Prevost's Theory of Heat Exchange : Prevost's theory of heat exchange is that all bodies emit continuous thermal radiation; it doesn't matter what the temperature is or what their surroundings are. Emission depends on a body's nature and temperature, not whether or not there are other bodies around.Read more
Prevost’s Theory of Heat Exchange :
Prevost’s theory of heat exchange is that all bodies emit continuous thermal radiation; it doesn’t matter what the temperature is or what their surroundings are. Emission depends on a body’s nature and temperature, not whether or not there are other bodies around. In contrast to the emission, bodies absorb radiation from their surroundings.
Heat exchange happens between two bodies because of the difference in temperatures of those bodies. The hotter body radiates more energy than it absorbs, whereas the cooler body absorbs more energy than it radiates. This means that there is a net transfer of heat from the hotter body towards the cooler. When a body is in thermal equilibrium with the surroundings, it radiates as well as absorbs energy at the same rate. In this case, there is no net transfer of heat. This process is dynamic, as radiation as well as absorption is in continuous motion. Good Absorbers are Good Radiators :
By Prevost’s theory, a good absorber is also a good radiator.
This is because the properties that enable a surface to absorb energy efficiently allow it also to emit energy efficiently. For instance, black surfaces, which are excellent absorbers of radiation, are also excellent radiators. The relationship is quantified by Kirchhoff’s Law, which asserts that the emissive power of a body is proportional to its absorptive power at the same temperature and wavelength.
Experimental Observations Relevant to Kirchhoff's Law of Heat Radiation: Kirchhoff's law of heat radiation states that for a body in thermal equilibrium, the ratio of its emissive power to its absorptive power is constant and equal to the emissive power of a perfect blackbody at the same temperatureRead more
Experimental Observations Relevant to Kirchhoff’s Law of Heat Radiation:
Kirchhoff’s law of heat radiation states that for a body in thermal equilibrium, the ratio of its emissive power to its absorptive power is constant and equal to the emissive power of a perfect blackbody at the same temperature. Several experimental observations confirm this law:
1. Emission and absorption by black bodies:
Black bodies are perfect absorbers and thus also the best emitters of radiation. Experiments on cavity radiators, that approximate black bodies, demonstrate that their radiation spectrum does indeed behave according to theory, for example Planck’s law, as demanded by Kirchhoff’s principle.
2. Properties of surfaces and radiation:
Blackened surfaces absorb more radiation and emit more heat, while polished surfaces, which are poor absorbers, are also poor emitters. Comparative experiments confirm the law’s validity.
3. Absorption lines in stellar spectra:
Kirchhoff’s law accounts for the absorption lines that appear in stellar spectra. These lines arise from gases in the atmosphere of the star absorbing certain wavelengths of light emitted by the hotter interior, which proves that a good absorber is also a good emitter.
4. Cooling and heating experiments:
Objects with high absorptivity, such as black surfaces, cool faster because they radiate heat more efficiently than reflective surfaces.
5. Greenhouse effect research:
The gases like carbon dioxide and water vapor are able to absorb infrared radiation strongly as well as radiate heat effectively. These observations have been established experimentally, which are central to the studies on climate.
The above results clearly illustrate that a body which absorbs and emits radiations have reciprocal characteristics.
Latent heat of vaporization is about the change in phase from liquid to gas; it involves breaking almost all the intermolecular bonds. Such a process needs much more energy. - The latent heat of fusion involves the change from the solid state to liquid, where just some intermolecular bonds are releaRead more
Latent heat of vaporization is about the change in phase from liquid to gas; it involves breaking almost all the intermolecular bonds. Such a process needs much more energy.
– The latent heat of fusion involves the change from the solid state to liquid, where just some intermolecular bonds are released; therefore, less energy is required.
– Usually, the latent heat of vaporization is much higher than the latent heat of fusion for the same substance.
Explanation: As the temperature of a substance is increased, it emits thermal radiation, and its color changes because the radiation spectrum shifts towards shorter wavelengths: 1. When the temperature is lower, the substance emits infrared radiation, which is not visible. 2. With increasing temperaRead more
Explanation:
As the temperature of a substance is increased, it emits thermal radiation, and its color changes because the radiation spectrum shifts towards shorter wavelengths:
1. When the temperature is lower, the substance emits infrared radiation, which is not visible.
2. With increasing temperature, it begins to emit red light which is the first coloured light.
3. The glow now becomes yellow with further heating and eventually goes white when the emitted light ranges over a bigger spectrum, covering the whole visible wavelengths.
This happens to be due to blackbody radiation and Planck’s law in which higher temperatures correspond to higher-energy radiation while, at the same time, there is a shift in the emission spectrum.
Wien's Displacement Law states that the wavelength (λ_max) at which the intensity of radiation emitted by a black body is maximum is inversely proportional to its absolute temperature (T). In other words, as the temperature of the black body increases, the wavelength at which it emits the most radiaRead more
Wien’s Displacement Law states that the wavelength (λ_max) at which the intensity of radiation emitted by a black body is maximum is inversely proportional to its absolute temperature (T). In other words, as the temperature of the black body increases, the wavelength at which it emits the most radiation decreases.
Mathematically, Wien’s Displacement Law is given as:
λ_max = b / T
where:
– λ_max is the wavelength at which the emission intensity is maximum,
– T is the absolute temperature of the black body in Kelvin (K),
– b is Wien’s displacement constant, approximately 2.898 × 10⁻³ m·K.
Illustration:
– Object at 300 K: Using Wien’s Displacement Law, we calculate the wavelength where its radiation peaks.
λ_max = (2.898 × 10⁻³) / 300 = 9.66 μm
This is in the infrared region.
– Object at 600 K: The peak wavelength of emission is twice the object at 300 K since the temperature has an inverse proportionality to peak wavelength.
λ_max = (2.898 × 10⁻³) / 600 = 4.83 μm
It is still within the infrared, but shorter now.
Relevance of Wien’s Displacement Law:
1. Temperature Determination from Radiation:
Temperature of any object could be determined by the peak wavelength of emitted radiation under the law. It finds many applications in astrophysics, for example, to estimate the temperature of stars as a function of the color of stars. Therefore, it gives a color equivalent estimation.
2. Color of Stars
According to Wien’s law, hotter stars emit more radiation at shorter wavelengths, causing them to appear bluer, and cooler stars emit at longer wavelengths, making them appear redder.
3. Thermal Radiation Understanding:
Wien’s law helps us understand the nature of thermal radiation and how temperature affects the radiation emitted by objects, which is vital in many fields, including climatology and energy studies.
4. Temperature Measurement Applications: The law is applied in infrared thermometry, which allows objects to be measured for temperature without direct contact. This is found in industrial, medical, and scientific applications.
Write the main features of Prevost’s theory of heat exchange. How does this theory lead to the fact that good absorbers are good radiators?
Prevost's Theory of Heat Exchange : Prevost's theory of heat exchange is that all bodies emit continuous thermal radiation; it doesn't matter what the temperature is or what their surroundings are. Emission depends on a body's nature and temperature, not whether or not there are other bodies around.Read more
Prevost’s Theory of Heat Exchange :
Prevost’s theory of heat exchange is that all bodies emit continuous thermal radiation; it doesn’t matter what the temperature is or what their surroundings are. Emission depends on a body’s nature and temperature, not whether or not there are other bodies around. In contrast to the emission, bodies absorb radiation from their surroundings.
Heat exchange happens between two bodies because of the difference in temperatures of those bodies. The hotter body radiates more energy than it absorbs, whereas the cooler body absorbs more energy than it radiates. This means that there is a net transfer of heat from the hotter body towards the cooler. When a body is in thermal equilibrium with the surroundings, it radiates as well as absorbs energy at the same rate. In this case, there is no net transfer of heat. This process is dynamic, as radiation as well as absorption is in continuous motion. Good Absorbers are Good Radiators :
By Prevost’s theory, a good absorber is also a good radiator.
This is because the properties that enable a surface to absorb energy efficiently allow it also to emit energy efficiently. For instance, black surfaces, which are excellent absorbers of radiation, are also excellent radiators. The relationship is quantified by Kirchhoff’s Law, which asserts that the emissive power of a body is proportional to its absorptive power at the same temperature and wavelength.
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Describe some experimental observations to which Kirchhoff’s law of heat radiation is applicable.
Experimental Observations Relevant to Kirchhoff's Law of Heat Radiation: Kirchhoff's law of heat radiation states that for a body in thermal equilibrium, the ratio of its emissive power to its absorptive power is constant and equal to the emissive power of a perfect blackbody at the same temperatureRead more
Experimental Observations Relevant to Kirchhoff’s Law of Heat Radiation:
Kirchhoff’s law of heat radiation states that for a body in thermal equilibrium, the ratio of its emissive power to its absorptive power is constant and equal to the emissive power of a perfect blackbody at the same temperature. Several experimental observations confirm this law:
1. Emission and absorption by black bodies:
Black bodies are perfect absorbers and thus also the best emitters of radiation. Experiments on cavity radiators, that approximate black bodies, demonstrate that their radiation spectrum does indeed behave according to theory, for example Planck’s law, as demanded by Kirchhoff’s principle.
2. Properties of surfaces and radiation:
Blackened surfaces absorb more radiation and emit more heat, while polished surfaces, which are poor absorbers, are also poor emitters. Comparative experiments confirm the law’s validity.
3. Absorption lines in stellar spectra:
Kirchhoff’s law accounts for the absorption lines that appear in stellar spectra. These lines arise from gases in the atmosphere of the star absorbing certain wavelengths of light emitted by the hotter interior, which proves that a good absorber is also a good emitter.
4. Cooling and heating experiments:
Objects with high absorptivity, such as black surfaces, cool faster because they radiate heat more efficiently than reflective surfaces.
5. Greenhouse effect research:
The gases like carbon dioxide and water vapor are able to absorb infrared radiation strongly as well as radiate heat effectively. These observations have been established experimentally, which are central to the studies on climate.
The above results clearly illustrate that a body which absorbs and emits radiations have reciprocal characteristics.
Click here:
See lesshttps://www.tiwariacademy.com/ncert-solutions/class-11/physics/chapter-10/
The latent heat of vaporisation of a substance is always
Latent heat of vaporization is about the change in phase from liquid to gas; it involves breaking almost all the intermolecular bonds. Such a process needs much more energy. - The latent heat of fusion involves the change from the solid state to liquid, where just some intermolecular bonds are releaRead more
Latent heat of vaporization is about the change in phase from liquid to gas; it involves breaking almost all the intermolecular bonds. Such a process needs much more energy.
– The latent heat of fusion involves the change from the solid state to liquid, where just some intermolecular bonds are released; therefore, less energy is required.
– Usually, the latent heat of vaporization is much higher than the latent heat of fusion for the same substance.
Click for more:
See lesshttps://www.tiwariacademy.com/ncert-solutions/class-11/physics/chapter-10/
On increasing the temperature of a substance gradually, its colour becomes
Explanation: As the temperature of a substance is increased, it emits thermal radiation, and its color changes because the radiation spectrum shifts towards shorter wavelengths: 1. When the temperature is lower, the substance emits infrared radiation, which is not visible. 2. With increasing temperaRead more
Explanation:
As the temperature of a substance is increased, it emits thermal radiation, and its color changes because the radiation spectrum shifts towards shorter wavelengths:
1. When the temperature is lower, the substance emits infrared radiation, which is not visible.
2. With increasing temperature, it begins to emit red light which is the first coloured light.
3. The glow now becomes yellow with further heating and eventually goes white when the emitted light ranges over a bigger spectrum, covering the whole visible wavelengths.
This happens to be due to blackbody radiation and Planck’s law in which higher temperatures correspond to higher-energy radiation while, at the same time, there is a shift in the emission spectrum.
Click here:
See lesshttps://www.tiwariacademy.com/ncert-solutions/class-11/physics/chapter-10/
State and illustrate When’s displacement law. Give its importance.
Wien's Displacement Law states that the wavelength (λ_max) at which the intensity of radiation emitted by a black body is maximum is inversely proportional to its absolute temperature (T). In other words, as the temperature of the black body increases, the wavelength at which it emits the most radiaRead more
Wien’s Displacement Law states that the wavelength (λ_max) at which the intensity of radiation emitted by a black body is maximum is inversely proportional to its absolute temperature (T). In other words, as the temperature of the black body increases, the wavelength at which it emits the most radiation decreases.
Mathematically, Wien’s Displacement Law is given as:
λ_max = b / T
where:
– λ_max is the wavelength at which the emission intensity is maximum,
– T is the absolute temperature of the black body in Kelvin (K),
– b is Wien’s displacement constant, approximately 2.898 × 10⁻³ m·K.
Illustration:
– Object at 300 K: Using Wien’s Displacement Law, we calculate the wavelength where its radiation peaks.
λ_max = (2.898 × 10⁻³) / 300 = 9.66 μm
This is in the infrared region.
– Object at 600 K: The peak wavelength of emission is twice the object at 300 K since the temperature has an inverse proportionality to peak wavelength.
λ_max = (2.898 × 10⁻³) / 600 = 4.83 μm
It is still within the infrared, but shorter now.
Relevance of Wien’s Displacement Law:
1. Temperature Determination from Radiation:
Temperature of any object could be determined by the peak wavelength of emitted radiation under the law. It finds many applications in astrophysics, for example, to estimate the temperature of stars as a function of the color of stars. Therefore, it gives a color equivalent estimation.
2. Color of Stars
According to Wien’s law, hotter stars emit more radiation at shorter wavelengths, causing them to appear bluer, and cooler stars emit at longer wavelengths, making them appear redder.
3. Thermal Radiation Understanding:
Wien’s law helps us understand the nature of thermal radiation and how temperature affects the radiation emitted by objects, which is vital in many fields, including climatology and energy studies.
4. Temperature Measurement Applications: The law is applied in infrared thermometry, which allows objects to be measured for temperature without direct contact. This is found in industrial, medical, and scientific applications.
Click here:
See lesshttps://www.tiwariacademy.com/ncert-solutions/class-11/physics/chapter-10/