Heat and Thermodynamics part-(2)

Total Questions: 44

1. When ice melts then- [U.P.P.C.S.(pre) 2012]

(a) volume increase.
(b) volume decrease.
(c) mass increase.
(d) mass decrease.

Correct Answer: (b) volume decrease.

Solution:• Ice is less dense than water: Water molecules in ice form a crystalline structure with more space between them compared to liquid water. This makes ice less dense, which is why it floats.

• Melting changes the structure: When ice melts, the crystalline structure breaks down, and the water molecules pack more closely together.

• Volume decreases: This closer packing results in a decrease in volume.

• Mass remains constant: The mass of the water remains the same during the phase change from ice to liquid water.

• Elements such as cast iron ice antimony bismuth and brass when melts their volume decreases these type of solids floats in their own fluid.

2. The variations in temperature from 0°C to 100°C with respect to time of two liquids P, Q are shown in the graph given below: [I.A.S. (Pre) 1995]

Which of the following statement is correct?

(a) During heating, liquid P has always warmer than Q.
(b) At no point of time during heating did the two liquids have the same temperature.
(c) P attained the temperature of 100°C faster than Q.
(d) Q attained the temperature of 100°C faster than P.

Correct Answer: (d) Q attained the temperature of 100°C faster than P.

Solution:In above diagram, P denotes a straight line, while point Q denotes a curved line. It is clear that Q attained the temperature of 100°C quicker than P.

3. What is the use of thermostat ? [M.P.P.C.S.(PRE) 2005]

(a) to measure the temperature.
(b) to increase the temperature.
(c) to maintain the temperature.
(d) to convert heat energy into electricity.

Correct Answer: (c) to maintain the temperature.

Solution:Thermostat is a device that automatically regulates temperature. It helps to save energy/power.

4. Thermostat is related to : [U.P.P.C.S.(pre) 1993]

(a) humidity
(b) temperature
(c) air
(d) clouds

Correct Answer: (b) temperature

Solution:Thermostat is a device that automatically regulates temperature. It helps to save energy/power.

5. Thermostat is a device which : [U.P.P.C.S.(pre) 2007]

(a) measure heat.
(b) measure temperature.
(c) automatically regulates the temperature of a system.
(d) automatically regulates pressure of a system.

Correct Answer: (c) automatically regulates the temperature of a system.

Solution:Thermostat is a device that automatically regulates temperature or provide a signal used by another device to regulate temperature.

6. Thermostat ........................ is a mean of keeping stable ? [Chhattisgarh P.C.S.(PRE) 2003]

(a) current
(b) temperature
(c) pressure
(d) heat radiation

Correct Answer: (b) temperature

Solution:Thermostat is a device that automatically regulates temperature or provide a signal used by another device to regulate temperature.

7. What is the function of the thermostat of a refrigerator ? [U.P.P.C.S.(pre) 1996]

(a) to lower the temperature.
(b) to increase the freezing point.
(c) to maintain constant temperature.
(d) to decrease the melting point.

Correct Answer: (c) to maintain constant temperature.

Solution:Thermostat is a device that automatically regulates temperature or provide a signal used by another device to regulate temperature.

8. The safest temperature for keeping food fresh in a refrigerator is: [U.P.P.C.S. (PRE) 2007]

(a) 4°C
(b) 8°C
(c) 0°C
(d) 10°C

Correct Answer: (a) 4°C

Solution:Refrigerator temperatures do not destroy pathogenic or spoilage microorganisms. The lower temperature slows the growth of microorganisms already in the food. Some bacteria grow most rapidly in the range of temperature between 40° and 140°F, the "Danger Zone". Thus it is necessary to make sure that the refrigerator is maintaining the recommended temperature of 35 to 40 degree F or below. According to international standards, the recommended temperature of the refrigerator is 36°F to 38°F (1.7°C to 3.3°C). Thus option (a) is correct.

9. When soggy biscuits are kept inside the fridge for sometime they become crisp because: [U.P.P.C.S. (Pre) 2009]

(a) Cooling releases extra moisture.
(b) Humidity inside the fridge is low and extra moisture is absorbed.
(c) Humidity inside the fridge is high and extra moisture is absorbed.
(d) Pressure inside the fridge is high and help in releasing extra moisture.

Correct Answer: (b) Humidity inside the fridge is low and extra moisture is absorbed.

Solution:

Low Humidity in Refrigerators:Refrigerators are designed to remove moisture from the air inside to prevent food spoilage. This results in a very dry environment.
Moisture Absorption:Soggy biscuits contain excess moisture. The dry air within the refrigerator acts like a sponge, drawing this moisture out of the biscuits.
Result: Crispness: As the biscuits lose their excess moisture, they regain their crisp texture.

10. Assertion (A): A piece of ice added to the drink, cools it. Reason (R) : Ice takes latent heat from the drink for melting resulting in the cooling of the drink. [U.P. Lower Sub (pre) 2009]

Select the correct answer using the codes given below:

(a) Both (A) and (R) are true, and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true, but (R) is not the correct explanation of (A).
(c) (A) is true, but (R) is false.
(d) (A) is false, but (R) is true.

Correct Answer: (a) Both (A) and (R) are true, and (R) is the correct explanation of (A).

Solution:Heat transmits from hot body to cold body. Ice takes latent heat from the drink to melt and makes drink cooler.

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Heat and Thermodynamics part-(2)