TEMPERATURE: Measure of thermal energy
- Celsius: Water freezes at 0°C, boils at 100°C
- Kelvin: Absolute scale, 0K = -273°C (absolute zero)
- Fahrenheit: Used in some countries
Conversion: K = °C + 273.15

HEAT: Transfer of thermal energy between objects
- Not same as temperature!
- Temperature = measure of molecular motion
- Heat = transfer of energy due to temperature difference

THERMAL ENERGY: Total kinetic energy of particles
- Depends on both temperature and amount of substance

FIRST LAW (Energy Conservation):
Q = ΔU + W

Where:
Q = Heat added to system
ΔU = Change in internal energy
W = Work done by system

Meaning: Energy cannot be created or destroyed;
it changes form or transfers between objects

Example: When heating water:
- Heat energy (Q) makes water molecules move faster
- Some energy increases temperature (ΔU)
- Some energy does work expanding the liquid (W)

SECOND LAW (Entropy):
In any spontaneous process:
Entropy (disorder) of isolated system increases

Meaning:
- Heat flows from hot object to cold object
- Never spontaneously flows the other way
- Efficiency of heat engines is never 100%
- Everything tends toward disorder

Example:
- Hot tea cools down (entropy increases)
- Cold tea never spontaneously heats (violates 2nd law)

Heat Capacity (C):
Energy needed to raise temperature of substance by 1°C
C = Q / ΔT
Units: J/°C or cal/°C

Specific Heat (c):
Heat capacity per unit mass
c = Q / (m × ΔT)
Units: J/(kg·°C) or cal/(g·°C)

Water specific heat: 4186 J/(kg·°C)
- Highest of common materials
- Why water heats/cools slowly
- Why oceans regulate climate

Calculation Example:
How much heat to raise 2 kg water by 10°C?
Q = m × c × ΔT
  = 2 kg × 4186 J/(kg·°C) × 10°C
  = 83,720 J

1. CONDUCTION
   Through solid material (no particle movement)
   Example: Metal spoon gets hot in hot tea
   
   Rate of heat transfer:
   Q = (k × A × ΔT × t) / d
   
   Where:
   k = Thermal conductivity
   A = Cross-sectional area
   ΔT = Temperature difference
   t = Time
   d = Thickness
   
   Good conductors: Copper, Aluminum, Silver
   Poor conductors: Wood, Foam, Rubber

2. CONVECTION
   Through fluid movement (liquid or gas)
   Example: Heat rising from radiator in room
   
   Process:
   - Hot fluid becomes less dense
   - Rises up
   - Cool fluid sinks down
   - Creates circulation (convection current)
   
   Used in: Ovens, cooling systems, weather patterns

3. RADIATION
   Through electromagnetic waves (no medium needed)
   Example: Sun heating Earth (through vacuum of space)
   
   Stefan-Boltzmann Law:
   P = σ × A × T⁴
   
   Where:
   P = Power radiated
   σ = Stefan-Boltzmann constant
   A = Surface area
   T = Absolute temperature (Kelvin)
   
   Key insight: Power depends on T⁴
   - Small temperature increase = huge increase in radiation
   - Why hot objects cool quickly at first

ISOTHERMAL (Constant Temperature)
- ΔT = 0 (no temperature change)
- Example: Melting ice at 0°C
- For ideal gas: PV = constant
- First law: Q = W (all heat becomes work)

ADIABATIC (No Heat Transfer)
- Q = 0 (no heat exchange with surroundings)
- Example: Rapid compression of gas
- First law: ΔU = -W (temperature changes)
- Used in: Diesel engines, expanding clouds

ISOCHORIC (Constant Volume)
- V = constant (no volume change)
- W = 0 (no work done)
- First law: Q = ΔU (heat changes temperature)
- Example: Heating gas in rigid container

ISOBARIC (Constant Pressure)
- P = constant
- Example: Heating gas in piston (allows expansion)
- First law: Q = ΔU + W
- Most common in nature

Main Ideas:
1. Gas consists of particles in random motion
2. Collisions are perfectly elastic
3. Volume of particles << volume of gas
4. Temperature proportional to average kinetic energy

Ideal Gas Law:
PV = nRT

Where:
P = Pressure (Pa)
V = Volume (m³)
n = Number of moles
R = Gas constant = 8.314 J/(mol·K)
T = Absolute temperature (K)

Example:
A balloon at 1 atm, 20°C contains 22.4L air (1 mole)
Find if heated to 40°C at constant pressure:

V₁/T₁ = V₂/T₂ (Charles's Law)
V₂ = V₁ × (T₂/T₁)
   = 22.4 × (313K / 293K)
   = 23.9 L

The balloon expands by 1.5 L!

SOLID ↔ LIQUID (Melting/Freezing)
- Latent heat of fusion: Energy to change state
- Ice at 0°C needs 334,000 J/kg to become water
- Temperature remains constant during phase change

LIQUID ↔ GAS (Vaporization/Condensation)
- Latent heat of vaporization: Much larger
- Water at 100°C needs 2,260,000 J/kg to become steam
- This is why steam causes severe burns

Temperature vs Heat Graph:

### Problem-Solving Examples

**Example 1: Heat Transfer Problem**

**Example 2: Phase Change Problem**

### Real-World Applications

**Heat Engines (Convert Heat to Work):**

**Heat Pumps (Move Heat Against Gradient):**

### Download Physics Notes by Units

**Applied Physics Homework & Notes:**
- [Download PDF of unit-1](https://drive.google.com/uc?export=download&id=1Q6Mafb-Q2KQq6x_Fd_PtO7Xk8OiGQTWg)
- [Download PDF of unit-2 and assignment-1](https://drive.google.com/uc?export=download&id=1WO9unQcZ3ZwWe3TjIpjn-gjUlDzKj_5u)
- [Download PDF of Unit-3 and assignment-2](https://drive.google.com/uc?export=download&id=12vKGUCECTBcrGln8Zh-LvU1xfCGtNygd)
- [Download PDF of Unit-4&5 and assignment-4&5](https://drive.google.com/uc?export=download&id=1C2M71mp-__Vcrsx5FVUs-_s9XJTPMTHh)

Each PDF contains:
- Complete unit theory
- Worked examples
- Practice problems
- Assignments with solutions

### Key Formulas Summary

### Study Tips for Success

1. **Understand concepts first**: Don't just memorize formulas
2. **Work through examples**: See how concepts apply
3. **Practice problems**: Start easy, progress to hard
4. **Use diagrams**: Draw phase diagrams, pressure-temperature graphs
5. **Connect to real life**: Think about applications
6. **Group study**: Discuss concepts with classmates
7. **Ask questions**: Clarify doubts immediately
8. **Revise regularly**: Re-read notes weekly

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**Applied Physics is challenging but fascinating. Master thermodynamics and you'll understand everything from engines to weather to refrigerators!**