Physics - Heat & Thermo Question with Solution | TestHub
PhysicsHeat & ThermoThermal ExpansionMedium2 minQB
PhysicsMediumstatement
Water at 80°C in a flask boils vigorously when the air above it is pumped out, with no heating. This is because:
Statement I: The boiling point of water rises at low pressure.
Statement II: Its saturated vapour pressure at C exceeds the reduced external pressure; the latent heat is taken from the water itself, which cools.
Options:
Answer:
C
Solution:
Boiling starts when vapour pressure equals the external pressure. Lowering the pressure below about 47 kPa (vapour pressure at 80°C) makes the water boil, drawing latent heat from itself so it cools. Statement I is false and Statement II true. Correct option: (C).
Subject:PhysicsTopic:Heat & ThermoSubtopic:Thermal Expansion
⏱ 2mℹ️ Source: QB
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