📋 Table of Contents
🔥 Introduction to Thermal Transformation
Chapter 11: Thermal Transformation explores how matter responds to heat energy through changes in temperature, state, and dimensions. This chapter covers fundamental concepts including specific heat capacity, latent heat, thermal expansion, evaporation, boiling, and phase changes. Understanding these thermal properties is essential for explaining everyday phenomena and technological applications.
Multiple Choice Questions (MCQs)
Heat causes metal atoms to vibrate more vigorously, increasing their average separation and causing expansion.
Water vapor in air condenses into liquid droplets when it contacts cold surfaces.
Deposition is the direct transition from gas to solid, like frost formation.
Water boils at 212°F on the Fahrenheit scale, which equals 100°C on Celsius scale.
Specific heat capacity measures energy needed to raise 1kg of substance by 1K.
Evaporation occurs only at the liquid surface where molecules can escape into vapor.
For isotropic solids, coefficient of volume expansion β equals approximately 3α.
At melting point, heat energy weakens intermolecular forces rather than increasing kinetic energy.
Q = m × L = 10g × 336 J/g = 3360 J
Wind removes saturated air from surface, allowing more evaporation.
Using α = β/3 = (9 × 10⁻⁷)/3 = 3 × 10⁻⁷ K⁻¹
Evaporation requires latent heat of vaporization to convert liquid to vapor.
Using mathematical relationship between real and apparent expansion coefficients.
"Latent" means hidden because this heat doesn't cause temperature change.
Constructed Response Questions
Q1. Look at these graphs for heating the ice, Energy (E)-time (t) graph shows that energy is being supplied to ice at constant rate to change it into liquid and finally into steam. While the temperature (T)-time (t) graph shows that change of temperature of ice and water during different stages.
First Horizontal Stage (Melting): At 0°C, all supplied energy breaks ice's crystalline structure into liquid water. This latent heat of fusion changes state without temperature increase.
Second Horizontal Stage (Boiling): At 100°C, energy separates water molecules into vapor. This latent heat of vaporization overcomes liquid bonds without raising temperature.
During Phase Changes: Energy breaks intermolecular bonds rather than increasing molecular kinetic energy, so temperature remains constant despite energy input.
During Heating: Energy increases molecular kinetic energy, causing temperature rise. The rate depends on substance's specific heat capacity in each phase.
Q2. A heater supplies energy at a constant rate to a 100 g of a substance. The variation with time of the temperature of the substance is shown in the figure. The substance is perfectly insulated from its surroundings. The power of the heater is 250 W.
b. What is melting and boiling point of the substance?
How long does it take to melt completely and how long does it take to vaporize from liquid state?
c. How much temperature increases in its liquid phase (x part of the graph)?
d. Calculate latent heat of vaporization of the substance?
Given: Mass = 100g = 0.1kg, Power = 250W
Melting Point: 0°C (from graph plateau)
Boiling Point: 30°C (from graph plateau)
Melting Time: 5 minutes = 300 seconds
Vaporization Time: 10 minutes = 600 seconds
Liquid Temperature Increase: 30°C - 0°C = 30°C
Latent Heat of Vaporization Calculation:
= 250 W × 600 s
= 150,000 J
L_v = Q/m = 150,000 J / 0.1 kg
= 1,500,000 J/kg
= 1.5 × 10⁶ J/kg
Short Answer Questions
Q1. Why do dew-drops form on leaves and grass in a spring morning?
💧 Dew Formation Process
Dew forms through condensation when surface temperatures drop overnight. As air cools, its capacity to hold moisture decreases. When temperature reaches dew point, excess water vapor condenses on cool surfaces like leaves and grass, forming dew drops.
This occurs frequently in spring due to clear nights and adequate moisture in air, creating perfect conditions for dew formation.
Q2. What is the effect of pressure and temperature variation on sublimation and deposition?
| Sublimation (Solid → Gas) | Deposition (Gas → Solid) |
|---|---|
| Favored by high temperature | Favored by low temperature |
| Favored by low pressure | Favored by high pressure |
| Examples: Dry ice, moth balls | Examples: Frost formation |
Q3. Why do vapors form on the handle and cylinder of a fire extinguisher when it is discharged?
🧯 Joule-Thomson Effect
When fire extinguisher discharges, compressed gas rapidly expands, causing temperature drop due to Joule-Thomson effect. This cooling condenses atmospheric moisture on cold surfaces, forming visible water vapor droplets.
The phenomenon demonstrates how rapid gas expansion creates cooling, similar to how refrigerators work.
Q4. How does sweating helps to cool our body down during exercise?
💦 Evaporative Cooling
Sweating cools through evaporation. As sweat evaporates from skin, it absorbs latent heat of vaporization from body, removing heat energy. This process maintains stable body temperature during physical exertion.
Increased blood flow to skin enhances sweat production and cooling efficiency during exercise.
Q5. Consider a piece of metal X initially at a temperature of 100°C. It is placed on a heater (which is providing heat at constant rate) until it reaches a final temperature of 400°C. The metal has a melting point of 250°C.
📈 Temperature-Time Graph Analysis
Metal X Graph: Linear increase (100°C→250°C), plateau at 250°C (melting), then linear increase (250°C→400°C)
Metal Y Comparison: Same initial and final slopes, but longer melting plateau due to higher latent heat of fusion requiring more energy at same melting point.
Q6: How does the pressure in a car tyre change during a long drive on a hot day?
🚗 Tire Pressure Dynamics
Tire pressure increases due to air temperature rise from road friction and tire flexing. According to Gay-Lussac's Law (P ∝ T at constant V), higher temperature means higher pressure.
This demonstrates real-world application of gas laws and importance of checking tire pressure regularly for safety.
Q7. How does understanding thermal expansion help prevent cracks in sidewalks during hot weather?
🏗️ Expansion Joints
Thermal expansion knowledge leads to installation of expansion joints in sidewalks. These gaps allow concrete to expand in heat without cracking, accommodating dimensional changes from temperature variations.
Proper planning prevents structural damage and extends sidewalk lifespan.
Q8. Imagine you are stuck in the snow with your car. Which would be more effective for melting the snow trapped underneath, a pot of hot water or a high-powered heat lamp?
❄️ Snow Melting Efficiency
Heat Lamp: More effective due to concentrated infrared radiation penetrating snowpack and larger coverage area.
Hot Water: Less efficient because limited surface contact and rapid cooling in cold conditions reduce effectiveness.
Q9. How does the evaporation of water from a plant's leaves help to transport water and nutrients throughout the plant?
🌿 Transpiration Process
Leaf evaporation creates negative pressure (transpiration pull) that draws water upward from roots through xylem vessels. This continuous flow transports dissolved nutrients throughout plant.
Cohesion and adhesion of water molecules maintain column continuity during this process.
Q10. Why does adding ice to a drink cool it down more effectively than adding cold water?
🧊 Latent Heat Advantage
Ice absorbs additional latent heat of fusion during melting (336 J/g for water), providing extra cooling beyond simple temperature difference. Cold water only cools through specific heat capacity.
This makes ice much more effective for rapid drink cooling.
Q11. What are the challenges associated with maintaining the extremely low temperatures required for superconductivity to occur?
❄️ Superconductivity Challenges
Maintaining near-absolute zero temperatures requires complex cryogenic systems using liquid helium or nitrogen. These systems are energy-intensive, expensive to operate, and technically challenging to maintain.
High costs and technical complexity limit widespread practical applications of superconductivity.
Long Answer Questions
Q1. Define latent heat. Differentiate between latent heat and specific latent heat of fusion. Write their formulae.
🔥 Latent Heat Concepts
Latent Heat: Energy absorbed/released during phase change at constant temperature. Used to break/form intermolecular bonds.
Specific Latent Heat of Fusion: Energy required to melt 1kg of substance at melting point without temperature change.
Specific Latent Heat of Fusion: L_f = Q/m
Latent heat depends on mass, while specific latent heat is intensive property independent of mass.
Q2. Differentiate between latent heat of vaporisation and specific latent heat of vaporisation. Give their formulae and units.
| Latent Heat of Vaporization | Specific Latent Heat of Vaporization |
|---|---|
| Total energy for vaporization | Energy per unit mass for vaporization |
| Depends on mass (extensive) | Independent of mass (intensive) |
| Units: Joules (J) | Units: J/kg |
| Q = mL_v | L_v = Q/m |
Q3. What is evaporation? Differentiate between boiling and evaporation. One what factors evaporation depends?
| Evaporation | Boiling |
|---|---|
| Surface phenomenon | Bulk phenomenon |
| Occurs at all temperatures | Occurs at boiling point only |
| Slow process | Rapid process |
| Cooling effect | Heating effect |
🌬️ Evaporation Factors
Temperature: Higher temperature increases evaporation rate
Surface Area: Larger area allows more molecules to escape
Humidity: Lower humidity increases evaporation
Wind Speed: Higher speed removes saturated air faster
Q4. What are linear and volume thermal expansion of solids? Discuss qualitatively the factors upon which these thermal expansions depend.
📏 Thermal Expansion Types
Linear Expansion: Increase in length when heated
Volume Expansion: Increase in all three dimensions when heated
ΔV = βV₀ΔT (Volume)
Where β ≈ 3α for isotropic solids
🌡️ Temperature Change
Greater temperature increase causes more expansion
📐 Original Dimensions
Larger objects expand more for same temperature change
⚗️ Material Type
Different materials have different expansion coefficients
Q5. What are uses of thermal expansion in our daily life? Give examples.
🌡️ Thermometers
Mercury expansion indicates temperature in glass thermometers
🏗️ Expansion Joints
Bridges and roads have gaps for thermal expansion/contraction
🔧 Tight Fitting
Heating metal parts for easier assembly (shrink fitting)
⚡ Bimetallic Strips
Different expansion rates used in thermostats and thermometers
🔩 Jar Opening
Hot water on metal lid expands it for easier opening
⚖️ Pendulum Clocks
Compensation for pendulum length changes with temperature
Q6. Explain thermal expansion of liquids in detail.
💧 Liquid Expansion Types
Real Expansion: Actual liquid volume increase including container expansion
Apparent Expansion: Observed expansion excluding container effect
Real expansion is always greater than apparent expansion due to container expansion.
Q7. Discuss the application of bimetallic strips in temperature control devices like thermostats. Explain the principle of thermal expansion that allows the bimetallic strip to function, and illustrate how the differing expansion rates of the two metals are utilized in practical.
⚙️ Bimetallic Strip Principle
Two different metals bonded together expand at different rates when heated. The strip bends toward the metal with lower expansion coefficient.
This bending movement operates electrical switches in thermostats for temperature control.
🏠 Home Thermostats
Control heating/cooling systems based on room temperature
🚗 Automotive
Engine temperature regulation and indicator systems
❄️ Refrigerators
Compressor cycling based on internal temperature
🔥 Fire Alarms
Heat detection for emergency response systems
Q8. What is superconductivity? Explain the phenomenon in detail. What is their scope in future world?
⚡ Superconductivity Fundamentals
Definition: Zero electrical resistance and magnetic field expulsion below critical temperature
Meissner Effect: Complete diamagnetism - expulsion of magnetic fields
BCS Theory: Electron pairs (Cooper pairs) move without resistance through crystal lattice
🔌 Power Transmission
Lossless electricity transfer over long distances
🚄 Maglev Trains
Frictionless magnetic levitation transportation
🏥 Medical Imaging
High-field MRI machines for detailed diagnostics
💻 Quantum Computing
Superconducting qubits for advanced computation
📚 Master 10th Physics Thermal Transformation
This comprehensive guide covers all essential concepts from Chapter 11 Thermal Transformation. Understanding heat transfer, phase changes, and thermal properties is crucial for both academic success and appreciating everyday thermal phenomena.
Key Topics Covered: Specific heat capacity, latent heat, thermal expansion, evaporation, boiling, phase changes, and practical applications.
© House of Physics | 10th Physics Federal Board Notes: Chapter 11 Thermal Transformation
Complete solved exercises based on Federal Board curriculum with detailed explanations and practical applications
For more educational resources contact: aliphy2008@gmail.com
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