Variable State in Thermal Conduction In thermal conduction, a variable state refers to a situation where the temperature distribution within the material is changing with time. In this state, the temperature at any point in the material is not constant, and the heat flow is not steady. This usuallyRead more
Variable State in Thermal Conduction
In thermal conduction, a variable state refers to a situation where the temperature distribution within the material is changing with time. In this state, the temperature at any point in the material is not constant, and the heat flow is not steady. This usually occurs when the material is initially heated or cooled, and the temperature difference between different parts of the material is evolving over time until it reaches equilibrium.
– For instance, suppose a metal rod is heated on one end; the temperature changes at different points along the rod with time since heat is being transferred from the hot end to the cooler end. The gradient will be high in the beginning, and with the passage of time, the gradient will decrease to the point when the system achieves equilibrium.
Steady State in Thermal Conduction:
In thermal conduction, a steady state is when the temperature distribution in the material becomes constant over time. The temperature at any point in the material no longer changes, which means there is no further change in temperature with respect to time. The heat flow becomes constant, and the system has reached thermal equilibrium.
Example: For instance, if the temperature has stabilized such that no temperature variation is noticed in the rod as described earlier, then the system is in a steady state. The amount of heat going into one end is the same as the amount of heat going out the other end.
Temperature Gradient:
Temperature gradient is the measure of how temperature changes over a given distance in a material. It is defined as the rate of change of temperature with respect to distance. It is often measured in units of °C/m or K/m.
– Mathematical Expression: The temperature gradient ∇T can be mathematically expressed as:
∇T = ΔT / Δx
Where:
– ∇T = Temperature gradient (°C/m or K/m)
– ΔT = Temperature difference between two points in the material (°C or K)
– Δx = Distance between the two points (m)
In a steady-state conduction, the temperature gradient is constant and linear, so that the rate of temperature change is uniform throughout the material. In a variable state, the temperature gradient changes with time as the material approaches a new thermal equilibrium.
Effect of Pressure on the Boiling Point of a Liquid: The boiling point of a liquid is that temperature at which its vapor pressure becomes equal to the external pressure acting on it. When the pressure is increased, the boiling point of the liquid also increases, and when the pressure is decreased,Read more
Effect of Pressure on the Boiling Point of a Liquid:
The boiling point of a liquid is that temperature at which its vapor pressure becomes equal to the external pressure acting on it. When the pressure is increased, the boiling point of the liquid also increases, and when the pressure is decreased, the boiling point decreases. This is because a high pressure requires much energy (heat) to enable the liquid molecules to escape into the vapor phase, while a low pressure will make it easier to vaporize.
Explanation Using a Simple Experiment
To understand how pressure affects the boiling point of a liquid, you can perform a simple experiment using a saucepan, a thermometer, and a vacuum pump or a simple setup to create a change in pressure.
Experiment:
1. Materials Needed:
– A saucepan or beaker
– A thermometer
– A vacuum pump (for lowering pressure) or a pressure cooker (for increasing pressure)
– Water or another liquid (such as alcohol)
2. Procedures:
Experiment 1 (Effect of Decreasing Pressure):
1. Put water in the saucepan and place it on a heat source.
2. Dip the thermometer into the water and measure the temperature.
3. Boil the water and note the temperature at which it starts boiling. The boiling point of water at atmospheric pressure is usually about 100°C.
4. Reduce the pressure using a vacuum pump. Alternatively, you can do this in a simple vacuum chamber, if available.
5. Notice that the water starts boiling at a temperature less than 100°C as the pressure is reduced.
Experiment 2: Effect of Increasing Pressure
1. Repeat the same setup but use a pressure cooker instead of the open saucepan.
2. When the pressure cooker is sealed, it increases the pressure inside.
3. You will notice that as the pressure is increased, it takes longer for the water to boil, and the boiling point is above 100°C.
3. Observations:
– In Experiment 1, as the pressure inside the chamber decreases, the water boils at a temperature lower than its normal boiling point (100°C at 1 atmosphere).
In Experiment 2, the higher temperature at which the water boils results from the increased pressure inside the pressure cooker.
Explanation in Science Terms:
At Low Pressure: Fewer air molecules exert force on the liquid’s surface when pressure is low, so it’s easier for liquid molecules to go into the vapor phase. In this case, the liquid will boil at a lower temperature. That is why water boils at a lower temperature at high altitude where the pressure of the atmosphere is low.
– At Higher Pressure: When the pressure is increased (like in a pressure cooker), the liquid’s vapor pressure needs to overcome a higher external pressure to escape into the gas phase. Therefore, the liquid boils at a higher temperature to provide the necessary energy for the molecules to break free from the liquid phase.
A change of state is the transformation of a substance from one physical phase or state of matter to another. The three most common states of matter are solid, liquid, and gas. A substance can change between these states due to the addition or removal of heat energy. The change of state involves chaRead more
A change of state is the transformation of a substance from one physical phase or state of matter to another. The three most common states of matter are solid, liquid, and gas. A substance can change between these states due to the addition or removal of heat energy. The change of state involves changes in the arrangement and energy of the particles (atoms or molecules) that make up the substance.
Types of Changes of State:
1. Melting (Solid to Liquid):
– When the solid is heated, the energy of the particles increases, causing them to move more freely until they break away from each other. The end result is the solid turns to liquid.
Example: Ice turns to water due to melting.
2. Freezing (Liquid to Solid):
– When a liquid is cooled, the particles lose energy and move slowly; thus, they can form bonds and arrange themselves in an orderly structure to make the liquid become a solid.
Example: Water freezes to ice.
3. Vaporization (Liquid to Gas):
This happens when a liquid is heated; the particles receive enough energy so that they would be able to overcome the forces holding them in place, break free, and escape into the gas phase by vaporization. Included in this are evaporation through the surface of a liquid at any temperature, and boiling that occurs throughout a liquid at specific temperatures. Example: boiling water into steam.
4. Condensation from Gas to Liquid
– When a gas is cooled, the particles lose energy, slow down, and come closer together, forming liquid droplets.
Example: Water vapor condensing on a cold surface.
5. Sublimation (Solid to Gas):
– Change of phase from solid directly to gas, bypassing the liquid phase. This takes place when the solid particles acquire sufficient energy to break free from their bonds, dispersing themselves as gas particles.
– Dry ice is the solid carbon dioxide sublimating to carbon dioxide gas.
6. Deposition (Gas to Solid):
– Deposition is the opposite of sublimation, where a gas transforms directly into a solid without going through the liquid phase. This happens when gas particles lose enough energy to settle into a solid structure.
Example: Frost forming from water vapor in the air.
Factors Affecting the Change of State:
– Temperature: The addition of heat energy raises the temperature, and the substance can change from solid to liquid or from liquid to gas, such as melting or vaporization. Cooling the substance will cause the opposite changes, like freezing or condensation.
Pressure applied to a substance can also be a variable. For example, increasing the pressure can make a gas condense into a liquid or even a liquid freeze into a solid.
Calorimetry is the science and technique of measuring heat transfer in chemical reactions and changes of state or heat capacity in substances. Calorimetry is the process used in quantifying the heat absorbed or released in a reaction or phase change - typically using an apparatus known as a calorimeRead more
Calorimetry is the science and technique of measuring heat transfer in chemical reactions and changes of state or heat capacity in substances. Calorimetry is the process used in quantifying the heat absorbed or released in a reaction or phase change – typically using an apparatus known as a calorimeter.
Calorimetry Principle:
The principle of calorimetry is based on the law of conservation of energy, which states that energy cannot be created or destroyed, only transformed from one form to another. In calorimetry, the heat lost or gained by the system is equal to the heat gained or lost by the surroundings (if isolated), and this heat change is measured.
Mathematically, it can be expressed as:
Qₗₒₛₜ = Q₉ₐᵢₙₑₔ
Where:
– Qₗₒₛₜ is the heat energy lost by the hot object (or substance),
– Q₉ₐᵢₙₑₔ is the heat energy gained by the cold object (or surroundings).
In calorimetry, the amount of energy change or heat flow is usually determined from the degree of temperature change in a measured mass of the substance, using the formula:
Q = mcΔT
Where:
– Q = Heat energy absorbed or released (in joules, J),
– m = Mass of the substance (in kilograms or grams),
– c = Specific heat capacity of the substance (in J/kg·°C or J/g·°C),
– ΔT = Change in temperature (in °C or K).
1. Electrical Wiring and Cables Application: In terms of designing and utilizing electrical wiring and cables, the application of electrical conductivity is vital. The key materials that are used are copper and aluminum due to their high electrical conductivity. Electricity flows smoothly from the pRead more
1. Electrical Wiring and Cables
Application: In terms of designing and utilizing electrical wiring and cables, the application of electrical conductivity is vital. The key materials that are used are copper and aluminum due to their high electrical conductivity. Electricity flows smoothly from the power source to the homes, devices, and appliances through these materials.
– Example: House electrical wiring, transmission lines for electricity, and electronic device chargers.
2. Heating Elements (Electric Heaters)
– Application: In electric heating elements, a material’s resistance generates heat as an electric current passes through it. This is the reason for using this property in appliances such as toasters, electric ovens, and space heaters.
– Example: The metal wires in a toaster that heat up and toast bread due to their resistance to the flow of electricity.
3. Thermometers (Thermal Conductivity)
– Application: Thermal conductivity is used in thermometers, especially liquid-in-glass thermometers, such as mercury or alcohol thermometers, in which the rate of temperature change affects the liquid inside. Materials with high thermal conductivity, such as metals, are used in heat sensors to detect temperatures accurately.
Example: Metal thermometers used in cooking or industries that rely on fast heat transfer.
4. Electronics Heat Sinks
Application: Copper and aluminum are examples of high thermal conductivity materials, used in heat sinks to avoid overheating of electronic devices such as computers and mobile phones. They absorb and dissipate heat effectively from sensitive components such as processors.
Example: Cooling systems in computers, graphics cards, and power supplies.
5. Battery Technology
– Usage: Electrical conductivity plays a critical role in the construction of batteries. Highly conductive materials are applied in the electrodes and electrolytes of rechargeable batteries such as lithium-ion batteries. They enable effective charging and discharging cycles in applications like smartphones, laptops, and electric vehicles.
-Example: The conducting material in the battery of a smartphone or electric car.
6. Conductive Textiles and Garments
– Application: Conductive materials are used in fabrics for various applications, such as wearable electronics, touch-sensitive clothing, and heated clothing. These fabrics can conduct electricity, allowing them to work with sensors, LED lights, or heating elements embedded in the fabric.
Example: Touchscreen gloves, heated jackets, and smart clothing with embedded sensors.
7. Cooking Utensils (Thermal Conductivity)
– Application: The materials applied for cookware have high thermal conductivity, like copper or aluminum. These materials facilitate the uniform spreading of heat throughout the surface and enhance cooking efficiency.
Example: Copper or aluminum pots, pans, and frying pans.
8. Water Treatment (Conductivity Sensors)
– Application: It is applied in water treatment and quality monitoring. The conductivity sensors are used to determine the level of dissolved solids in water, thus determining its purity and quality. It is applied both in industrial processes and household filtration systems.
Example: Filtration systems that monitor the quality of drinking water.
9. Electroplating
– Application: Conductivity is of utmost importance in electroplating, where an electric current coats metals onto objects’ surfaces. This process makes use of the movement of electricity throughout the material for the deposition of a thin metal layer.
– Example: Gold or silver plating for jewelry, coins, and any other decorative article.
10. Smartphones and Touchscreen Technology
– Application: Conductivity is used in touchscreens of mobile phones, tablets, and other devices. Capacitive touchscreens depend on the conductivity of the human finger to sense touch inputs.
Example: Touchscreen smartphones that respond to finger taps due to the conductivity of the human skin.
11. Electrolysis (Water Splitting)
– Application: Conductivity is applied in electrolysis, in which an electrical current is passed through water to split it into hydrogen and oxygen gases. The process is involved in hydrogen production for fuel cells or industrial purposes.
– Example: Water electrolysis systems used in laboratories or for hydrogen fuel production.
12. Conductive Adhesives and Paints
– Application: In electronic circuits and devices where the use of traditional wiring is impractical, conductive adhesives and paints work by allowing electrical currents to flow through surfaces bonded together.
Examples: Printed circuit boards (PCBs) and flexible electronics work with conductive inks for connections.
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 do you mean by variable state and steady state in thermal conduction? Define temperature gradient.
Variable State in Thermal Conduction In thermal conduction, a variable state refers to a situation where the temperature distribution within the material is changing with time. In this state, the temperature at any point in the material is not constant, and the heat flow is not steady. This usuallyRead more
Variable State in Thermal Conduction
In thermal conduction, a variable state refers to a situation where the temperature distribution within the material is changing with time. In this state, the temperature at any point in the material is not constant, and the heat flow is not steady. This usually occurs when the material is initially heated or cooled, and the temperature difference between different parts of the material is evolving over time until it reaches equilibrium.
– For instance, suppose a metal rod is heated on one end; the temperature changes at different points along the rod with time since heat is being transferred from the hot end to the cooler end. The gradient will be high in the beginning, and with the passage of time, the gradient will decrease to the point when the system achieves equilibrium.
Steady State in Thermal Conduction:
In thermal conduction, a steady state is when the temperature distribution in the material becomes constant over time. The temperature at any point in the material no longer changes, which means there is no further change in temperature with respect to time. The heat flow becomes constant, and the system has reached thermal equilibrium.
Example: For instance, if the temperature has stabilized such that no temperature variation is noticed in the rod as described earlier, then the system is in a steady state. The amount of heat going into one end is the same as the amount of heat going out the other end.
Temperature Gradient:
Temperature gradient is the measure of how temperature changes over a given distance in a material. It is defined as the rate of change of temperature with respect to distance. It is often measured in units of °C/m or K/m.
– Mathematical Expression: The temperature gradient ∇T can be mathematically expressed as:
∇T = ΔT / Δx
Where:
– ∇T = Temperature gradient (°C/m or K/m)
– ΔT = Temperature difference between two points in the material (°C or K)
– Δx = Distance between the two points (m)
In a steady-state conduction, the temperature gradient is constant and linear, so that the rate of temperature change is uniform throughout the material. In a variable state, the temperature gradient changes with time as the material approaches a new thermal equilibrium.
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What is the effect of pressure on the boiling point of a liquid. Explain it with the help of a simple experiment.
Effect of Pressure on the Boiling Point of a Liquid: The boiling point of a liquid is that temperature at which its vapor pressure becomes equal to the external pressure acting on it. When the pressure is increased, the boiling point of the liquid also increases, and when the pressure is decreased,Read more
Effect of Pressure on the Boiling Point of a Liquid:
The boiling point of a liquid is that temperature at which its vapor pressure becomes equal to the external pressure acting on it. When the pressure is increased, the boiling point of the liquid also increases, and when the pressure is decreased, the boiling point decreases. This is because a high pressure requires much energy (heat) to enable the liquid molecules to escape into the vapor phase, while a low pressure will make it easier to vaporize.
Explanation Using a Simple Experiment
To understand how pressure affects the boiling point of a liquid, you can perform a simple experiment using a saucepan, a thermometer, and a vacuum pump or a simple setup to create a change in pressure.
Experiment:
1. Materials Needed:
– A saucepan or beaker
– A thermometer
– A vacuum pump (for lowering pressure) or a pressure cooker (for increasing pressure)
– Water or another liquid (such as alcohol)
2. Procedures:
Experiment 1 (Effect of Decreasing Pressure):
1. Put water in the saucepan and place it on a heat source.
2. Dip the thermometer into the water and measure the temperature.
3. Boil the water and note the temperature at which it starts boiling. The boiling point of water at atmospheric pressure is usually about 100°C.
4. Reduce the pressure using a vacuum pump. Alternatively, you can do this in a simple vacuum chamber, if available.
5. Notice that the water starts boiling at a temperature less than 100°C as the pressure is reduced.
Experiment 2: Effect of Increasing Pressure
1. Repeat the same setup but use a pressure cooker instead of the open saucepan.
2. When the pressure cooker is sealed, it increases the pressure inside.
3. You will notice that as the pressure is increased, it takes longer for the water to boil, and the boiling point is above 100°C.
3. Observations:
– In Experiment 1, as the pressure inside the chamber decreases, the water boils at a temperature lower than its normal boiling point (100°C at 1 atmosphere).
In Experiment 2, the higher temperature at which the water boils results from the increased pressure inside the pressure cooker.
Explanation in Science Terms:
At Low Pressure: Fewer air molecules exert force on the liquid’s surface when pressure is low, so it’s easier for liquid molecules to go into the vapor phase. In this case, the liquid will boil at a lower temperature. That is why water boils at a lower temperature at high altitude where the pressure of the atmosphere is low.
– At Higher Pressure: When the pressure is increased (like in a pressure cooker), the liquid’s vapor pressure needs to overcome a higher external pressure to escape into the gas phase. Therefore, the liquid boils at a higher temperature to provide the necessary energy for the molecules to break free from the liquid phase.
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What do you mean by change of state of a substance?
A change of state is the transformation of a substance from one physical phase or state of matter to another. The three most common states of matter are solid, liquid, and gas. A substance can change between these states due to the addition or removal of heat energy. The change of state involves chaRead more
A change of state is the transformation of a substance from one physical phase or state of matter to another. The three most common states of matter are solid, liquid, and gas. A substance can change between these states due to the addition or removal of heat energy. The change of state involves changes in the arrangement and energy of the particles (atoms or molecules) that make up the substance.
Types of Changes of State:
1. Melting (Solid to Liquid):
– When the solid is heated, the energy of the particles increases, causing them to move more freely until they break away from each other. The end result is the solid turns to liquid.
Example: Ice turns to water due to melting.
2. Freezing (Liquid to Solid):
– When a liquid is cooled, the particles lose energy and move slowly; thus, they can form bonds and arrange themselves in an orderly structure to make the liquid become a solid.
Example: Water freezes to ice.
3. Vaporization (Liquid to Gas):
This happens when a liquid is heated; the particles receive enough energy so that they would be able to overcome the forces holding them in place, break free, and escape into the gas phase by vaporization. Included in this are evaporation through the surface of a liquid at any temperature, and boiling that occurs throughout a liquid at specific temperatures. Example: boiling water into steam.
4. Condensation from Gas to Liquid
– When a gas is cooled, the particles lose energy, slow down, and come closer together, forming liquid droplets.
Example: Water vapor condensing on a cold surface.
5. Sublimation (Solid to Gas):
– Change of phase from solid directly to gas, bypassing the liquid phase. This takes place when the solid particles acquire sufficient energy to break free from their bonds, dispersing themselves as gas particles.
– Dry ice is the solid carbon dioxide sublimating to carbon dioxide gas.
6. Deposition (Gas to Solid):
– Deposition is the opposite of sublimation, where a gas transforms directly into a solid without going through the liquid phase. This happens when gas particles lose enough energy to settle into a solid structure.
Example: Frost forming from water vapor in the air.
Factors Affecting the Change of State:
– Temperature: The addition of heat energy raises the temperature, and the substance can change from solid to liquid or from liquid to gas, such as melting or vaporization. Cooling the substance will cause the opposite changes, like freezing or condensation.
Pressure applied to a substance can also be a variable. For example, increasing the pressure can make a gas condense into a liquid or even a liquid freeze into a solid.
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What is calorimetry? State the principle of calorimetry.
Calorimetry is the science and technique of measuring heat transfer in chemical reactions and changes of state or heat capacity in substances. Calorimetry is the process used in quantifying the heat absorbed or released in a reaction or phase change - typically using an apparatus known as a calorimeRead more
Calorimetry is the science and technique of measuring heat transfer in chemical reactions and changes of state or heat capacity in substances. Calorimetry is the process used in quantifying the heat absorbed or released in a reaction or phase change – typically using an apparatus known as a calorimeter.
Calorimetry Principle:
The principle of calorimetry is based on the law of conservation of energy, which states that energy cannot be created or destroyed, only transformed from one form to another. In calorimetry, the heat lost or gained by the system is equal to the heat gained or lost by the surroundings (if isolated), and this heat change is measured.
Mathematically, it can be expressed as:
Qₗₒₛₜ = Q₉ₐᵢₙₑₔ
Where:
– Qₗₒₛₜ is the heat energy lost by the hot object (or substance),
– Q₉ₐᵢₙₑₔ is the heat energy gained by the cold object (or surroundings).
In calorimetry, the amount of energy change or heat flow is usually determined from the degree of temperature change in a measured mass of the substance, using the formula:
Q = mcΔT
Where:
– Q = Heat energy absorbed or released (in joules, J),
– m = Mass of the substance (in kilograms or grams),
– c = Specific heat capacity of the substance (in J/kg·°C or J/g·°C),
– ΔT = Change in temperature (in °C or K).
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Describe some applications of conductivity in daily life.
1. Electrical Wiring and Cables Application: In terms of designing and utilizing electrical wiring and cables, the application of electrical conductivity is vital. The key materials that are used are copper and aluminum due to their high electrical conductivity. Electricity flows smoothly from the pRead more
1. Electrical Wiring and Cables
Application: In terms of designing and utilizing electrical wiring and cables, the application of electrical conductivity is vital. The key materials that are used are copper and aluminum due to their high electrical conductivity. Electricity flows smoothly from the power source to the homes, devices, and appliances through these materials.
– Example: House electrical wiring, transmission lines for electricity, and electronic device chargers.
2. Heating Elements (Electric Heaters)
– Application: In electric heating elements, a material’s resistance generates heat as an electric current passes through it. This is the reason for using this property in appliances such as toasters, electric ovens, and space heaters.
– Example: The metal wires in a toaster that heat up and toast bread due to their resistance to the flow of electricity.
3. Thermometers (Thermal Conductivity)
– Application: Thermal conductivity is used in thermometers, especially liquid-in-glass thermometers, such as mercury or alcohol thermometers, in which the rate of temperature change affects the liquid inside. Materials with high thermal conductivity, such as metals, are used in heat sensors to detect temperatures accurately.
Example: Metal thermometers used in cooking or industries that rely on fast heat transfer.
4. Electronics Heat Sinks
Application: Copper and aluminum are examples of high thermal conductivity materials, used in heat sinks to avoid overheating of electronic devices such as computers and mobile phones. They absorb and dissipate heat effectively from sensitive components such as processors.
Example: Cooling systems in computers, graphics cards, and power supplies.
5. Battery Technology
– Usage: Electrical conductivity plays a critical role in the construction of batteries. Highly conductive materials are applied in the electrodes and electrolytes of rechargeable batteries such as lithium-ion batteries. They enable effective charging and discharging cycles in applications like smartphones, laptops, and electric vehicles.
-Example: The conducting material in the battery of a smartphone or electric car.
6. Conductive Textiles and Garments
– Application: Conductive materials are used in fabrics for various applications, such as wearable electronics, touch-sensitive clothing, and heated clothing. These fabrics can conduct electricity, allowing them to work with sensors, LED lights, or heating elements embedded in the fabric.
Example: Touchscreen gloves, heated jackets, and smart clothing with embedded sensors.
7. Cooking Utensils (Thermal Conductivity)
– Application: The materials applied for cookware have high thermal conductivity, like copper or aluminum. These materials facilitate the uniform spreading of heat throughout the surface and enhance cooking efficiency.
Example: Copper or aluminum pots, pans, and frying pans.
8. Water Treatment (Conductivity Sensors)
– Application: It is applied in water treatment and quality monitoring. The conductivity sensors are used to determine the level of dissolved solids in water, thus determining its purity and quality. It is applied both in industrial processes and household filtration systems.
Example: Filtration systems that monitor the quality of drinking water.
9. Electroplating
– Application: Conductivity is of utmost importance in electroplating, where an electric current coats metals onto objects’ surfaces. This process makes use of the movement of electricity throughout the material for the deposition of a thin metal layer.
– Example: Gold or silver plating for jewelry, coins, and any other decorative article.
10. Smartphones and Touchscreen Technology
– Application: Conductivity is used in touchscreens of mobile phones, tablets, and other devices. Capacitive touchscreens depend on the conductivity of the human finger to sense touch inputs.
Example: Touchscreen smartphones that respond to finger taps due to the conductivity of the human skin.
11. Electrolysis (Water Splitting)
– Application: Conductivity is applied in electrolysis, in which an electrical current is passed through water to split it into hydrogen and oxygen gases. The process is involved in hydrogen production for fuel cells or industrial purposes.
– Example: Water electrolysis systems used in laboratories or for hydrogen fuel production.
12. Conductive Adhesives and Paints
– Application: In electronic circuits and devices where the use of traditional wiring is impractical, conductive adhesives and paints work by allowing electrical currents to flow through surfaces bonded together.
Examples: Printed circuit boards (PCBs) and flexible electronics work with conductive inks for connections.
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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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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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