Tag: physics

Questions Related to physics

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

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

  1. True

  2. False

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Correct Option: B
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.

Why mercury do not evaporate at room temperature?

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

  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

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Correct Option: B
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.

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

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

  1. True

  2. False

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Correct Option: A
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.

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

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

  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.

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Correct Option: C
Explanation:

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

Relative humidity is the percentage of the

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

  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

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Correct Option: C
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.

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

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

  1. exceeds the atmospheric pressure

  2. becomes less than the atmospheric pressure

  3. becomes equal to the atmospheric pressure

  4. becomes zero

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Correct Option: C
Explanation:

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

Water in an earthen pitcher gets cooled due to

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

  1. slower rate of evaporation

  2. faster rate of evaporation

  3. no evaporation at all

  4. some unknown reason

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Correct Option: B
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.

Drying up of clothes is fastest on a 

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

  1. hot day without winds

  2. cold day without winds

  3. hot,dry and windy day

  4. humid and windy day

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Correct Option: C
Explanation:

Evaporation is the key process involved in the drying up of clothes. Since evaporation is fastest in dry weather on a windy day, clothes dry faster on these days.

Dogs hang out their tongue during summers to achieve cooling. Which phenomenon is involved in the process?

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

  1. Condensation

  2. Evaporation

  3. Vaporization

  4. Fusion

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Correct Option: B
Explanation:

Dogs hang out their tongue during summers. This helps produce a cooling effect due to evaporation.

Salt is extracted from sea-water by

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

  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.

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Correct Option: D
Explanation:

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