Thermal convection involves the transfer of heat through the movement of the fluid itself and is achieved based on the dissimilarity of temperature within that fluid, a liquid or a gas. Thermal convection current is established, as warmer locations of the fluid become less heavy and rise above, wherRead more
Thermal convection involves the transfer of heat through the movement of the fluid itself and is achieved based on the dissimilarity of temperature within that fluid, a liquid or a gas. Thermal convection current is established, as warmer locations of the fluid become less heavy and rise above, whereas more cold regions grow denser than the rest part of the fluid and move downward inside the fluid medium.
Convection currents in water are set up when there is a temperature difference within the water. Here’s how it happens:
1. Heating: When the bottom of a container of water is heated, the water near the heat source becomes warmer. As it heats up, the water molecules move faster and spread apart, reducing the water’s density.
2. Rising of Warm Water: The less dense warm water rises to the surface.
3. Cooling at the Surface: Once the warm water hits the surface, it cools because the heat is transferred to the surroundings. The cooling densefies the water in the container.
4. Sinking of Cool Water: The denser and cooler water sinks to the bottom of the container.
5. Circulatory Flow Development: This ongoing circulation of warm rising water and sinking cool water generates convection currents that assist in the equalizing of heat over the water body.
Natural vs. Forced Convection
– Natural Convection:
– Natural convection arises based on the intrinsic density differences present in a fluid due to variations in temperature.
– As warm fluid becomes lighter and rises, the cold fluid sinks, establishing a natural convection without needing an external source.
-Example: the circulation of currents in the air, ocean circulation, or the convection of liquid in the earth
-Forced Convection
– Forced convection occurs when there is an application of an external force such as a fan or pump to stir the fluid in order to promote heat transfer.
The movement of the fluid is not because of temperature gradients but is forced upon it by means of an external agent.
Example: water being pumped through a radiator to dissipate heat or air forcibly passed over a heat sink in an electronic device.
A black body is an idealized physical object which absorbs all the electromagnetic radiation or light falling upon it, with no regard to frequency or angle of incidence. It also radiates electromagnetic waves with a spectrum that depends solely on its temperature, and it is known as black body radiaRead more
A black body is an idealized physical object which absorbs all the electromagnetic radiation or light falling upon it, with no regard to frequency or angle of incidence. It also radiates electromagnetic waves with a spectrum that depends solely on its temperature, and it is known as black body radiation.
Realization in Practice:
– A perfect black body cannot be constructed physically, but approximate versions can be built.
– A cavity with a small hole can be considered to be a black body. The radiation entering the hole bounces several times within the cavity and is absorbed by the walls. The hole provides an opening for the radiation to escape, and the radiation that escapes closely mimics black body radiation.
– Materials such as lampblack or charcoal absorb a large amount of radiation and may be used as good approximations for a black body in experiments.
Absorptive Power (A): It is that fraction of the total incident radiation that a body absorbs. It is defined as the ratio of the energy absorbed by the body to the total energy incident on it. A = (Energy absorbed) / (Total incident energy) Emissive Power (E): It is that amount of energy radiateRead more
Absorptive Power (A):
It is that fraction of the total incident radiation that a body absorbs. It is defined as the ratio of the energy absorbed by the body to the total energy incident on it.
A = (Energy absorbed) / (Total incident energy)
Emissive Power (E):
It is that amount of energy radiated per unit area by a body per unit time at some temperature. Its value depends upon the nature of the material as well as upon its temperature.
E = Energy emitted/area × Time
Emissivity (e):
It is the ratio of the emissive power of a body to the emissive power of a perfect black body at the same temperature. It varies between 0 and 1, with 1 being a perfect black body.
e = (E_body) / (E_black body)
Newton's Law of Cooling: Newton's law of cooling provides the rate at which the temperature of a body changes with respect to time in proportion to the difference between its temperature and ambient temperature, while the difference should not be significantly large. Mathematical Formulation: dT/dtRead more
Newton’s Law of Cooling: Newton’s law of cooling provides the rate at which the temperature of a body changes with respect to time in proportion to the difference between its temperature and ambient temperature, while the difference should not be significantly large.
Mathematical Formulation: dT/dt = -k(T-T∞) In the above relation: T – Temperature of body at time ‘t’ T∞ Ambient temperature or Temperature of surrounding media k Positive coefficient of proportionality (cooling constant)
– dT/dt = rate of change of temperature with respect to time
Experimentally Verification of Newton’s Law of Cooling:
1. Materials Required: Hot water, calorimeter, thermometer, stopwatch, and a controlled room for a stable ambient temperature.
2. Procedure:
– Heat water to a certain temperature.
– Pour it into a calorimeter and record the initial temperature T₀.
– Put the calorimeter in a room whose ambient temperature is kept constant at T∞.
– Use a thermometer to measure the water temperature at equal intervals of time and record the readings.
3. Observation:
– Plot a graph of ln(T – T∞) vs. time.
– If the graph is a straight line with a negative slope, it confirms the law.
4. Conclusion:
– The slope of the line will be negative and will be proportional to the cooling constant k.
This experiment verifies Newton’s law of cooling.
Electromagnetic waves are a mode of energy propagation that travel through space at the speed of light. They consist of oscillating electric and magnetic fields that are perpendicular to each other and to the direction of wave propagation. Electromagnetic waves range from radio waves, microwaves, inRead more
Electromagnetic waves are a mode of energy propagation that travel through space at the speed of light. They consist of oscillating electric and magnetic fields that are perpendicular to each other and to the direction of wave propagation. Electromagnetic waves range from radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays.
Key features of electromagnetic waves include:
1. Wavelength and Frequency:
– The wavelength is the distance between successive crests of the wave, while frequency refers to the number of oscillations per second. These two are inversely related by the equation c = λ * f, where c is the speed of light, λ is the wavelength, and f is the frequency.
2. Energy:
– The energy of an electromagnetic wave is directly proportional to its frequency, and inversely proportional to its wavelength as outlined by E = h * f, where E is energy, h is Planck’s constant, and f is the frequency.
Thermal Radiation vs. Light:
Thermal radiation and visible light are two electromagnetic radiations, yet they are distinct in the following ways:
1. Wavelength and Frequency:
– Thermal radiation is mostly infrared, with longer wavelengths than visible light. The wavelengths of thermal radiation range from about 0.7 micrometers to 1 millimeter.
– Visible light has wavelengths between 400 and 700 nanometers, which are much shorter than thermal radiation.
2. Source:
– All objects emit thermal radiation according to their temperature. The hotter an object is, the more thermal radiation it emits, and it usually radiates in the infrared spectrum.
– Light is emitted by sources such as the Sun, light bulbs, or other artificial sources, and it mainly involves wavelengths in the visible spectrum.
3. Temperature Dependence:
– Thermal radiation increases with the temperature of an object, as described by Planck’s law and the Stefan-Boltzmann law. For instance, objects at higher temperatures emit more radiation at shorter wavelengths (like visible light) and at higher intensities.
The intensity of visible light is not necessarily related to the temperature of the object, in that it is produced by some processes that do not depend on temperature, for example, by emission from atoms and molecules.
Summary
– Thermal radiation is that infrared radiation due to the temperature of an object.
– Light is the portion of the electromagnetic spectrum that the human eye is sensitive to, which is commonly referred to as visible light.
What is thermal convection? Briefly explain how are convection currents set up in water? Distinguish between natural and forced convections.
Thermal convection involves the transfer of heat through the movement of the fluid itself and is achieved based on the dissimilarity of temperature within that fluid, a liquid or a gas. Thermal convection current is established, as warmer locations of the fluid become less heavy and rise above, wherRead more
Thermal convection involves the transfer of heat through the movement of the fluid itself and is achieved based on the dissimilarity of temperature within that fluid, a liquid or a gas. Thermal convection current is established, as warmer locations of the fluid become less heavy and rise above, whereas more cold regions grow denser than the rest part of the fluid and move downward inside the fluid medium.
Convection currents in water are set up when there is a temperature difference within the water. Here’s how it happens:
1. Heating: When the bottom of a container of water is heated, the water near the heat source becomes warmer. As it heats up, the water molecules move faster and spread apart, reducing the water’s density.
2. Rising of Warm Water: The less dense warm water rises to the surface.
3. Cooling at the Surface: Once the warm water hits the surface, it cools because the heat is transferred to the surroundings. The cooling densefies the water in the container.
4. Sinking of Cool Water: The denser and cooler water sinks to the bottom of the container.
5. Circulatory Flow Development: This ongoing circulation of warm rising water and sinking cool water generates convection currents that assist in the equalizing of heat over the water body.
Natural vs. Forced Convection
– Natural Convection:
– Natural convection arises based on the intrinsic density differences present in a fluid due to variations in temperature.
– As warm fluid becomes lighter and rises, the cold fluid sinks, establishing a natural convection without needing an external source.
-Example: the circulation of currents in the air, ocean circulation, or the convection of liquid in the earth
-Forced Convection
– Forced convection occurs when there is an application of an external force such as a fan or pump to stir the fluid in order to promote heat transfer.
The movement of the fluid is not because of temperature gradients but is forced upon it by means of an external agent.
Example: water being pumped through a radiator to dissipate heat or air forcibly passed over a heat sink in an electronic device.
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What is a black body? How can it be realised in practice?
A black body is an idealized physical object which absorbs all the electromagnetic radiation or light falling upon it, with no regard to frequency or angle of incidence. It also radiates electromagnetic waves with a spectrum that depends solely on its temperature, and it is known as black body radiaRead more
A black body is an idealized physical object which absorbs all the electromagnetic radiation or light falling upon it, with no regard to frequency or angle of incidence. It also radiates electromagnetic waves with a spectrum that depends solely on its temperature, and it is known as black body radiation.
Realization in Practice:
– A perfect black body cannot be constructed physically, but approximate versions can be built.
– A cavity with a small hole can be considered to be a black body. The radiation entering the hole bounces several times within the cavity and is absorbed by the walls. The hole provides an opening for the radiation to escape, and the radiation that escapes closely mimics black body radiation.
– Materials such as lampblack or charcoal absorb a large amount of radiation and may be used as good approximations for a black body in experiments.
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See lesshttps://www.tiwariacademy.com/ncert-solutions/class-11/physics/chapter-10/
Define the terms absorptive power, emissive power and emissivity.
Absorptive Power (A): It is that fraction of the total incident radiation that a body absorbs. It is defined as the ratio of the energy absorbed by the body to the total energy incident on it. A = (Energy absorbed) / (Total incident energy) Emissive Power (E): It is that amount of energy radiateRead more
Absorptive Power (A):
It is that fraction of the total incident radiation that a body absorbs. It is defined as the ratio of the energy absorbed by the body to the total energy incident on it.
A = (Energy absorbed) / (Total incident energy)
Emissive Power (E):
It is that amount of energy radiated per unit area by a body per unit time at some temperature. Its value depends upon the nature of the material as well as upon its temperature.
E = Energy emitted/area × Time
Emissivity (e):
It is the ratio of the emissive power of a body to the emissive power of a perfect black body at the same temperature. It varies between 0 and 1, with 1 being a perfect black body.
e = (E_body) / (E_black body)
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State Newton’s law of cooling. Express it mathematically. How can this law be verified experimentally?
Newton's Law of Cooling: Newton's law of cooling provides the rate at which the temperature of a body changes with respect to time in proportion to the difference between its temperature and ambient temperature, while the difference should not be significantly large. Mathematical Formulation: dT/dtRead more
Newton’s Law of Cooling: Newton’s law of cooling provides the rate at which the temperature of a body changes with respect to time in proportion to the difference between its temperature and ambient temperature, while the difference should not be significantly large.
Mathematical Formulation: dT/dt = -k(T-T∞) In the above relation: T – Temperature of body at time ‘t’ T∞ Ambient temperature or Temperature of surrounding media k Positive coefficient of proportionality (cooling constant)
– dT/dt = rate of change of temperature with respect to time
Experimentally Verification of Newton’s Law of Cooling:
1. Materials Required: Hot water, calorimeter, thermometer, stopwatch, and a controlled room for a stable ambient temperature.
2. Procedure:
– Heat water to a certain temperature.
– Pour it into a calorimeter and record the initial temperature T₀.
– Put the calorimeter in a room whose ambient temperature is kept constant at T∞.
– Use a thermometer to measure the water temperature at equal intervals of time and record the readings.
3. Observation:
– Plot a graph of ln(T – T∞) vs. time.
– If the graph is a straight line with a negative slope, it confirms the law.
4. Conclusion:
– The slope of the line will be negative and will be proportional to the cooling constant k.
This experiment verifies Newton’s law of cooling.
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What are electromagnetic waves? In what respect is the thermal radiation different from light?
Electromagnetic waves are a mode of energy propagation that travel through space at the speed of light. They consist of oscillating electric and magnetic fields that are perpendicular to each other and to the direction of wave propagation. Electromagnetic waves range from radio waves, microwaves, inRead more
Electromagnetic waves are a mode of energy propagation that travel through space at the speed of light. They consist of oscillating electric and magnetic fields that are perpendicular to each other and to the direction of wave propagation. Electromagnetic waves range from radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays.
Key features of electromagnetic waves include:
1. Wavelength and Frequency:
– The wavelength is the distance between successive crests of the wave, while frequency refers to the number of oscillations per second. These two are inversely related by the equation c = λ * f, where c is the speed of light, λ is the wavelength, and f is the frequency.
2. Energy:
– The energy of an electromagnetic wave is directly proportional to its frequency, and inversely proportional to its wavelength as outlined by E = h * f, where E is energy, h is Planck’s constant, and f is the frequency.
Thermal Radiation vs. Light:
Thermal radiation and visible light are two electromagnetic radiations, yet they are distinct in the following ways:
1. Wavelength and Frequency:
– Thermal radiation is mostly infrared, with longer wavelengths than visible light. The wavelengths of thermal radiation range from about 0.7 micrometers to 1 millimeter.
– Visible light has wavelengths between 400 and 700 nanometers, which are much shorter than thermal radiation.
2. Source:
– All objects emit thermal radiation according to their temperature. The hotter an object is, the more thermal radiation it emits, and it usually radiates in the infrared spectrum.
– Light is emitted by sources such as the Sun, light bulbs, or other artificial sources, and it mainly involves wavelengths in the visible spectrum.
3. Temperature Dependence:
– Thermal radiation increases with the temperature of an object, as described by Planck’s law and the Stefan-Boltzmann law. For instance, objects at higher temperatures emit more radiation at shorter wavelengths (like visible light) and at higher intensities.
The intensity of visible light is not necessarily related to the temperature of the object, in that it is produced by some processes that do not depend on temperature, for example, by emission from atoms and molecules.
Summary
– Thermal radiation is that infrared radiation due to the temperature of an object.
– Light is the portion of the electromagnetic spectrum that the human eye is sensitive to, which is commonly referred to as visible light.
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See lesshttps://www.tiwariacademy.com/ncert-solutions/class-11/physics/chapter-10/