Measurement of Temperature 🚀
1. Heat and Temperature — spot the difference! 🔥🌡️
Heat is energy that moves from a hotter body to a colder one whenever there is a temperature gap — that’s why an ice cube chills your drink and a cup of tea warms your hands. The energy is measured in joules (J), while temperature itself is expressed in kelvin (K) or, more commonly in daily life, degrees Celsius (°C) :contentReference[oaicite:0]{index=0}.
2. Thermometers: turning change into numbers 📏
2.1 Thermometric property
Any physical property that changes noticeably with temperature can be pressed into service. The classic choice is the volume of a liquid. Mercury and coloured alcohol expand almost perfectly linearly over a wide span, making them ideal for liquid-in-glass thermometers :contentReference[oaicite:1]{index=1}.
2.2 Calibration – locking down the scale 🔒
- Two fixed reference points anchor every temperature scale.
- The most convenient are the ice point (melting of pure ice) and the steam point (boiling of pure water) at standard pressure :contentReference[oaicite:2]{index=2}.
- Because every substance expands differently, we rely on these reproducible physical events rather than an “absolute” expansion benchmark.
3. Everyday temperature scales 🧭
3.1 Celsius vs Fahrenheit
- Ice point: 0 °C | 32 °F
- Steam point: 100 °C | 212 °F
- Number of equal divisions between the two: 100 on the Celsius scale, 180 on the Fahrenheit scale :contentReference[oaicite:3]{index=3}.
Conversion made easy: \( \displaystyle \frac{t_F – 32}{180} = \frac{t_C}{100} \) 😎 :contentReference[oaicite:4]{index=4}
3.2 The absolute (kelvin) scale
Physicists love kelvin because it starts at absolute zero. A handy link between the two common units is \( \displaystyle T(\text{K}) = t({}^{\circ}\text{C}) + 273.15 \) :contentReference[oaicite:5]{index=5}.
4. Gas thermometers & the road to the ideal-gas laws 💨
Gas thermometers sidestep the “different liquids, different readings” problem: all dilute gases expand in almost the same way. To describe a given sample of gas we track its pressure (P), volume (V) and absolute temperature (T) :contentReference[oaicite:6]{index=6}.
Boyle’s law 📉 At constant temperature, \( PV = \text{constant} \) :contentReference[oaicite:7]{index=7}.
Charles’ law 📈 At constant pressure, \( \displaystyle \frac{V}{T} = \text{constant} \) :contentReference[oaicite:8]{index=8}.
With pressure, volume and temperature all changing, these two ideas fuse into a single relationship (developed further in later sections) :contentReference[oaicite:9]{index=9}.
5. High-Yield NEET Nuggets ⚡
- Fahrenheit–Celsius conversion: \( \displaystyle \frac{t_F – 32}{180} = \frac{t_C}{100} \). Show up often in “quick-convert” questions.
- Fixed points of water: 0 °C/100 °C are the bedrock of most practical thermometers.
- Boyle’s and Charles’ laws: the twin pillars for gas-law problems.
- Kelvin link: \( T = t + 273.15 \) — every gas-law equation uses kelvin, not °C.
- Thermometric properties: why mercury/alcohol’s linear expansion is so handy for lab apparatus.
You’ve got this! Keep practising conversions and the basic gas laws, and those NEET questions will feel like a breeze 💪✨
