Solve your IGNOU Doubts

Question:

The mean speed of oxygen molecules is 450 $ms^{-1}.$

If the radius of an oxygen molecule is 1.8 Å, calculate mean time between two successive collisions and mean free path. Take $n=3\times 10^{25}m^{-3}.$

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Question:

c) A Carnot engine has an efficiency of 40%. Its efficiency is to be raised to 50%. By how much must the temperature of the source be increased if the sink is a $27$ $\,^{\circ}C$ .

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Question:

b) Define adiabatic lapse rate? Obtain an expression for adiabatic lapse rate for earth’s atmosphere?

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Question:

a) A block of metal whose volume expansivity is $5.0\times 10^{-5}\,^{\circ}C^{-5}$ and isothermal compressibility is $1.2\times 10^{-6}$ $atm^{-1}$ has volume 5 litre at 1 atm and $20$ $\,^{\circ}C$ . On applying pressure, its temperature rises by

applying pressure, its temperature rises by $10$ $\,^{\circ}C$ and volume increases by 0.5 $cm^3.$ Calculate the pressure applied.

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Question:

The refractive indices of the core and cladding materials of an optical fibre are 1.51 and 1.39 respectively. Calculate the numerical aperture and light gathering capacity of the fibre.

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Question:

Two energy levels of an atomic system are separated by energy corresponding to frequency $3.0\times10^{14}$ Hz. Assuming that all atoms are in one or the other of these two energy levels, compute the fraction of atoms in the upper energy level at temperature 400 K. Take $k_B=1.38\times10^{23}JK^{34}$ and $h=6.6\times 10^{-34}$ Js

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Question:

An atomic system consisting of two energy levels, with population of higher energy level less than that of the lower level, is in thermal equilibrium. Show that the absorption of radiation dominates stimulated emission if radiation of appropriate frequency is introduced into the system. Comment on the consequences of this fact for laser action.

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Question:

Discuss Rayleigh’s criterion for resolving power of an optical instrument. Obtain an expression for resolving power of a microscope.

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Question:

A plano-convex lens of radius 1.0 m is placed on an optically flat glass plate and is illuminated by an extended monochromatic source. Assume that the point of contact is perfect. The diameters of the 10th and 5th dark rings in the reflected light are $4.50\times10^{-3}m$ and $3.36\times10^{-3}.$ Next, the space between the lens and the glass plate is filled with a liquid. The diameter of the 5th ring changes to $3.0\times10^{-3}m.$ Calculate the refractive index of the liquid when the ring is (i) dark, and (ii) bright, if the wavelength of light is 589 nm.

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Question:

Obtain the expression for shift in fringes when a thin transparent sheet is introduced in the path of one of the waves in a double slit interference experiment.

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Question:

Obtain an expression for elliptically polarised light resulting due to superposition of two orthogonal linearly polarised light waves. Show that plane polarised light and circularly polarised light are special cases of elliptically polarised light

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Question:

Obtain expressions for reflection and transmission amplitude coefficients when electric vector associated with a plane monochromatic electromagnetic wave is in the plane of incidence.

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Question:

Discuss the concept of missing orders with reference to double slit diffraction pattern.

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Question:

Discuss the concept of missing orders with reference to double slit diffraction pattern.

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Question:

The sodium lamp used in a physics laboratory gives out light uniformly. Suppose that the lamp uses 60 W. Calculate the magnitude of electric field.

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Question:

Describe polarisation of light by reflection. How does degree of polarisation vary with angle of incidence of light?

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Question:

A sinusoidal plane electromagnetic wave propagates from water $(n_w=1.33)$ to glass $(n_w=1.5).$ Calculate the reflection and transmission coefficients for this wave at the interface of the two media. Show that when an electromagnetic wave enters from one dielectric medium to the other, its frequency remains unchanged.

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Question:

Explain the physical significance of the Maxwell’s equation $\bigtriangledown \times B=\mu_0 \left ( J+\varepsilon _0\frac{\partial E}{\partial t} \right ).$

Derive the wave equation for the z-component of the electric field of an electromagnetic wave.

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Question:

An electric generator comprises a square wire loop of side 80 cm. The loop has 50 turns and is placed in a magnetic field of 0.5 T. By what frequency should this loop be rotated in the magnetic field to produce an AC voltage of peak value 250 V?

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Question:

Establish the relation $B$ $=\mu _0(H+M)$ for a ferromagnetic material.