WBUT question of EM Theory

2004

1. (a) the unit of electrical flux density is

(b) A transmission line of length λ/4 shorted at far end behavers like

(c) Impedance inversion may be obtained with a

(d) A transmission line is terminated by a pure capacitor, the VSWR in the line is

(e) UHF radio wave propagate as

(f) The radiation resistance of an antenna is the

(g) The standard reference antenna for the directive gain is the

(h) The pointing vector gives the

(i) Which of the following layers persists at night?

(j) For satellite communication, the frequency, should be

2. (a) Wright the Maxwell’s equation for time varying electromagnetic field, when the medium is homogenous, source free, lossless, isotropic and linear. Explain the properties of the parameters of the medium.

(b) Electric field component of a propagating electromagnetic wave in free space are gives as

W_x=E_z=0 and E_y=E_ocos(wt-B_z)

Determine the field components of the magnetic field.

3. (a) Define and explain the line parameters of a transmission line. Indicate the units of these parameters.

(b) Derive the expression of input voltage and input current in term of output voltage and output current and the relative parameters of line.

4. (a) Explain what is meant by retarded vector potentials ? Derive the expression for far field components of electrical and magnetic fields due to a current element ID1.

(b) Explain the terms: Gain; Effective aperture; Radiation resistance of an antenna.

5. (a) Assuming flat earth, derive the expression of the electrical field received by a antenna from a transmitting antenna radiating a signal of P watt a UHF . Assuming also that the earth is a good conducer and height of the antenna (h₁ andh₂) are significantly less than their distanced.

(b) Wright a short note on duct propagation.

6. (A) derive the expression of input impedance Z in of a lossless transmission line in terms of relevant parameters, when the line is terminated in a load impedance Z_L .

(b) Give s neat sketch of variation of Z in as a function of the electric length of the line, when the line is terminated in a (a) short circuit and(b) open circuit, Discuss the significance of the plots .

7. (a) Explain the inconsistency present in the Ampere’s law. How the law is modified by Maxwell? Explain.

(b) Establish the expression of the frequency at which the conduction current equals to displacement current within an unbound medium. Find the frequency for a medium having σ=5.0 S/m and Є_r=1.