JEE Main Physics - Heat and Thermodynamics
Exam Duration: 60 Mins Total Questions : 30
Choose the INCORRECT statement :
- (a)
A cavity inside a solid ball expands on heating
- (b)
The saturated vapour pressure of water at 100\(?\) is 0.76 m Hg
- (c)
The relative humidity is 110%
- (d)
Heat waves can pass through vacuum
At 27\(?\) and a pressure of 1.0 \(\times\) 105 Pa, an ideal gas has a volume of 0.04 m3. It is heated at constant pressure until its volume increases to 0.05 m3. Its mass is 45 g, its molar mass is 28 g and its molar heat capacity at constant volume is 0.6 J mol-1 K-1. The total heat given to the gas is
- (a)
72 J
- (b)
1000 J
- (c)
928 J
- (d)
1072 J
A body takes T minutes to cool from 62\(?\) to 61\(?\) when the surrounding temperature is 30\(?\). The time taken by the body to cool from 46\(?\) to 45\(?\) is
- (a)
greater than T minutes
- (b)
equal to T minutes
- (c)
less than T minutes
- (d)
equal to T/2 minutes
When 110 J of heat is added to a gaseous system, internal energy increases by 40 J; the amount of work done is:
- (a)
150 J
- (b)
70 J
- (c)
110 J
- (d)
40 J
By opening the door of a refrigerator inside a closed room:
- (a)
you can cool the room to a certain degree
- (b)
you can cool it to the temperature inside the refrigerator
- (c)
you ultimately warm the room slightly
- (d)
you can neither cool nor warm the room
A reversible engine converts one-sixth of the heat input into work. When the temperature of the sink is reduced by 62°C, the efficiency of the engine is doubled. The temperatures of the source and sink are:
- (a)
99°C, 37°C
- (b)
80°C, 37°C
- (c)
95°C, 37°C
- (d)
90°C, 37°C
We consider a thermodynamic system. If \(\Delta\)U represents the increase in its internal energy and W the work done by the system, which of the following statements is true?
- (a)
\(\Delta\)U = -W is an isothermal process
- (b)
\(\Delta\)U = + W is an isothermal process
- (c)
\(\Delta\)U = -W is an adiabatic process
- (d)
\(\Delta\)U = + W is an adiabatic process
The temperatures of inside and outside of a refrigerator are 273 K and 303 K respectively. Assuming that the refrigerator cycle is reversible, for every joule of work done, the heat delivered to the surroundings will be nearly:
- (a)
10 J
- (b)
20 J
- (c)
30 J
- (d)
50 J
The isochoric modulus of elasticity is:
- (a)
equal to isentropic modulus of elasticity
- (b)
equal to isothermal modulus of elasticity
- (c)
zero
- (d)
infinity
70 calories of heat are required to raise the temperature of 2 moles of an ideal gas at constant pressure from 30°C to 35°C. The amount of heat required to raise the temperature of the same gas through same range (30°C to 35°C) at constant volume is:
- (a)
30 cal
- (b)
50 cal
- (c)
70 cal
- (d)
90 cal
The gas law \(\frac { PV }{ T } \) = constant true for:
- (a)
isothermal changes only
- (b)
adiabatic changes only
- (c)
both isothermal and adiabatic changes
- (d)
neither for isothermal nor for adiabatic changes
At what temperature, the Fahrenheit and the Celsius scales will give numerically equal (but opposite in sign) values?
- (a)
- 40°F and 40°C
- (b)
11.43°F and -11.43°C
- (c)
-11. 43°F and + 11. 43°C
- (d)
+40°F and - 40°C
The densities of a liquid in g/cm3 at 0° C and 100° Care respectively 1.0127 and 1. A specific gravity bottle is filled with 300 g of the liquid at O°Cupto the rim and it is heated to 100°C. Then the mass of the liquid expelled (in grams) is: (coefficient of linear expansion of glass = 9 x 10-6/° C )
- (a)
\({3\over 1.01}\)
- (b)
\({3\over 10.1}\)
- (c)
\({3.81\over 1.0127}\)
- (d)
\({3.81\over 0.0127}\)
If for hydrogenCp -C\(\upsilon\) =mandfornitrogenCp -C\(\upsilon\) =n, where Cp and C\(\upsilon\) refer to specific heats per unit mass respectively at constant pressure and constant volume, the relation between m and n is: (Molecular weight of hydrogen = 2 and molecular weight of nitrogen = 14)
- (a)
n=14m
- (b)
n=7m
- (c)
m= 7n
- (d)
m= 14n
Which of the following engines have 100% efficiency?
- (a)
Auto engine
- (b)
Internal combustion engine
- (c)
Petrol engine
- (d)
Carnot engine
A gas (\(\gamma\)= 1.3) is at a pressure 105 N/m2 in a vessel surrounded by non-conducting medium and having a non-conducting piston. The volume becomes half of its initial value by suddenly pressing the piston. Then, calculate the pressure afterwards:
- (a)
20.7 x 105 N/m2
- (b)
21.3 x 105 N/m2
- (c)
21.4 x 105 N/m2
- (d)
none of these
If 150 J of heat is added to a system and the work done by the system is 110 kl, then change in internal energy will be
- (a)
260 J
- (b)
150 J
- (c)
110 J
- (d)
40 J
An ideal gas is compressed isothermally until its pressure is doubled and then allowed to expand adiabatically to regain its original volume (\(\gamma\) = 1.4 and 2-1.4= 0.38). The ratio of the final to initial pressure is:
- (a)
0.76 : 1
- (b)
- (c)
- (d)
Three samples of the same gas A, Band C(\(\gamma\)= 3/2) have initially equal volume. Now the volume of each sample is doubled. The process is adiabatic for A isobaric for Band isothermal for C. If the final pressures are equal for all the three samples, the ratio of their initial pressures is:
- (a)
2\(\sqrt{2}\) : 2: 1
- (b)
2\(\sqrt{2}\) : 1: 2
- (c)
\(\sqrt{2}\):1:2
- (d)
2:1:\(\sqrt{2}\)
A vertical column 50 em long at 50° e balances another column of same liquid 60 em long at 100° C. The coefficient of absolute expansion of the liquid is:
- (a)
0.005/° C
- (b)
0.0005/° C
- (c)
0.002/° C
- (d)
0.0002/° C
A g!ls is suddenly expanded such that its final volume becomes 3 times its initial volume. If the specific heat at constant volume of the gas is 2R, then the ratio of initial to final pressure is nearly equal to:
- (a)
5
- (b)
6.5
- (c)
7
- (d)
3.5
During an adiabatic process, the cube of the pressure is found to be inversely proportional to the fourth power ofthe volume. Then, the ratio of specific heats is:
- (a)
1
- (b)
1.33
- (c)
1.67
- (d)
1.4
A metal sphere is suspended from one pan of a sensitive balance and is immersed completely in water The other pan
carries weights to balance the immersed sphere. The water is then heated to a high temperature and the weights may have 10 be removed or added to balance the sphere immersed in hot water. Which one of the following observations is correct?
- (a)
Sphere expands, water is displaced; weights are to be
removed. - (b)
Sphere expands, water is displaced; weights are ro be
added. - (c)
Water expands, sphere sinks; weights are to be added.
- (d)
Water expands, sphere sinks; weights arc to be removed.
A Carnot engine whose efficiency is 40%, receives heat at 500 K. If the efficiency is to be 50%, the source temperature for the same exhaust temperature is
- (a)
900 K
- (b)
600 K
- (c)
700 K
- (d)
800 K
- (e)
550 K
If the temperatures of source and sink of a Carnot engine having efficiency 11 are each decreased by 100 K, then the efficiency:
- (a)
remains constant
- (b)
becomes 1
- (c)
decreases
- (d)
increases
- (e)
becomes zero