. Thus given by the equation,

I=E/Aθ

Where I is the intensity,

A is an area,

E is the energy radiated,

θ is a solid angle

When we measure an angle in three dimensional, we call it a solid angle and is measured in terms of steradians.

The area covered by the cone making an angle ‘θ’ is A=θ r². The radiated waves at an angle ‘θ’ are emitted in this area ‘A’.

Does the intensity of Radiation depend upon Emissivity?

The emissivity of the object depends upon the intensity of the incident waves on the object, dimensions, composition, and colour.

The intensity of the radiation depends upon the emissivity of the object. The dark coloured objects emit very few radiations as compared to bright coloured objects. Hence, the intensity of the radiation will be more in the case of bright coloured objects.

Does the intensity of Radiation depend upon the Temperature?

The intensity of radiation depends upon the intensity of incident waves and the angle at which these waves are incident.

If the temperature of the system is high then the emission of radiation is more from the system. The intensity of light will be responsible for the rise in temperature of the system as the agility of the molecules will increase and thus escalating the radiation intensity.

The power of radiation is directly proportional to the fourth power of the temperature by the formula,

P=ɛ Σ AT⁴

Where P is a radiation power

ɛ is the emissivity of the object

Σ=5.67* 10^-8 W/m²K⁴ is a Stefan’s Constant

A is the area

T is a temperature

As the temperature of the system increases, the intensity of radiation of the system also increases.

Does the Intensity of Radiation depend upon the Wavelength?

The radiation with high intensity basically comprises of waves having high frequency and energy.

As the frequency of the refracted waves decreases on giving off the energy to the system, the emitted waves are of long wavelength and thus less intensity.

If we consider the wavelength of the radiated waves, then now we can write the relation between the intensity and the wavelength by the equation,

I=E/A λθ

Where λ is a wavelength

The wavelength of the waves emitted by the system is always less than the wavelength of the incident waves absorbs by the system. This is because the energy of the incident light is reduced by entering into the denser medium and the energy is absorbed by the system converting it into thermal energy thus raising the temperature of the system.

Graph of Intensity of Radiation v/s Wavelength

The intensity of the wave will be more if the wavelength is small, and as the wavelength increases, the intensity will get reduced. If the wavelength is more, the frequency of the radiation is very less.

Here is a graph of intensity v/s the wavelength of the radiation plotted at different temperatures.

intensity of radiation equation — **Graph of Intensity v/s Wavelength**

The above graph clearly indicates that as the temperature of the system increases, the intensity of the emitted radiations also increases.

The intensity of the radiation is more in the visible spectra this is because the sunlight entering the Earth’s atmosphere has a greater intensity which gets absorbed in the object. Upon emitting, the intensity of the radiated waves is very less as the emitted waves possess a higher wavelength.

Read more on Radiant Intensity.

Does the Intensity of the Radiation depend upon the Distance?

If the object is closer to the source, the radiation incident on the object will be more.

The rays of light received by the object when placed near the source are more, but as the object is moved away from the source, the intensity of the light receiving by the object decreases.

When the object is closer to the source from where the light is incident on the object, then the radiations received per unit area of the object are more. As we increase the distance from the source and the object, the area covered by the rays emitted from the source increases but the radiations received by per unit area is less, thus reducing the intensity of the light.

Graph of Intensity of Radiation v/s Distance

Here is a graph plotted for the variation in the intensity of the radiations seen by increasing the gap between the light source and the luminous object.

As the intensity of the light decreases on expanding the distance from the source, the graph of intensity v/s distance shows a slightly exponential curve.

The intensity of the light depends upon how much light is incident on the object. It is equivalent to brightness. If the intensity of the light is more, then the brightness will be more, and if it is less, then we will have a deem source of light.

Frequency Asked Questions

Does the light reflected from the water have the same intensity as the incident light?

The wavelength of the emitted radiation is more compared to the incident waves.

As the photon of light is incident on the object, the energy of the photon is absorbed by the system due to which the intensity of the radiation is reduced.

Why the intensity of the infrared radiation is less than the visible light?

The intensity of the radiation depends upon the energy of the photon carried by the wave and its frequency.

When the visible ray is absorbed by any object, the radiated waves from the object are of bigger wavelength as compared to visible light, thus the intensity of IR is less than the visible light.

How does the intensity depend upon the area of the object?

The intensity is inversely related to the area of the object.

The smaller the area of the object, the less will be its capacity to absorb the radiation, due to which it will emit the radiation faster than the object will bigger size, on contrary, the intensity of the emitted radiation will be more.

How does the intensity depend upon the energy of the radiation?

If the intensity of the incident light is more, then it is evident that the energy associated with the photon is high.

Intensity is directly proportional to the energy of the radiation. Upon incident, this energy is transmitted to the object on which it is incident, hence the emitted radiations have less energy and are emitted at smaller frequencies.

Also Read:

What is diffuse reflection of radiation

What Is Diffuse Reflection Of Radiation: Detailed Insight And Facts

January 20, 2024January 19, 2022 by Raghavi Acharya

In this post on physics, we will study the detailed insights and facts of what is diffuse reflection of radiation and other features.

The term reflection refers to the incident angle getting reflected at any point. Still, in the case of diffuse reflection, the incident ray of light gets reflected at many points with different angle measurements. It consists of a mixture of reflected rays produced from a single incident ray.

Before knowing the detailed facts of what is diffuse reflection of light let us first concentrate on the meaning of diffuse reflection.

Diffuse reflection of radiation: Concept and insights

The term diffuse refers to the fusion and reflection of radiation, indicating that the electromagnetic wavefronts are reflected from the point of the incident ray.

The diffuse reflection of radiation in total signifies that the ray of light is reflected into several other angles in the same medium when a source of incident ray strikes the rough surface.
The surface on which the radiation waves get reflected will not depend on the angle of the incident ray, and it is known as diffuse surface, and the reason for diverging rays is non-parallel rays and the rough surface.

Examples of diffuse reflection of radiation are a reflection from rough streets, textbook reading, bicycle reflectors.

what is diffuse reflection of radiation — Image: Diffuse reflection of radiation

What is a diffuse reflection of radiation?

Diffuse reflection of radiation is an important physical phenomenon.

It is an essential reflection of light rays produced from the rough surface. The incident ray strikes the uneven dots and scatters into many reflected rays that can observe at different angles in the same medium.

Now let’s focus on the difference between the regular and diffused radiation reflection.

Mention the primary differences between regular reflection and diffuse reflection

The essential fundamental differences between the regular and diffuse reflection of radiation are as follows,

Parameters to define	Regular/ Specular Reflection	Irregular/Diffused reflection
Nature of Surface	Soft or smooth surface	A hard or rough surface
Angle of reflection	Parallel single reflection light	Reflection at different angles
Nature of reflection	Clear images	Blur reflective images
Examples	Sun, microscopes, telescopes, and bulb	Camera

It’s time to know the cause for what is diffuse reflection of radiation.

What is the leading cause for diffuse reflection to occur?

The primary and vital cause for any diffused radiation reflection is the presence of uneven surfaces.

Almost all the material we use in daily life contains some minor irregular imperfections on the surfaces; when a beam of parallel rays focuses on these uneven surfaces, the light travels back in many other directions, which helps produce reflective images.

Therefore, these reflected rays at different angles combine to produce the required reflective image.

Examples of diffuse reflection of radiation

The crucial examples of what is a diffuse reflection of radiation in our daily life are mentioned below,

Reading a newspaper or book
Driving on a wet road
Reflection from clothing
Reflection from paper

Reading a newspaper or book

The primary example of what is a diffuse reflection of radiation is reading a newspaper or any book. As we start to read text, its images are seen on the retina of our eyes, and at the same time, the light gets reflected from us; here, both the rays diffuse and help in reading by not producing our image on the book.

Driving on a wet road

When driving a car at night, and if the road is wet due to heavy rain, it becomes difficult to see the clear road. It happens because the light gets reflected the surface of the road into many different angles forming a blur reflective image that will be not visible to the driver making him drive in difficulty.

Reflection from clothing

When a light ray falls on a cloth, the reflection produced from it will not be clear because the surface of the cloth contains some irregular or uneven surface that makes the light reflect at many angles, making the image diffuse. It is a primary example of what is a diffuse reflection of radiation.

Reflection from paper

The surface of any paper will be somewhat rough and possess a higher degree of diffusion of light. If any ray of light falls on the paper, it will be filtered by some irregularities and diverges from many directions making the image unclear.

So, the above examples of what is diffuse reflection of radiation are essential to be known in real-life.

How can diffused reflection be useful for us in real life?

The diffuse reflection of radiation can be constructive in human life, without which most probably we couldn’t have the ability to see things.

The essential aspects of diffused reflection of radiation are,
Without the help of diffused reflection phenomenon, there would be no use of mirrors and cameras (help us to capture beautiful moments).
It is every creature’s primary and essential ability that helps us see our beautiful surroundings.
Apart from light tubes and the sun, all the things we can see are because of the diffused radiation reflection.

So, these are the paramount importance of what is a diffuse reflection of radiation.

To study about spherical mirror and components, click below

S pherical Mirror

Frequently asked questions on diffused reflection of radiation | FAQs

What do you mean by reflection?

The primary example where we observe reflection is a mirror.

It is an essential physical phenomenon without which we could not see the images of one other. It is a phenomenon in which the incident wavefront of light strikes at a point, changes its direction at a certain angle, and comes back to the same media from which it is made to strike the interface of the medium.

What are the different types of reflection in physics?

There are mainly three essential types of reflection processes we study in physics. They are,

Specular reflection or regular reflection process
Diffused reflection or irregular reflection process
Multiple reflection process

Is irregular and diffused reflection the same?

Irregular diffusion is the other term used to refer to diffused reflection.

In general, diffused reflection occurs on a rough or hard surface. It is a physical phenomenon that occurs when parallel- light rays pass and hit a point and reflect into the same medium in many other directions. It sometimes produces blurry images.

Can we say that diffuse reflection refers to the failure of laws of reflection?

Diffused radiation reflection does not refer to the failure of laws of reflection.

We know that diffused radiation reflection is also referred to as irregular reflection. The main feature of this diffused reflection is that it gets reflected from the rough surface and contains irregularities. However, the incident light gets reflected when it strikes at a particular point. So, it won’t violate the laws of reflection in almost all cases except some.

Why does the diffuse reflection phenomenon fail to produce the reflective images?

The diffuse reflection of the radiation phenomenon produces reflective images of low quality that can signify the failure to produce reflective images.

The uneven surface that makes the parallel beam of light reflected in many other directions reduces the quality of reflective images that makes it appear to blur. We can indicate that diffuse reflection fails to produce proper reflective images from this fact.

How can you differ from diffuse reflection from specular reflection?

The main difference between the two essential types of reflection lies in the surface from which it is produced.

Both regular (Specular) and irregular(diffused) radiation reflections reflect two different surfaces. First, the surface must be soft with no uneven dots for a specular reflection to occur. For a diffuse reflection to occur, the surface must contain uneven dots that make the incident light travel into other directions.

Also Read:

Comprehensive Guide on How Heat is Transferred by Radiation

June 18, 2024October 10, 2021 by Prajakta Gharat

Heat transfer by radiation is a fundamental process in which energy is exchanged through the emission and absorption of electromagnetic waves. This mode of heat transfer is distinct from conduction and convection, as it does not require the presence of a physical medium for the energy to be transmitted. Understanding the principles and mechanisms of radiative heat transfer is crucial in various fields, from astrophysics and climate science to engineering and everyday life.

The Stefan-Boltzmann Law: Quantifying Radiative Heat Transfer

The rate at which an object radiates energy is governed by the Stefan-Boltzmann law, which states that the total energy radiated per unit surface area of a body is proportional to the fourth power of its absolute temperature. Mathematically, this relationship is expressed as:

Radiation rate = k × T^4

Where:
– Radiation rate is the total energy radiated per unit surface area (W/m^2)
– k is the Stefan-Boltzmann constant, with a value of 5.67 × 10^-8 W/m^2·K^4
– T is the absolute temperature of the object (in Kelvin)

This law provides a quantitative framework for understanding the relationship between an object’s temperature and its radiative heat transfer. For example, a body at 300 K (27°C) will radiate approximately 450 W/m^2, while a body at 600 K (327°C) will radiate around 3,600 W/m^2, a nearly eightfold increase.

Wavelength and Frequency Dependence of Thermal Radiation

The wavelength and frequency of the radiated electromagnetic waves are also closely linked to the temperature of the emitting object. This relationship is described by Wien’s displacement law, which states that the wavelength at which the maximum intensity of radiation occurs is inversely proportional to the absolute temperature of the object:

λ_max = b / T

Where:
– λ_max is the wavelength at which the maximum intensity of radiation occurs (in meters)
– b is Wien’s displacement constant, with a value of 2.898 × 10^-3 m·K
– T is the absolute temperature of the object (in Kelvin)

As the temperature of an object increases, the wavelength of the peak intensity of the emitted radiation decreases, and the frequency increases. This phenomenon is responsible for the visible glow of hot objects, such as the coils of an electric toaster or the filament of an incandescent light bulb.

At typical room temperatures, most objects radiate energy in the infrared region of the electromagnetic spectrum, which is invisible to the human eye. However, as the temperature rises, the emitted radiation shifts towards shorter wavelengths, eventually reaching the visible spectrum and appearing as a characteristic color.

Blackbody Radiation and Emissivity

The concept of a “blackbody” is central to understanding the principles of radiative heat transfer. A blackbody is an idealized object that absorbs all incident radiation, regardless of the wavelength or angle of incidence, and emits radiation in a characteristic way determined solely by its temperature.

The radiation emitted by a blackbody is known as blackbody radiation, and it is described by Planck’s law, which relates the spectral radiance (power per unit area per unit solid angle per unit wavelength) of a blackbody to its temperature and the wavelength of the radiation:

B_λ(λ, T) = (2hc^2 / λ^5) / (e^(hc / λkT) – 1)

Where:
– B_λ(λ, T) is the spectral radiance of the blackbody (W/m^2·sr·μm)
– h is Planck’s constant (6.626 × 10^-34 J·s)
– c is the speed of light (3.00 × 10^8 m/s)
– λ is the wavelength of the radiation (in meters)
– k is the Boltzmann constant (1.38 × 10^-23 J/K)
– T is the absolute temperature of the blackbody (in Kelvin)

Real-world objects, however, are not perfect blackbodies, and their ability to emit and absorb radiation is characterized by their emissivity, a dimensionless quantity between 0 and 1 that represents the efficiency of the object’s radiation compared to a blackbody at the same temperature.

The emissivity of an object depends on various factors, such as its material, surface roughness, and temperature. For example, a polished metal surface typically has a low emissivity, while a matte black surface has a high emissivity. Understanding and accounting for the emissivity of materials is crucial in many engineering applications, such as the design of thermal insulation systems and the analysis of radiative heat transfer in industrial processes.

Radiative Heat Transfer in Vacuum and Participating Media

One of the unique features of radiative heat transfer is its ability to occur in the absence of a physical medium, such as in the vacuum of space. This is in contrast to conduction and convection, which require the presence of a material medium for the transfer of energy.

The heat received on Earth from the Sun is a prime example of radiative heat transfer in a vacuum. The electromagnetic waves emitted by the Sun’s surface travel through the void of space and are absorbed by the Earth’s atmosphere and surface, providing the energy that sustains life on our planet.

In situations where the medium between the heat source and the receiver is not a vacuum, the presence of participating media, such as gases, liquids, or solids, can significantly affect the radiative heat transfer process. Participating media can absorb, emit, and scatter the radiant energy, leading to complex interactions and the need for more sophisticated models to describe the heat transfer.

For instance, the Earth’s atmosphere, with its various gases and suspended particles, plays a crucial role in the greenhouse effect, where certain atmospheric components absorb and re-emit infrared radiation, trapping heat and influencing the planet’s climate. Similarly, the design of insulation materials for buildings or spacecraft must consider the radiative properties of the participating media to optimize thermal management.

Applications and Importance of Radiative Heat Transfer

Radiative heat transfer is a fundamental process that underpins numerous applications and phenomena in science and engineering. Some key examples include:

Solar Energy Conversion: The absorption and conversion of solar radiation into useful energy, such as in photovoltaic cells and solar thermal collectors, rely on the principles of radiative heat transfer.
Astrophysics and Cosmology: The study of the universe, from the formation of stars and galaxies to the evolution of the cosmos, heavily depends on the understanding of radiative heat transfer in the vacuum of space.
Thermal Imaging and Remote Sensing: Infrared cameras and other remote sensing technologies utilize the principles of radiative heat transfer to detect and measure the temperature of objects from a distance.
Industrial Processes: Radiative heat transfer plays a crucial role in various industrial applications, such as furnace design, glass manufacturing, and the curing of coatings and paints.
Thermal Management in Electronics: The efficient dissipation of heat in electronic devices, such as computers and smartphones, often involves the optimization of radiative heat transfer mechanisms.
Thermal Insulation and Energy Efficiency: The design of effective thermal insulation systems, both for buildings and spacecraft, relies on the understanding of radiative heat transfer and the mitigation of undesirable radiative heat exchange.
Biomedical Applications: Radiative heat transfer principles are applied in medical imaging techniques, such as infrared thermography, and in the design of medical devices that utilize thermal radiation for therapeutic purposes.

Understanding the fundamental principles of radiative heat transfer and its quantifiable aspects, such as the Stefan-Boltzmann law, Wien’s displacement law, and the concept of emissivity, is essential for advancing scientific research, engineering design, and technological innovation across a wide range of disciplines.

Reference:

Thermal Radiation – an overview | ScienceDirect Topics. (n.d.). Retrieved from https://www.sciencedirect.com/topics/engineering/thermal-radiation
THERMAL RADIATION HEAT TRANSFER. (1971). Retrieved from https://ntrs.nasa.gov/api/citations/19710021465/downloads/19710021465.pdf
Methods of Heat Transfer – The Physics Classroom. (n.d.). Retrieved from https://www.physicsclassroom.com/class/thermalP/Lesson-1/Methods-of-Heat-Transfer
What is radiation heat transfer? | Explained by Thermal Engineers. (n.d.). Retrieved from https://conceptgroupllc.com/glossary/what-is-radiation-heat-transfer/
Thermal radiation – Wikipedia. (n.d.). Retrieved from https://en.wikipedia.org/wiki/Thermal_radiation