⚡ Fast Revision: Heat and Temperature
- Heat: A form of energy that flows from a body at a higher temperature to a body at a lower temperature.
- Temperature: The degree of hotness or coldness of a body.
- Thermal Equilibrium: When two bodies in contact reach the same temperature, heat flow stops.
Heat SI Unit: Joule (J) | Common Unit: calorie (cal)
Temperature SI Unit: Kelvin (K) | Common Unit: Celsius (°C)
| Quantity | Measurement Instrument |
|---|---|
| Temperature | Thermometer |
| Heat Energy | Calorimeter |
Thinking heat and temperature are the same. Fix: Two bodies can have the same temperature but contain different amounts of heat (based on mass and material).
⚡ Fast Revision: Temperature Scales & Conversion
- Celsius Scale: LFP (Ice point) is 0°C; UFP (Steam point) is 100°C.
- Fahrenheit Scale: LFP is 32°F; UFP is 212°F.
- Kelvin Scale: SI Unit. Absolute Zero is 0 K ($-273.15°C$). No negative values.
$\frac{C}{5} = \frac{F - 32}{9}$
$K = C + 273$
| Scale | LFP (Ice Point) | UFP (Steam Point) |
|---|---|---|
| Celsius (°C) | 0°C | 100°C |
| Fahrenheit (°F) | 32°F | 212°F |
| Kelvin (K) | 273 K | 373 K |
Using the "degree" symbol (°) with Kelvin. Fix: Kelvin is an absolute scale; always write K (e.g., 300 K), never 300°K.
⚡ Fast Revision: Transfer of Heat
- Conduction: Transfer in solids through particle vibration without actual movement of particles.
- Convection: Transfer in fluids (liquids/gases) where particles actually move in currents.
- Radiation: Transfer through vacuum or air via electromagnetic waves; no medium required.
| Mode | Medium Required? | Speed |
|---|---|---|
| Conduction | Yes (Solids) | Slow |
| Convection | Yes (Fluids) | Medium |
| Radiation | No (Vacuum) | Fastest (Speed of Light) |
Convection: Sea breeze (day) and Land breeze (night).
Radiation: Heat from the Sun reaching the Earth.
Thinking air is a good conductor. Fix: Air is an insulator; heat travels through it primarily by convection or radiation.
⚡ Fast Revision: Thermal Expansion in Solids, Liquids & Gases
- Definition: The increase in size (length, area, or volume) of a substance on heating.
- Order of Expansion: Gases expand the most, followed by liquids, and solids expand the least for the same rise in temperature.
- Reason: Heating increases kinetic energy, causing particles to move further apart.
| State of Matter | Type of Expansion |
|---|---|
| Solids | Linear (length), Superficial (area), and Cubical (volume). |
| Liquids | Only Cubical (volume) expansion. |
| Gases | Highly significant cubical expansion. |
Water behaves uniquely between 0°C and 4°C. It contracts on heating and expands on cooling in this range.
Density: Water is densest at exactly 4°C.
Thinking railway tracks are laid without gaps. Fix: Small gaps are left between rails to allow for expansion in summer, preventing the tracks from buckling.
⚡ Fast Revision: Thermos Flask & Summary
- Vacuum: Between double glass walls prevents heat loss by Conduction and Convection.
- Silvered Walls: Reflect heat back, preventing loss by Radiation.
- Insulated Stopper: Made of cork or plastic to minimize heat loss from the top.
| Flask Feature | Prevents Heat Loss By... |
|---|---|
| Vacuum between walls | Conduction & Convection |
| Shiny silver coating | Radiation |
| Plastic/Cork lid | Conduction |
Absolute Zero: -273.15°C or 0 K (Molecular motion stops).
Bimetallic Strip: Used in thermostats; works on unequal expansion of two metals.
Assuming a thermos flask keeps liquids hot forever. Fix: Heat is eventually lost through the stopper and the glass neck, which cannot be perfectly insulated.