# 462 - Physics Questions Answers

A gaseous mixture consists of 16g of helium and 16g of oxygen. the ratio Cp/Cv of the mixture is

(1) 1.59

(2) 1.62

(3) 1.4

(4) 1.54

**Asked By: HIMANSHU MITTAL**

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**Joshi sir comment**

16 gms He = 4 mole, 16 gms O_{2}= 1/2 mole

so total freedom n = [4(3) + 1/2(5)] / [4 + 1/2] = 3.22222 here 3 and 5 are freedoms for mono and di atomic gases

so γ = 1 + 2/3.2222222 = 1.621

A vessel of volume 0.3 m³ contains helium at 20.0°C. the average kinetic energy per molecule for the gas is

(1) 6.07 * 10^(-21) J

(2) 7.3 * 10³ J

(3) 14.6 * 10³ J

(4) 12.14 * 10^(-21) J

**Asked By: HIMANSHU MITTAL**

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**Joshi sir comment**

Use the formula 3/2 kT

k is boltzmann constant = 1.38* 10^{-23}

4 moles of an ideal monoatomic gas is mixed with 6 moles of a non reactive diatomic ideal gas. the molar heat capacity of the mixture at constant volume is (assume no vibration) nearly

(1) 27 J mol‾¹K‾¹

(2) 17 J mol‾¹K‾¹

(3) 7 J mol‾¹K‾¹

(4) 37 J mol‾¹K‾¹

**Asked By: HIMANSHU MITTAL**

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**Joshi sir comment**

at constant volume work done = 0

degree of freedom = 4(3) + 6(5) / 4 + 6 = 12+30/10 = 4.2 so γ = 1 + (2/4.2)

so molar heat capacity = R/(γ-1)

consider an ideal gas contained in a vessel. if the intermolecular interaction suddenly beings to act, which of the following will happen?

(1) the pressure decreases

(2) the pressure increases

(3) the pressure remain unchanged

(4) the gas collapses

**Asked By: HIMANSHU MITTAL**

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**Joshi sir comment**

if the intermolecular interaction suddenly beings to act, then the pressure increases because due to intermolecular interaction gase will work as real gas

in the previous case if north pole is brought near the mettalic ring why the direction is reversed. we have to consider the drn of magnetic field of magnet or not. if yes then which drn N-S or S-N.

**Asked By: NIKHIL VARSHNEY**

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**Joshi sir comment**

The south pole of a magnet is bought near a metallic ring ,the direction induced current in the ring will be? Explain it clearly.

**Asked By: NIKHIL VARSHNEY**

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**Joshi sir comment**

If observer is in the side of magnet, then in the given case form **S** in the ring, it will give you clockwise direction

can you give me an idea of solving the parallel LC circuit? Also to find the phase difference between the I and E?

**Asked By: NIKHIL VARSHNEY**

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**Joshi sir comment**

1st make a 3 line circuit in which ac source, resistor with an inductor and resistor with a capacitor will be there in the three lines then divide total current "I"

from AC into the two legs, equations will be

**e = L di _{1}/dt + i_{1}R (1)**

**e =q _{2 }/ C + i_{2} R (2) here dq_{2} / dt = i_{2}**

now solve

_{ }

Why earth moves in orbital motion around the sun ...? why not in circular motion...?

**Asked By: HARISH**

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**Joshi sir comment**

Since every heavenly body like sun, earth, moon are rotating freely in free space, there is no body which is placed on a base, so rotation of every body depends on all the surrounding bodies. It means its track will also depend on the attraction forces given by all the surrounding bodies.

Two cylinders are twisted by the same external torque.If the ratios of their modulous of rigidity , radii & lengths are 1:2, 2:3 & 3:4 respectively. Then find the ratio of angle of twist ??

**Asked By: AMIT DAS**

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**Joshi sir comment**

Let the angle rotated due to torque = θ and angle of twist (shear) = δ

then arc covered = rθ (here r is radius)

now for twist of wire δ = rθ/l (here l is length)

according to formula η = F/Aδ and torque ζ = kFr (here k is constant of proportion)

we get ζ = kηAδr

Use the formula and get the answer, you have to calculate ratio of δ's so k is not required

how far from earth we can see earth as a whole elliptical?{we can clearly see the earth

**Asked By: SAHIL KUMAR**

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**Joshi sir comment**

for getting the complete vision we should draw tangents at the extreme of major and minor axis of the earth, this will give a point of intersection for which height from centre of earth will be R√2 so height from earth surface will be R√2 - R = R(√2-1)

here R is used for radius of earth

This is approximate calculation only

**Solution by Joshi sir**

for getting the complete vision we should draw tangents at the extreme of major and minor axis of the earth, this will give a point of intersection for which height from centre of earth will be R√2 so height from earth surface will be R√2 - R = R(√2-1)

here R is used for radius of earth