Solve your IGNOU Doubts

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.

See Answer →

Question:

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

See Answer →

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.

See Answer →

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.

See Answer →

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

See Answer →

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.

See Answer →

Question:

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

See Answer →

Question:

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

See Answer →

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.

See Answer →

Question:

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

See Answer →

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.

See Answer →

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.

See Answer →

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?

See Answer →

Question:

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

See Answer →

Question:

How do we differentiate between diamagnetic and paramagnetic materials? Show that for diamagnetic atoms placed in an external magnetic field $B$ , the change in dipole moment is opposite to the direction of $B$

See Answer →

Question:

A 10 eV electron is circulating in a plane at right angles to a uniform magnetic field of $1.0\times10^{4}$ T. Calculate the orbital radius of the electron, cyclotron frequency, period of revolution, and the direction of circular motion of the electron as viewed by an observer looking along the magnetic field.

See Answer →

Question:

A copper wire of diameter 2 mm and length 30 m is connected across a battery of 2V. Calculate the current density in the wire and drift velocity of the electrons. The resistivity of copper is $1.72\times 10^{-8}\,\Omega m\, and\,n=8.0\times10^{28}$ electrons $m^{-3}.$ .

See Answer →

Question:

A glass of relative permittivity 5 is kept in an external electric field of magnitude $10^2\,Vm^{-1}$ . Calculate the polarisation vector, molecular/atomic polarisability and the refractive index of the glass.

See Answer →

Question:

The capacitance of a parallel plate capacitor is increased by a factor of 6 when a dielectric material fills the space between its plates. What is the relative permitivity of the dielectric material? If this material is placed in between the plates of a cylindrical capacitor of outer and inner radii 12 cm and 10 cm respectively, calculate the capacitance per unit length of the cylindrical capacitor.

See Answer →

Question:

Consider the figure given below. Charges $q_1,q_2$ and $q_3$ are placed at $P,Q$ and R, respectively, and $q_1=q_2=-q_3=2\mu C.$ Determine the magnitude and the direction of the electric field at point A.