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.

EXAM of WBUT

The even semester exam is going to started . the exam is started in the first week of June from 10.

students are start their preparation for examination . so in point of view of importance exam here i am posting the previous years question .this is help full for all 2nd year student .i am to do hard work for writing the question because we know the question of WBUT are not present on the internet .
Firstly i post the question paper of EM theory of 2006 and 2005 ,which give the basic idea of question paper and impotent question .

so enjoy the exam.

WBUT question of EM theory 2005

2005

1. Define the following terms connected with sky wave propagation: Virtual height, critical frequency, skip distance and Fading.

2. Write the definition of (i) Isotropic antenna, (ii) Beam width. Show that the directive of an elemental antenna is 1.5.

3. Explain the effect of ground on the propagation characteristics of radio wave in the medium and shout wave bands.

4. Why did Maxwell introduce the concept of displacement current? Explain how the vector potential equation was subsequently modified by this concept.

5. What is meant by Magnetic vector potential? How is circularly polarized EM-wave produced?

6. Given E=A_y[10cos(10⁶t-B_y)], at a point in air ,find H and the pointing vector at that point.

7. State Faraday’s laws of electromagnetic induction and express the same in differential form as used in Maxwell’s electromagnetic field equation.

8. Starting form Maxwell’s field equation in their differential form, prove that the pointing vector gives the power flow per unit area of cross section, at a point in the medium of propagation.

9. Calculate the amplitudes of the reflected and refracted waves in terms of the incident wave amplitude assuming plane monochromatic waves incident normally on the boundary surface between two dielectrics.

10. Starting from the expressions of electrical and magnetic fields due to a short dipole, derive an expression of its radiation resistance.

11. Derive the expression for radiation resistance of elemental dipole antenna.

12. Starting with Maxwell’s equation derive the equation.

∆²E=ЄH∂²E/∂²t +ЄH∂²E/∂²t

For a linear, homogeneous isotropic medium characterized by Є, σ and μ where the symbols have their usual meaning.

13. Show that the ratio of the electrical magnetic magnetic field of a uniform plane wave is a constant depending upon the medium and that the electrical and magnetic fields are perpendicular to each other.

14. A long cylinder of radius a and length L carries a uniform magnetization M parallel to its axis .the cylindrical magnet passes at constant velocity V through a circular ring of slightly larger diameter. Graph the emf induced in the ring as a function of time giving reason thereof.

15. Explain what are meant by

(i) Surface wave

(ii) Ground wave

WBUT question of EM theory of 4th sem

2006
Group-B
2(a). What do you mean by self inductance?
(B). A 3 cm long solenoid carries a current of 400mA. IF the solenoid is to produce a magnetic flux density of 5 mWb/m², how many turns of wire are needed?
3 (a) State Ampere's circuit law.
(b) A hollow conducting cylinder has inner radius a and outer radius b and carries current I along the positive Z-direction .Find H everywhere.
4(a) States Faraday's law. From the fundamental principle establish the relation

∆×B= -∂B/∂t

5. What do u you mean by effective height of an antenna? Calculate it for linear and sinusoidal distribution of current.

6. what do you mean by skin effect? Calculate the skin depth for radio waves of wavelength 3 m (in free space) in copper, the electrical conductivity of which is 6×10⁷ s/m.

Group C

7(a) Write the maxwell’s equation for time varying electromagnetic fields, when the medium is homogeneous, source free, loss less, isotropic and linear. Explain the properties of the parameters of the medium.

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

8(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 load impedance, Z_L.

(b) Give a neat sketch of variation of Z_in as a function of electrical length of the line, when the line is terminated in a (i) short circuit and (ii) open circuit. Discuss the significance of the plots.

9(a) Explain the mechanism for tropospheric scatter propagation.

(b) What is radio horizon?

(c) Derive the expression for critical frequency for sky wave propagation.

10(a) Explain the formation of standing wave pattern on transmission line.

(b) Deduce the relation between the reflection co-efficient and VSWR.

(c) A 70Ω lossless line has S=1.6 an θ_k=300⁰. If the line is 0.6λ long, obtain

(i) K, Z_{L, ,} Z_in (ii) the distance of the first minimum voltage fro

11 Find the relationship between the effective aperature and directivity of an antenna. Show that the effective aperture for isotropic antenna is 0.079 λ². Derive an expression for the Friis formula in communication system.

m the load.