Tag: physics

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Multiple choice physics the kinetic model of matter evaporation heat, internal energy and work phase change

When the temperature of water rises, the rate of evaporation decreases. State whether true or false.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
The statement if False.
Actually, rate of evaporation of a liquid decreases as the temperature decreases. As intermolecular force increase rate of evaporation decreases. This happens because intermolecular force make it less likely for the molecules on the surface to escape from liquid and become vapour gas. As temperature increases rate of evaporation increases.
Multiple choice physics the kinetic model of matter evaporation heat, internal energy and work phase change

Why mercury do not evaporate at room temperature?

  1. Because melting point of mercury is higher

  2. Because boiling point of mercury is higher

  3. Because boiling point of mercury is lower

  4. Because boiling point of mercury is equal to room temperature
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Evaporation is a process in which some molecules of a liquid, which have greater kinetic energy, escape from the liquid and enter the atmosphere.

When the temperature of the liquid is closer to its boiling point, greater is the evaporation. 
Besides the boiling point being higher, the cohesive force of attraction among the molecules of mercury is greater than other liquids like water. This further reduces the evaporation rate.

Multiple choice physics the kinetic model of matter evaporation heat, internal energy and work phase change

Evaporation is the process of changing liquid into vapour below its boiling point. State whether true or false.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Evaporation is the process of changing liquid into vapour below B.P. (boiling point)
It is the type of vaporisation that occurs on the surface of liquid due to increase in temperature or pressure it changes liquid into gaseous phase before reaching to B.P. The surrounding gas must not be saturated by evaporating substance.
Multiple choice physics the kinetic model of matter evaporation heat, internal energy and work phase change

A dog pants with its tongue sticking out on a hot day. Which of the following is the correct reason?

  1. It is its habit

  2. Producing more saliva cools down the body temperature.

  3. Saliva vapourises, cooling the tongue

  4. It is a genetic disease found in few animals like dogs.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Evaporation causes cooling.
A dog pants with its tongue sticking out on a hot day because its saliva vapourises, cooling the tongue.

Multiple choice physics the kinetic model of matter evaporation heat, internal energy and work phase change

Relative humidity is the percentage of the

  1. absolute humidity value to the amount of humidity actually present

  2. increase of humidity/absolute humidity

  3. amount of humidity actually present to the absolute humidity

  4. none of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The ratio of actual amount of water vapour present in volume of air at a given temperature to maximum amount that air could hold at that temperature, expressed as percentage is relative humidity.

Multiple choice physics the kinetic model of matter evaporation heat, internal energy and work phase change

The molecules of liquid change into vapour when the pressure of molecules of liquid

  1. exceeds the atmospheric pressure

  2. becomes less than the atmospheric pressure

  3. becomes equal to the atmospheric pressure

  4. becomes zero
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

When the pressure of molecules of liquid become equal to the atmospheric pressure, the molecules of liquid change into vapours.

Multiple choice physics the kinetic model of matter evaporation heat, internal energy and work phase change

Water in an earthen pitcher gets cooled due to

  1. slower rate of evaporation

  2. faster rate of evaporation

  3. no evaporation at all

  4. some unknown reason
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Earthen pots are used in summer. The pot has several pores through which water rinses out to the outer surface of the earthen pot and evaporates. In this process it takes away heat from the water inside the pitcher. As a result, the water inside gets cooled.

Multiple choice physics the kinetic model of matter evaporation heat, internal energy and work phase change

Salt is extracted from sea-water by

  1. Treating with chemicals depositing salt at the bottom

  2. Filtering the water by nets blocking the salt.

  3. Boiling the water by coil leaving behind the salt.

  4. Evaporating the water by sun leaving behind the salt.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Salt is produced by direct evaporation of sea-water in sun. This process is cheapest and most efficient.