Molecular Physics | Thermodynamics Answers

7 Which of these determines whether or not heat flows in a system?
average speed of the consituent particles of the system
pressure difference between parts of the system
degree of hotness or coolness of the system
temperature difference between parts of the system

8 Which of the following is NOT true about conduction as a means of heat transfer?
transfer of heat occurs through sucessive collisions of the atoms or molecules
the average kinetic energy of the atoms or molecules is greater in the hot object than in the cold object
the transfer process requires a material medium for it to take place
there is net translational motion of the atoms or molecules from their mean equilibrium positions

3 A scientist uses a scale Y for measuring temperature. In this scale, pure water melts at
10oY
and boils at
130oY
at standard atmospheric pressure. The scientist measures the temperature at which sodium melts to be
127oY
. Express this temperature in degrees Celsius
97.5oC
102.6oC
38.6oC
196.6oC

4 When the junctions of two dissimilar metals are maintained at different temperatures an electromotive force is is set up in the circuit of which these junctions are part. A pair of juntions of this kind and the effect are known respectively as
thermistor and Peltier effect
resistance thermometer and Joule effect
pyrometer and Joule effect
thermocouple and Seebeck effect

18 An engine absorbs 2000J of heat from a hot reservoir and expels 750J to a cold reservoir during each operating cycle. How much work is done during the cycle?
1250J
750J
2000J
350J

19 An engine absorbs 2000J of heat from a hot reservoir and expels 750J to a cold reservoir during each operating cycle. What is the power output of the engine if each cycle lasts for 0.5 seconds?
750W
1750W
3000W
2500W

20 The first law of thermodynamics is a restatement of which of these laws?
conservation of charge
conservation of momentum
conservation of entropy
onservation of energy

15 In which of the following phenomena is surface tension important?
the floating of a boat in water
the floating of a steel wire in water
the floating of a ballon in air
the floating of a plastic sphere in water

16 Which of the following substances has the highest viscosity at room temperature?
Water
kerosine
palm oil
alcohol

17 An engine absorbs 2000J of heat from a hot reservoir and expels 750J to a cold reservoir during each operating cycle. What is the efficiency of the engine?
50%
62.5%
74.2%
85.6%

8 If the volume of a gas is
500cm3
at
127o
C and 380mm of mercury, calculate the volume of this gas at s.t.p
115cm3
128.7cm3
149.2cm3
170.6cm3

9 The mechanism of heat transfer from one point to another through vibration of the molecules of the medium is called -------------
convection
conduction
radiation
diffusion

5 Thermal expansion of a solid material depends on the following EXCEPT
the nature of the material making up the solid
the range of the temperature change
the initial dimensions of the solid
average translational motion of constituent atoms of the material

6 One of these is NOT a basic assumption of kinetic theory of ideal gases
a gas consist of a large number of molecules
the attraction between the molecules is negligible
the kinetic energy of the molecules is changing continuously
the gas molecules are in a state of continuous random motion

7 One of these is an example of thermal radiation detector
bolometer
thermometer
thermal rod
thermal glass

3 Calculate the work done against external atmospheric pressure when 1 g of water changes to
1672cm3
of steam. Take the atmospheric pressure as
1.013×105Nm−2
169.3 J
342.4 J
226.2 J
143.5 J

4 An electric kettle contains 1.5 kg of water at
100oC
and powered by a 2.0 kW electric element. If the thermostat of the kettle fails to operate, approximately how long will it take for the kettle boil dry? (Take the specific latent heat of vaporization of water as
2000kJkg−1)
500s
1000s
1500s
3000s

Question: A small oxygen tank at a Guage pressure of 125 atm has a volume of 6.88l at 21.0 degree Celsius. If an athlete breathes oxygen from this tank at the rate of 8.50 liter per minute when measured at atmospheric pressure and the temperature remains constant at 21.0 degree Celsius how long will the tank last before it is empty

In an experiment to verify Newton's law of cooling, the temperature of hot water in a calorimeter
T/oC
is plotted against time t/min. Which of the following is true about the graph?
the graph is linear and parallel to the T-axis
the slope of the graph is positive
the slope of the graph is negative
the graph is hyperbola

A student walking to class on a cold day (T=0 C) finds a silver ring with an inner diameter of D=1.8 cm. The silver has a coefficient of expansion of a=18.7 x 10^-6

a) Input an expression for the rings inner diameter Dh when the student warms it up to their body temperature, Tb.

b)What is the change in diameter in mm if Tb = 37 C