Tag: behaviour of perfect gas and kinetic theory of gases

Questions Related to behaviour of perfect gas and kinetic theory of gases

Multiple choice physics the kinetic model of matter gases and the kinetic theory concept of ideal gas and state equation of ideal gas behaviour of perfect gas and kinetic theory of gases

An air bubble rises from the bottom of a deep lake the radius of the air bubble near the surface is 'r'. Choose the appropriate radius of the air bubble.

a) r/2 at depth 30m 

b) r/2 at depth 70m

c) r/3 at depth 140m 

d) r/3 at depth 260m

  1. a,c

  2. a,d

  3. b,c

  4. b,d

Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

At a depth of h water pressure will be
${P} _{h} = {P} _{a} + \rho gh$                eq(1)
where 
$\rho  =1000 kg/{m}^{3}$
$g  = 9.81 m/{s}^{2} $
$h = \text{depth  of  water  bubble}$
${P} _{a} = {10}^{5}Pa$

initially bubble is below water at h, so
${P} _{1} = {P} _{h}$
finally it rises to surface of lake so
${P} _{2} = {P} _{a}$

we assume that temperature is constant when it is rising from bottom to surface
by ideal gas equation
${P} _{1}{V} _{1} = {P} _{2}{V} _{2}$

volume can be written as $V = \dfrac{4}{3}\pi {r}^{3}$
where r is radius.
${P} _{h} \times \dfrac{4}{3}\pi {r} _{h}^{3} = {P} _{a} \times \dfrac{4}{3}\pi {r} _{s}^{3}$
${r} _{h} = {(\dfrac{{P} _{a}}{{P} _{h}})}^{1/3} r$
${r} _{h} = \dfrac{r}{{(\frac{{P} _{h}}{{P} _{a}})}^{1/3}}$
by eq(1)
${r} _{h} = \dfrac{r}{{(\dfrac{{P} _{a} +  \rho gh}{{P} _{a}})}^{1/3}}$
${r} _{h} = \dfrac{r}{{(1 + 0.0981h)}^{1/3}}$              eq(2)

(a) at depth 30m
h = 30m
put h=30 in eq(2)
${r} _{h} = \dfrac{r}{1.5}$
false

(b) at depth 70m
h = 70m
put h=70 in eq(2)
${r} _{h} = \dfrac{r}{2}$
true

(c) at depth 140m
h = 140m
put h=140 in eq(2)
${r} _{h} = \dfrac{r}{2.4}$
false

(d) at depth 260m
h = 260m
put h=260 in eq(2)
${r} _{h} = \frac{r}{3}$
true

Answer is D.

Multiple choice physics the kinetic model of matter gases and the kinetic theory concept of ideal gas and state equation of ideal gas behaviour of perfect gas and kinetic theory of gases

A barometer reads 75 cm of mercury. When 2.0cm$^{3}$ of air at atmospheric pressure is introduced into space above the mercury level, the volume of the space becomes 50cm$^{3}$. The length by which the mercury column descends is

  1. 3 cm of Hg

  2. 6 cm of Hg

  3. 30 cm of Hg

  4. 10 cm of Hg

Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Let the new pressure inside be $P$ after air introduced.

For the air,
$P _1V _1=P _2V _2$
$\implies P(50)=(75)(2)$
$\implies P=3\ cm\  of\ Hg$

Multiple choice physics the kinetic model of matter gases and the kinetic theory concept of ideal gas and state equation of ideal gas behaviour of perfect gas and kinetic theory of gases

Boyle's law is applicable when

a) temperature is constant

b) gas is at high temperature and low pressure

c) the vessel enclosing the gas is good conductor

d) the process is isothermal

  1. a & b

  2. b,c & d

  3. a,b & c

  4. a,b,c & d

Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

(a) Temperature must be constant to apply boyle's law
(b)From vanderwaal's equation when non idealities of a gas is undertaken then we can apply boyle's only when temperture is high and pressure is low
(c)Vessel enclosing must be a good conductor so there is no any possibilities of adiabatic process
(d) Temperature must be constant therefore, process must be isothermal
Hence all are correct
Hence option(D)

Multiple choice physics behaviour of perfect gas and kinetic theory of gases degree of freedom: law of equipartition of energy law of equipartition of energy law of equipartition of energy and mean free path

How many degrees of freedom the gas molecules have if under STP the gas density $\rho = 1.3 kg/m^3$ and the velocity of sound propagation in it is $330 ms^{-1}$?

  1. $3$

  2. $5$

  3. $7$

  4. $8$

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Using v = sqrt(gamma * P / rho) and P = (rho/M)RT, we find gamma. Since v = 330 m/s, rho = 1.3 kg/m^3, and P = 1.013e5 Pa, gamma = v^2 * rho / P = 1.71. However, for standard gases, gamma = 1 + 2/f. With gamma = 1.4 (diatomic), f = 5. The provided data yields gamma approx 1.4, corresponding to f = 5.

Multiple choice physics behaviour of perfect gas and kinetic theory of gases degree of freedom: law of equipartition of energy law of equipartition of energy law of equipartition of energy and mean free path

At room temperature (27$^0$ C) the rms speed of the moleculesof certain diatomic gas is found to be 1920 ms$^{-1}$ then the molecule is:

  1. $H _2$

  2. $F _2$

  3. $O _2$

  4. $Cl _2$

Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Let the room temperature is $T = 27^0C=27+273=300K$
Now, $V _{rms}=\sqrt{\dfrac{3RT}{m}}$
$\Rightarrow M=\dfrac{3RT}{V _{rms}^2}$
By putting the value we get,
$M=\dfrac{3\times8.314\times300}{1920^2}=2\times10^{-3}kg=2g$
Thus, it is an Hydrogen.
Multiple choice physics behaviour of perfect gas and kinetic theory of gases degree of freedom: law of equipartition of energy law of equipartition of energy law of equipartition of energy and mean free path

If temperature of body increases by 10%, then increase in radiated energy of the body is :

  1. 10 %

  2. 40 %

  3. 46 %

  4. 1000 %

Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

According to the Stefan-Boltzmann law, radiated energy E is proportional to T^4. If T increases by 10%, T_new = 1.1T. Then E_new = (1.1)^4 * E = 1.4641 * E. The increase is 46.41%.

Multiple choice physics behaviour of perfect gas and kinetic theory of gases degree of freedom: law of equipartition of energy law of equipartition of energy law of equipartition of energy and mean free path

The law of equipartition of energy was given by :

  1. Claussius

  2. Maxwell

  3. Boltzmann

  4. Carnot

Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The law is given by Claussius which states that for any dynamical system in a thermal equilibrium, the total energy is equally divided among the degrees of freedom.

Multiple choice physics behaviour of perfect gas and kinetic theory of gases degree of freedom: law of equipartition of energy law of equipartition of energy law of equipartition of energy and mean free path

The value of $\gamma$ for gas X is 1.66, then x is :

  1. Ne

  2. O$ _3$

  3. N$ _2$

  4. H$ _2$

Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Given that value of gamma is 1.66 i.e $\dfrac{5}{3}$ which implies that it is a monoatomic gas, and Neon (Ne) is the only monoatomic gas among the given options.

Multiple choice physics behaviour of perfect gas and kinetic theory of gases degree of freedom: law of equipartition of energy law of equipartition of energy law of equipartition of energy and mean free path

An ant is moving on a plane horizontal surface. The number of degrees of freedom of the ant will be

  1. 1

  2. 2

  3. 3

  4. 6

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Degrees of freedom represent the number of independent coordinates required to specify the position of an object. An ant on a 2D plane requires two coordinates (x, y).

Multiple choice physics behaviour of perfect gas and kinetic theory of gases degree of freedom: law of equipartition of energy law of equipartition of energy law of equipartition of energy and mean free path

Gas exerts pressure on the walls of container because the molecules-

  1. Are loosing the kinetic energy

  2. Are getting stuck to the walls

  3. Are transferring their momentum to walls

  4. Are accelerated toward walls.

Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Gas molecules are in random motion having some momentum and while colliding with the walls they transfer their momentum to the walls and this collective transfer of momentum from all the molecules to the walls appears as pressure exerted by gas on the container wall.