Heat and Thermodynamics part-(1)

41. The value of 50°C in the Fahrenheit scale is : [65th B.P.S.C. (PRE)(RE.EXAM) 2019]

Correct Answer: (b) 122°F

Solution:F=(9/5)×C+32
⇒F=(9/5)×50+32
⇒F=90+32⇒F=122
so the value of 50°C at Fahrenheit scale.

42. In cold countries, alcohol is preferred to mercury as a thermometric liquid because: [U.P.P.C.S.(pre) 1997]

(a) Alcohol has a lower freezing point.
(b) Alcohol is a better conductor of heat.
(c) Alcohol is cheaper than mercury.
(d) The world production of alcohol is greater than that of mercury.

Correct Answer: (a) Alcohol has a lower freezing point.

Solution:There are lots of reasons for using alcohol than mercury Ans. (b) thermometric liquids. Some alcohol has a very low freezing point of about-112°C and therefore is suitable to record very low temperature. Thus, in cold countries, alcohol is preferred to mercury as a thermometric liquid.

43. Which one of the following is used as an antifreeze for the automobile engines ? [U.P.P.C.S. (Spl.) (Pre) 2008 U.P. U.D.A./L.D.A. (Mains) 2010]

(a) Ethanol
(b) Ethylene glycol
(c) Methanol
(d) Propyl alcohol

Correct Answer: (b) Ethylene glycol

Solution:Ethylene glycol is an organic molecule most widely used a antifreeze in automobile engines and as an industrial solvent When it is mixed with water, the freezing point of the mixture is depressed, specifically a mixture of 60% ethylene glyco and 40% water freezes at -45°C. That is why water is not frozen in the engine of cold countries.

44. What is absolute zero temperature? [Jharkhand P.C.S. (PRE) 2010]

(a) The starting point of any temperature scale
(b) Theoretically the lowest possible temperature.
(c) The temperature at which the vapour of any liquid substance is condensed.
(d) The temperature at which all material are in vapour form.

Correct Answer: (b) Theoretically the lowest possible temperature.

Solution:Absolute zero is the lowest possible temperature at which point the atoms of a substance transmit no thermal energy.They are completely at rest .It is 0 on the kelvin scale which translate to -273.15 degree celsius.

45. Expansion during heating - [U.P.P.C.S.(pre) 2006]

(a) occurs only in solid.
(b) decrease the weight of the material.
(c) decrease the density of the material.
(d) occurs at the same rate from all the liquids and solids.

Correct Answer: (c) decrease the density of the material.

Solution:Density is defined as the ratio of the mass and the volume or mass per unit volume (density=mass/volume) as the temperature increases most of the materials expend or increase their volume this is the result in a decrease in density.

Heat and Thermodynamics part-(1)