Heat and Thermodynamics part-(1)

Total Questions: 45

1. In an ecosystem, flow of energy declines as it passes from lower to higher trophic level. This is explained by the following: [M.P.P.C.S. (Pre) 2023]

(a)First law of thermodynamics
(b)Second law of thermodynamics
(c)Newton's second law
(d)Newton's third law

Correct Answer: (b)Second law of thermodynamics

Solution:In an ecosystem, flow of energy declines as it passes from lower to higher trophic level. This is explained by the second law of thermodynamics. The second law of thermodynamics states that as energy is transferred or transformed, more and more of it is wasted. That means, every activity and energy transformation is accompanied by dissipation of energy.

The energy decreases from one trophic level to the next trophic level because energy is lost as metabolic heat during transfer of energy. When food energy passes from producers to herbivores to carnivores, only 10% of energy is transferred from one trophic level to another trophic level.

2. The temperature point at which solid, liquid and gaseous states may stay together is known as: [67th B.P.S.C. (Pre) 2022]

(a) boiling point
(b) melting point
(c) freezing point
(d) triple point
(e) None of the above/More than one of the above

Correct Answer: (d) triple point

Solution:The temperature point at which solid, liquid and gaseous states may stay together is known as triple point. In thermodynamics, a substance's triple point is the unique combination of temperature and pressure at which the solid phase, liquid phase, and gaseous phase can all coexist in thermodynamic equilibrium.

By international agreement, the triple point of water has been assigned a value of 273.16 K (0.01°C, 32.018 °F) at partial vapour pressure of 611.657 pascals (6.11657 m bar; 0.0060366 atm). The triple point of water was earlier used to define the Kelvin, the base unit of thermodynamic temperature in the SI system.

3. Transfer of heat by convection can take place in [M.P.P.C.S.(PRE) 2017]

(a) solids and liquids
(b) solids and vacuum
(c) gases and liquids
(d) vacuum and gases

Correct Answer: (c) gases and liquids

Solution:Convection is a mode of heat transfer by actual motion of matter it is possible only in fluids and gases. convection can be natural and forced.

4. A liquid remains hot or cold for a long time in thermos flask because there is no loss or gain of heat by [U.P.P.C.S.(pre) 2019]

(a) conduction
(b) convection and radiation
(c) both (a) and (b)
(d) none of the above

Correct Answer: (c) both (a) and (b)

Solution:Thermos flask have a vacuum gap between the inner chamber and the outer wall so there is no loss or gain of heat by conduction, convection and radiation thus a liquid remains hot or cold for a long time in thermos flask.

5. Steam at 100°C causes more server burns than the water at the same temperature because: [Chhattisgarh P.C.S.(PRE) 2008]

(a) steam is a gas
(b) steams provide more heat
(c)steam is highly combustible
(d)steam exerts more pressure

Correct Answer: (b) steams provide more heat

Solution:Steam at 100°C causes more severe burns than the water at the same temperature because steam provides more heat. The boiling point of water is 100 degree celsius. At this temperature, the water will begin to change from the liquid state to the gaseous state.

For this change to take place, additional energy is required. In fact, every gram of liquid water requires 540 calories of heat energy to convert it to steam. This is called the latent heat of vaporization or latent heat of steam.

So while they both would exist at the same temperature the steam would have a lot more heat energy due to the addition of 540 calories per gram of heat energy that has been absorbed .This is why steam burns are worse than that water burns.

6. The hand burns more by steam comparatively to the boiling water because - [U.P.P.C.S.(PRE) 1993]

(a) the steam has a latent heat
(b) steam sneaked into the body
(c) the steam has more power
(d) steam is gig

Correct Answer: (a) the steam has a latent heat

Solution:Steam at 100°C causes more severe burns than the water at the same temperature because steam provides more heat. The boiling point of water is 100 degree celsius.

At this temperature, the water will begin to change from the liquid state to the gaseous state. For this change to take place, additional energy is required. In fact, every gram of liquid water requires 540 calories of heat energy to convert it to steam.

This is called the latent heat of vaporization or latent heat of steam.so while they both would exist at the same temperature the steam would have a lot more heat energy due to the addition of 540 calories per gram of heat energy that has been absorbed .This is why steam burns are worse than that water burns.

7. The heat required in calorie to convert one gram of ice at 0°C to steam at 100°C at approximately [Uttarakhand Lower Sub.(PRE) 2010]

(a) 80 calorie
(b) 336 calorie
(c) 720 calorie
(d) 620 calorie

Correct Answer: (c) 720 calorie

Solution:Latent heat of Melting = 80 calorie/gram The heat required for ice at 0°C to convert in water = 80 calorie Required heat to enhance the temperature of water from 0°C to 100 °C =100 calorie
Latent heat of vaporization =540 calorie/gram
Hence the energy required to convert water into vapour at 100°C = 540 calorie.
Total heat required = 80+100+540 = 720 calorie.

8. At what temperature are the reading of a centigrade and fahrenheit thermometer the same ? [U.P.P.C.S.(MAINS)2015, U.P.U.D.A./L.D.A.(PRE) 2003, I.A.S. (PRE) 1993]

(a) -40°C
(b) 212°C
(c) 40°C
(d) 100°C

Correct Answer: (a) -40°C

Solution:-40°C is the temperature at which the reading are same in both degree centigrade and in fahrenhiet scale relation between degree centigrade and degree fahrenheit is

C/5=(F-32)/9
Placing F=-40 to verify
C=(-40-32)×5/9=-72×5/9=-40

9. At what degree are the centigrade and fahrenheit temperature the same ? [M.P.P.C.S.(PRE) 1994,1995]

(a) 100°C
(b) 80°C
(c) -32°C
(d) -40°C

Correct Answer: (d) -40°C

Solution:-40°C is the temperature at which the reading are same in both degree centigrade and in fahrenhiet scale relation between degree centigrade and degree fahrenheit is

C/5=(F-32)/9
Placing F=-40 to verify
C=(-40-32)×5/9=-72×5/9=-40

10. At which temperature the celsius and fahrenheit scales coincides ? [67th B.P.S.C.(PRE)(re.exam) 2020]

(a) 0°C
(b) 10°C
(c) -40°C
(d) 40°C
(e) none of the above /more than one of the above

Correct Answer: (c) -40°C

Solution:-40°C is the temperature at which the reading are same in both degree centigrade and in fahrenhiet scale relation between degree centigrade and degree fahrenheit is

C/5=(F-32)/9
Placing F=-40 to verify
C=(-40-32)×5/9=-72×5/9=-40

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Heat and Thermodynamics part-(1)