Temperature — Set 2

Correct Answer: B. 35°C to 42°C

• **35°C to 42°C** = Clinical thermometers cover a narrow range around normal human body temperature (37°C) to detect fever or hypothermia accurately. • **37°C** — Normal human body temperature is about 37°C; the restricted range (35–42°C) improves sensitivity and scale readability. • 💡 Wrong-option analysis: −50°C to 50°C: too wide a range for a clinical thermometer; 100°C to 200°C: far above any safe body temperature; 0°C to 100°C: a laboratory range, not designed for clinical use.

Correct Answer: B. Seebeck effect

• **Seebeck effect** = When two dissimilar metal wires are joined at two junctions held at different temperatures, an electromotive force (emf) is generated — this is the Seebeck effect. • **Thomas Johann Seebeck (1821)** — The magnitude of the emf depends on the temperature difference between the hot and cold junctions. • 💡 Wrong-option analysis: Hall effect: voltage generated by a current in a magnetic field, unrelated to temperature; Photoelectric effect: emission of electrons by light; Doppler effect: change in frequency due to relative motion.

Correct Answer: C. Electrical resistance of platinum

• **Electrical resistance of platinum** = Platinum's resistance increases nearly linearly with temperature, allowing precise temperature measurement over a wide range. • **R = R₀(1 + αT)** — The resistance varies with temperature according to this linear approximation, where α is the temperature coefficient of resistance. • 💡 Wrong-option analysis: Mass of platinum: mass does not change with temperature (significantly); Magnetic field around platinum: not a useful thermometric property; Length of platinum wire: length does change but resistance is the measured quantity.

Correct Answer: B. -40°

• **−40°** = Setting C = F in the equation F = (9/5)C + 32 gives C = −40°, so −40°C = −40°F — the unique crossover point of the two scales. • **F = (9/5)C + 32 → C(1 − 9/5) = 32 → C = −40** — Solving algebraically yields −40° as the only temperature where both scales agree. • 💡 Wrong-option analysis: 100°: on Celsius it is the boiling point; on Fahrenheit it is 37.8°C; 0°: 0°C = 32°F, they are not equal; 40°: 40°C = 104°F, not equal.

Correct Answer: C. 273.16 K

• **273.16 K** = The triple point of water is defined as exactly 273.16 K — the unique temperature and pressure where solid, liquid, and vapor coexist in equilibrium. • **0.01°C** — The triple point corresponds to 0.01°C (slightly above the ice point of 0°C), at a pressure of 611.73 Pa. • 💡 Wrong-option analysis: 273.15 K: that is the ice point (0°C), not the triple point; 373.15 K: that is the boiling point of water (100°C); 212 K: corresponds to about −61°C, far from the water triple point.

Correct Answer: C. Temperature is an intensive property

• **Temperature is an intensive property** = Temperature does not depend on the amount of substance — a cup and a tank of water at 25°C have the same temperature regardless of their size. • **Intensive vs. extensive** — Intensive properties (temperature, pressure, density) are independent of amount; extensive ones (mass, volume, heat energy) scale with amount. • 💡 Wrong-option analysis: Temperature is measured in joules: joule is the unit of energy, not temperature; Temperature is always proportional to mass: temperature is independent of mass; Temperature depends on the amount of substance present: this describes an extensive property, which temperature is not.

Correct Answer: C. 273.15 K

• **273.15 K** = Convert 0°C to kelvin by adding 273.15; so the ice point equals 273.15 K. • **0°C ↔ 273.15 K** — This is the fundamental link between the Celsius and kelvin scales, used in gas law calculations. • 💡 Wrong-option analysis: 0 K: that is absolute zero (−273.15°C); 373.15 K: that is the boiling point of water (100°C); 100 K: corresponds to −173.15°C.

Correct Answer: A. 27°C

• **27°C** = Convert kelvin to Celsius by subtracting 273.15; so 300 − 273.15 ≈ 27°C. • **300 K ≈ 27°C** — Room temperature is often approximated as 300 K (27°C) in physics calculations for simplicity. • 💡 Wrong-option analysis: 300°C: that would be 573 K, not 300 K; 73°C: that would be 346 K; −27°C: that would be 246 K.

Correct Answer: C. Thermal electromagnetic radiation

• **Thermal electromagnetic radiation** = A pyrometer measures temperature without contact by detecting the thermal radiation (infrared and/or visible light) emitted by a hot object. • **Stefan-Boltzmann law: P ∝ T⁴** — The intensity of thermal radiation increases strongly with temperature, enabling remote temperature measurement. • 💡 Wrong-option analysis: X-rays only: X-rays are not emitted by ordinary hot objects at measureable levels; Sound waves: sound is mechanical, not electromagnetic radiation; Radio waves only: hot objects emit mainly infrared, not radio waves.

Correct Answer: D. Resistance decreases significantly

• **Resistance decreases significantly** = Most thermistors are Negative Temperature Coefficient (NTC) devices — their resistance drops sharply as temperature rises, making them very sensitive sensors. • **NTC vs PTC** — NTC thermistors have decreasing resistance with temperature; Positive Temperature Coefficient (PTC) ones increase — NTC is more common in sensing. • 💡 Wrong-option analysis: Resistance increases linearly always: this describes metal conductors like platinum, not typical NTC thermistors; Resistance becomes infinite: that would make the thermistor useless; Resistance becomes exactly zero: that would describe a superconductor at critical temperature.