Conceptual question for Thermodynamics Part 4

PART 4

1. The amount of energy radiated by a body depends on
a.The nature of the surface
b. The area of the surface
c. Temperature of the surface
d. all the above

2. The wavelenght of the radiation emitted by the body depends on
a.The nature of the surface
b. The area of the surface
c. Temperature of the surface
d. all the above

3.A solid sphere and a hollow sphere of same material and size are heated to the same temperature and allowed to cool in the same surounding.If the temperature diffrence between the sphere and surrounding is T.then
a. Both sphere will cool at the same rate for all values of T
b Hollow sphere will cool faster for all values of T
c. Solid sphere will cool faster for all values of T
d. Both sphere will cool at the same rate for small values of T

4. An ideal black body is thrown in the furnace.It is observed that
a. Intially it is the darkest body and at later times the brightest
b. it is the darkest body all the times
c. It cannot be distinguish at all the times
d. Intially it is the darkest body and at later times It cannot be distinguish


5.In which of the following process,convection does not takes place
a. sea and land breeze
b.boiling of the water
c.heating air around the furnace
d.warming of glass of bulb due to filament

6.One end of a metal rod is kept in a furnace.In steady state,the temperature of the rod
a. Increase
b decrease
c. remains constant
d is non uniform

7 what is true for black body
a e=a=1
b emit radiation and absorb radiation
c. refract radiation
d none of the above

8.which one is true about thermal radiation
a. all bodies emit radiation at all temperature
b. Good reflectors are good emitters of thermal radiation
c. Thermal radiation travel in free space with the velocit of light
d. Thermal radiation are not reflected from the mirror

Conceptual question for Thermodynamics

PART 3

1.In a given process of an ideal gas,dW=0 and dQ<0 ,then for a gas
a.dT <0
b. dV>0
c.dP=0
d. dT>0

2.what is true for a free expansion process
a. dW=0
b. dQ=0
c. dU=0
d. all the above

3. Consider the following two statement
A.If heat is added to the system,it temperature must increase
B.If dW >0 then dV >0
a A & B both are correct
b A is correct only
c. B is correct only
d A &B both are wrong

4.what is true of Isothermal process
a. dT>0
b. dT=0
c. dQ=dW
d. none of the above

5. if dU=-dW for a process,the process is
a. Adiabatic
b. Isothermal
c. Isobaric
d. None of the abobe

6.What is true of a cyclic process
a.ΔQ=ΔW
b ΔU=0
c.ΔU >0
d None of the above

7. An ideal gas is taken from state A(P,V) to state B(P/2,2V) along a straight line path in P-V diagram.Select the correct statement from the following
a.The workdone by the gas in process A to B exceeds the work that would be done by it if the system were taken from A to B along a isotherm
b.in the T-V diagram ,the path AB becomes a part of a parabola,
c. In the P-T diagram,the path becomes a part of a parabola
d.In going from A to B,the temperature T of the gas first increase to a maximum and then decrease

8.Let W₁,W₂ are the workdone in the two process A & B by an ideal gas.ΔT_A=ΔT_B. Let C_A and C_B are the molar heat capacities in two process
Also W₁ > W₂. whic of the following is correct
a.C_A=C_B
b.C_A < C_B
c. C_A > C_B
d None of the above.

9.which of the following is correct
a. Molar heat capacity is 0 for PV^y=Constant
b. Molar heat capacity is infinity in adiabatic process
c. Internal energy does not change in Isothermal Process
d. All the above

10.An ideal gas is taken from state A(P₁,V₁) to state B(P₂,V₂) by two method X & Y..which of the following is correct
a.ΔQ₁-ΔW₁=ΔQ₂-ΔW₂
b.ΔU₁=ΔU₂
c. ΔQ₁+ΔW₁=ΔQ₂+ΔW₂
d. None of the above

Conceptual Question of Thermodynamics

PART 2


1.which one is not the assumption in kinetic theory of gases
a.the molecules of the gas are in continual random motion
b. The molecules interact during the collison
c. The molecules are tiny hard sphere undergoing inelastic collision
d. The collison are of short duration

2. There are two statement
A. Equal volumes of all gases at the same temperature T and pressure P contain an equal no of Molecules
B.the no of molecules in one mole of any gas is 6.0255 * 10²².
which one of the following is correct
a. A and B both
b. A only
c B only
d. A and B both are incorrect

3.There are two statement about Ideal gases
A. The V_rms of gas molecules depends on the mass of the gas molecule and the temperature
B. The V_rms is same for all the gases at the same temperature
which one of the following is correct
a. A and B both
b. A only
c B only
d. A and B both are incorrect

4.Choose the correct statement of the following
a. The pressure of the gas is equal to the total kinetic energy of the molecules in a unit volume of the gas
b. The product of pressure and volume of the gas is always constant
c. The average kinetic energy of molecule of the gas is proportional to its absolute temperature
d. The average kinetic energy of molecule of the gas is proportional to the square root of its absolute temperature

5..which one is true according Vander Waal gas equation
a. The attractive forces between the molecules is not negligible
b Volume of the molecules is negligible as compared to the volume occupied by the gas
c. Volume of the molecules is not negligible as compared to the volume occupied by the gas
d. The attractive forces between the molecules is negligible

Solution

Solution of PART 1
1. (a)
There was no restriction for it expansion.So no tensile or compressive force developed.Longitudinal strains happens only when tensile or compressive force developed in the rod.So answer a

2.(c)
3.(d)
4.(c)
5. (a),(b)
6.(b)
7.(a),(c)
Due to thermal expansion,the diameter of the disc as well of the hole will increase.therefore the moment of inertia will increase resulting in a increase in the angular speed.

Solution of PART 2
1 (c)
2. (b)
3. (b)
4.(c)
5. (a),(c)

Solution of PART 3
1. (a)
dU=dQ-dW or dU=dQ as dQ is negative & dW=o
so dU is negative .dU <0 now dU =nC_vdT
so nC_vdT <0 or dT<0
2.(d)
3.(c) as dW=pdV so if dW> 0 the dV >0
4. (b),(c) as temperature is constant.
5. (a)
6. (a),(b)
7. (a),(b),(d)
8. (c)
9.(a),(c)
10. (a),(b)


Solution of PART 4
1. (d)
2. (c)
3. (b)
4. (a)
5. (d)
6. (d)
7. (a),(b)
8.(d)

Conceptual questions of Thermodynamics

PART 1

1. A rod of length L having coefficent of Linear expansion α is lying freely on the floor.it is heated so that temperature changes by ΔT .Find the longitidunal strain developed in the rod
a. 0
b. αΔT
c. -αΔT
d. none of the above

2.if a is coefficent of Linear expansion,b coefficent of areal expansion,c coefficent of Volume expansion.Which of the following is true
a. b=2a
b. c=3a
c. b=3a
d. a=2b

3.which is of them is not used as the measurable properties in thermometer?
a.Resistance of platinum ire
b.Constant volume of gas
c.Contant pressure of gas
d.None of the above

4.when a solid metalic sphere is heated.the largest percentage increase occurs in its
a.Diameter
b. Surface area
c. Volume
d. density

5.the density of the liquid depends upon
a. Nature of the liquid
b. Temperature of the liquid
c. Volume of the liquid
d. Mass of the liquid

6. A metallic sphere has a cavity of diameter D at its center.If the sphere is heated,the diameter of the . cavity will
a. Decrease
b. Increase
c. Remain unchanged
d. none of the above

7.A metallic circular disc having a circular hole at its center rotates about it axis passing through the center and perpendicular to it plane.when the disc is heated
a. Its speed will decrease
b. Diameter will increase
c. Moment of inertia will increase
d. its speed will increase

Quick Recap of Thermodynamics

Notes for Examination


Temperature

Relation between Celsius and fahrenhite scale is

T_F=9/5 T_C + 32°

T_F - Fahrenhite Temperature
T_C - Celsius Temperature

Relation between Celsius and kelvin scale is
T_C = T_K - 273.15 K


T_K - Temperature in Kelvin
T_C - Temperature in celsius


- If R₀ & R₁₀₀ are resistance of metak wire at ice and steam point resp then temp t can be defined corresponding to resistance R_T as follows

T =	(RT-R0)*100
	R100-R0

- The pressure,volume and temperature in kelvin of such gases obey the equation
PV=nRT ----(1)



Thermal expansion
ΔL=αLΔT


Specific Heat Capacity

c =	`Q
	nΔT

Gas Laws
Boyles Law: PV=constant
Charles Law : V/T=constant
Dalton Law of Partial Pressure: P=P₁ + P₂ +P₃
Root mean Square VelocityV_rms=√3RT/M
Mean Square Velocity
V_m=√8RT/&#960M
Average Velocity
V=√2RT/M
Also
V_rms > V_m > V

Average kinetic Energy of Gas=3/2nRT


First law of Thermodynamics

ΔU=Q-W


Gas Processes

Isothermal Process : PV=constant ,ΔU=0,Q=W,Molar Specific Heat=infinity
Adaibatic Process : PV^y=constant,Q=0,ΔU=-W,Molar Specific Heat=zero
Polytropic Process : PVⁿ=constant,Molar Specific Heat=R/y-1 + R/1-n
Volume Constant : P/T=constant W=0,ΔU=Q,Molar Specific Heat=C_v
Pressure Constant : V/T=constant ΔU=Q-W ,Molar Specific Heat=C_P

Internal energy depends on Temperature.
So for same temperature change ΔT
nC_vΔT=Q₁-W₁=Q₂-W₂=Q₃-W₃

Molar Specfic Heat Capacity of any process is given by

C=C_v + Pdv/ndT where n is no of moles of the gas

Workdone by Gas= ∫PdV



Heat Conduction

Q=-KAdT/dx

Wein displacement lawλT⁴=Constant

Stefan's Law
Q=eσT⁴

Newton law of Cooling

dT/dx=b(T-T_s)

Thermal Expansion

- Increase in dimension of body due to increase in temperature is call thermal expansion
- Most of the solid material expand when heated

-Consider a rod of length L then for small change in temperature ΔT,the fractional change in length ΔL/L is directly propertional to ΔT
ΔL/L=αΔT --(2)
or ΔL=αLΔT --(3)
- constant α characterizes the thermal expansion properties of a particulaqr material and it is known as coefficient of linear expansion.
- for materials having no prefential direction,every linear dimension changes according to equation (3) and L could equally well represent the thickness of the rod,side lenght of the square sheet etc
-Normally metals expand more and have high value of α
- Agian consider the intial surface area A of any surface .Now when the temperature of the body is increases by ΔT ,the increase in surface area is given by
ΔA=α_AAΔT ----(4)
where α_A is the coefficient of area expansion
-Similary we can define coefficient of volume expansion as fractional change in volume ΔV/V of a substance for a temperature change ΔT

as ΔV=α_VVΔT ----(5)
- K^-1 is the unit of these coefficents expansions
- These three coefficent are not strictly constant for a substance and these value is depends on temperature range in which they are measured.

Relation between volume and linear coefficient of expansion for solid materail: Consider a solid parallopide with dimension L₁,L₂ and L₃
then volume is
V= L₁L₂L₃
when temperature increase by a amount ΔT then each linear dimension changes and then new volume is
V+ΔV=L₁L₂L₃(1+α_L )
V+ΔV=V(1+α_LΔT)³
V+ΔV=V(1+3α_LΔT+3α_L²ΔT²+α_L³ΔT³)
if ΔT is small the higher order can be neglected.Thus we find
V+ΔV=V(1+3α_LΔT)
ΔV=3α_LVΔT
Comparing this with equation (5) we find
α_V=3α_L