Temperature & Heat – Quick Notes 🚀
1. Heat vs Temperature 🔥
Heat is the energy that flows from a hotter body to a colder one whenever there’s a temperature difference — it’s measured in joules (J), while temperature itself is measured in kelvin (K) or the familiar degree Celsius (°C) :contentReference[oaicite:0]{index=0}.
2. Measuring Temperature 🌡️
- Thermometers exploit a property that changes with temperature (for example, how much a liquid expands).
- To give numbers to temperatures, we pick two handy reference points: the ice point and the steam point of pure water.
- Those points sit at 0 °C & 100 °C on the Celsius scale and at 32 °F & 212 °F on the Fahrenheit scale. The Fahrenheit scale squeezes in 180 equal parts between its fixed points, whereas Celsius has 100 :contentReference[oaicite:1]{index=1}.
The two scales talk to each other through
\[ \frac{t_F – 32}{180} = \frac{t_C}{100} \tag{10.1} \] :contentReference[oaicite:2]{index=2}
3. Ideal Gas & Absolute Temperature 🌬️
- Boyle’s law: \( PV = \text{constant} \) when \( T \) is steady :contentReference[oaicite:3]{index=3}.
- Charles’ law: \( \dfrac{V}{T} = \text{constant} \) when \( P \) is steady :contentReference[oaicite:4]{index=4}.
- Put them together and every low-density gas obeys the ideal-gas equation
\( PV = \mu R T \tag{10.2}\) where \( R = 8.31\;\text{J mol}^{-1}\text{K}^{-1} \) :contentReference[oaicite:5]{index=5}. - Plotting pressure vs temperature at constant volume gives a straight line that kisses zero pressure at –273.15 °C. That chill limit is absolute zero.
- This leads to the Kelvin scale, defined by
\( T = t_C + 273.15 \tag{10.3}\) :contentReference[oaicite:6]{index=6}.
4. Thermal Expansion 🌡️➕📏
- Most substances swell when warmed. Everyday trick: run a tight metal lid under hot water — the lid expands and loosens. Likewise, mercury rises in a thermometer when the bulb warms up :contentReference[oaicite:7]{index=7}.
High-Yield NEET Nuggets ✨
- Fahrenheit ↔ Celsius conversion: \(\dfrac{t_F – 32}{180} = \dfrac{t_C}{100}\).
- The ideal-gas equation \( PV = \mu R T \) and the value of \( R \).
- Absolute zero (–273.15 °C) and the Kelvin relation \( T = t_C + 273.15 \).
- Special cases: Boyle’s law (constant T) and Charles’ law (constant P).
- Conceptual questions on everyday thermal-expansion examples.
You’ve got this! Keep practicing, and these ideas will feel like second nature 🤓👍.
