Physics - Heat and Thermodynamics
Exam Duration: 45 Mins Total Questions : 30
A 300-g piece of tin is placed on a large block of ice, and this system is thermally isolated from its surroundings. As the tin cools to the temperature of the block (0\(?\)), 18.0 g of ice melts. Original temperature of tin was [specific heat of tin = 0.05 cal g-1 \(?\)-1]
- (a)
96\(?\)
- (b)
48\(?\)
- (c)
40\(?\)
- (d)
110\(?\)
A themally insulated vessel contains an ideal gas of molecular mass M and ratio of specific heats \(\gamma\). It is moving with speed v and its suddenly brought to rest. Assuming no heat is lost to the surroundings, its temperature increase by
- (a)
\({(\gamma-1)\over2\gamma R}Mv^2K\)
- (b)
\({\gamma Mv^2\over 2R}K\)
- (c)
\({(\gamma-1)\over2R}Mv^2K\)
- (d)
\({(\gamma-1)\over2(\gamma+1)R}Mv^2K\)
When heat is added to a system, which of the following is not possible?
- (a)
Internal energy of the system increases
- (b)
Work is done by the system
- (c)
Neither internal energy increases nor work is done by the system
- (d)
Internal energy increases and also work is done by the system
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
A polyatomic gas with n degrees of freedom has a mean kinetic energy per molecule given by:
- (a)
\(\frac{nKT}{N}\)
- (b)
\(\frac{nKT}{2N}\)
- (c)
\(\frac{nKT}{2}\)
- (d)
\(\frac{3KT}{2}\)
In an adiabatic process where in pressure is increased by \(\frac{2}{3}\)% if \(\frac { { C }_{ p } }{ { C }_{ v } } =\frac { 3 }{ 2 } \), then the volume decreases by about:
- (a)
\(\frac{4}{9}\)%
- (b)
\(\frac{2}{3}\)%
- (c)
4%
- (d)
\(\frac{9}{4}\)%
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
Pi, Vi and Pf, Vf are initial and final pressures and volumes of a gas in a thermodynamic process respectively. If PVn = constant, then the amount of work done is:
- (a)
minimum for n =\(\gamma\)
- (b)
minimum for n = 1
- (c)
minimum for n = 0
- (d)
minimum for n =1/\(\gamma\)
Two cylinders A and B fitted with pistons contain equal amounts of an ideal diatomic gas at 300 K. The piston of A is free to move while that of B is held fixed. The same amount of heat is given to the gas in each cylinder. Ifthe rise in temperature of the gas in A is 30 K, then the rise in temperature of the gas in B is:
- (a)
30K
- (b)
18K
- (c)
50K
- (d)
42K
Two identical containers A and B with frictionless pistons contain the same ideal gas at the same temperature and the same volume V. The mass of gas in A is mA and that in B is mB. The gas in each cylinder is now allowed to expand isothermally to the same final volume 2V. The changes in pressure in A and B are found to be \(\triangle\)P and 1.5 \(\triangle\)P respectively. Then:
- (a)
4mA = 9mB
- (b)
2mA = 3mB
- (c)
3mA = 2mB
- (d)
9mA = 4mB
Find the amount of work done to increase the temperature of one mole of ideal gas by 30oC, if it is expanding under the condition V \(\infty \) T2/3: (R = 8.31 J/mol-K)
- (a)
16.62 J
- (b)
166.2 J
- (c)
1662 J
- (d)
1.662 J
For an adiabatic expansion of a perfect gas, the value of \(\Delta\)P/P is equal to:
- (a)
\(\frac { \Delta V }{ V } \)
- (b)
\(\gamma \frac { \Delta V }{ V } \)
- (c)
\(-\gamma \frac { \Delta V }{ V } \)
- (d)
\(-{ \gamma }^{ 2 }\frac { \Delta V }{ V } \)
The relationship between saturated vapour pressure P and absolute temperature T is:
- (a)
log P = a + bT - c
- (b)
log P = a + bT - \(c\over T\)
- (c)
log P = a +\(T\over b\) - c
- (d)
log P = a +\(T\over b\) - cT
Maximum density of H2O is at the temperature
- (a)
32°F
- (b)
39.2°F
- (c)
42°F
- (d)
4°F
A centigrade and a Fahrenheit thermometer are dipped in boiling water. The water temperature is lowered until the Fahrenheit thermometer registers 140°. What is the fall in temperature as registered by the centigrade thermometer?
- (a)
30°
- (b)
40°
- (c)
60°
- (d)
80°
The resistance of a resistance thermometer has values 2.71 and 3.70 ohm at 100Cand 100°C. The temperature at which the resistance is 3.26 ohm is:
- (a)
40°C
- (b)
50°C
- (c)
60°C
- (d)
70°C
A pendulum clock keeps correct time at 20° C. The correction to be made during summer per day, where the average temperature is 40° e, will be:\(\left( \alpha ={ 10 }^{ -5 }/^{ o }C \right) \)
- (a)
5.64 sec
- (b)
6.64 sec
- (c)
7.64 sec
- (d)
8.64 sec
A clock with a metal pendulum beating seconds keeps correct time at 0° C. If it loses 12.5 seconds a day at 25° e, the coefficient oflinear expansion of metal of pendulum is:
- (a)
\(\frac { 1 }{ 86400 } { / }^{ o }C\)
- (b)
\(a\frac { 1 }{ 43200 } { / }^{ o }C\)
- (c)
\(\frac { 1 }{ 14400 } { / }^{ o }C\)
- (d)
\(\frac { 1 }{ 28800 } { / }^{ o }C\)
A brass rod and lead rod each 80 em long at ooe are clamped together at one end with their free ends coinciding. The separation of free ends of the rods if the system is
placed in a steam bath is:(\({ \alpha }_{ B }\) = 18 x 10- 6/oC and \({ \alpha }_{ L }\) = 28x 1O-6/0C)
- (a)
0.2 mm
- (b)
0.8 mm
- (c)
1.4 mm
- (d)
1.6 mm
Liquid is filled in a flask upto a certain point. When the flask is heated, the level of the liquid:
- (a)
immediately starts increasing
- (b)
initially falls and then rises
- (c)
rises abruptly
- (d)
falls abruptly
Two metal strips that constitute a thermostat must necessarily differ in their:
- (a)
mass
- (b)
length
- (c)
resistivity
- (d)
coefficient of linear expansion
A bar of iron is 10 em at 20° C. At 19° C it will be : (\(\alpha\) of iron = 11x 10-6/ oC)
- (a)
11x 10-6 cm longer
- (b)
11x 10-6 cm shorter
- (c)
11x 10-5 cm shorter
- (d)
11x 10-5 cm longer
A glass flask is filled upto a mark with 50 cc of mercury at 18° C. If the flask and contents are heated to 38° C, how much mercury will be above the mark? (\(\alpha\) for glass is 9 x 10-6/° C and coefficient of real expansion of mercury is 180x 10-6/° C)
- (a)
0.85 cc
- (b)
0.46 cc
- (c)
0.153 cc
- (d)
0.05 cc
A Carnot engine whose sink is at 300 K has an efficiency of 40%. By how much should the temperature of source be increased so as to increase its efficiency by 50% of original efficiency?
- (a)
380 K
- (b)
275 K
- (c)
325 K
- (d)
250 K
The volume of an ideal diatomic gas is doubled isothermally. The internal energy:
- (a)
doubles
- (b)
is halved
- (c)
increases four times
- (d)
remains unchanged
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