Food is cooked faster in a pressure cooker because
- A.The higher pressure raises the boiling point of water
- B.The higher pressure lowers the boiling point of water
- C.Steam has a higher specific heat than water
- D.The cooker is a better conductor of heat than an open pan
Correct answer
Explanation
The correct answer is A. A cooker is sealed, so the steam it produces cannot escape and the pressure inside rises. Since the boiling point of a liquid rises with the pressure on it, water in a cooker boils well above a hundred degrees Celsius, and food cooking at that higher temperature is ready sooner.
Option B states the opposite and describes what happens on a mountain, where the pressure is low, water boils below a hundred degrees and cooking takes longer. Option C is wrong as a reason, and the burning power of steam comes from its latent heat rather than from specific heat. Option D is wrong because the material of the vessel affects only how quickly heat reaches the water; it cannot raise the temperature at which the water boils, which is what saves the time.
Read the full article: Heat and Thermodynamics: Laws, Latent Heat and Transfer
Practice Questions
View allThe SI unit of heat is the
- A.Calorie
- B.Joule
- C.Kelvin
- D.Watt
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Heat is a form of energy in transit, so it is measured in the same unit as work and energy, the joule, which is one newton metre.
Read the full explanation →Water has its maximum density at a temperature of
- A.0 degrees Celsius
- B.4 degrees Celsius
- C.100 degrees Celsius
- D.Minus 4 degrees Celsius
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Water behaves abnormally between zero and four degrees: it contracts as it is heated in that range and expands again above four degrees, so the same mass occupies its least volume, and therefore has its greatest density, at four degrees Celsius.
Read the full explanation →The latent heat of vaporisation of water is about
- A.80 calories per gram
- B.540 calories per gram
- C.336 calories per gram
- D.2260 calories per gram
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This is the heat that one gram of water at a hundred degrees Celsius must absorb to become steam at the same temperature, with no rise in temperature at all; the same quantity is released when steam condenses back to water.
Read the full explanation →In a vacuum flask, the vacuum between the two walls prevents heat transfer mainly by
- A.Conduction and convection
- B.Radiation only
- C.Conduction only
- D.Neither conduction nor convection
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Both of these modes need matter: conduction passes energy from particle to particle and convection carries it by the movement of a fluid.
Read the full explanation →The first law of thermodynamics is essentially a statement of
- A.The conservation of energy
- B.The increase of entropy
- C.Thermal equilibrium
- D.The unattainability of absolute zero
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The first law says that the heat supplied to a system is equal to the increase in its internal energy plus the external work it does.
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