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Home Electronics and Communication Engineering Microwave Communication See What Others Are Saying!
  • Question
  • The external magnetic field in a magnetron is such that lines are


  • Options
  • A. parallel to the axis of cathode
  • B. perpendicular to the axis of cathode
  • C. inclined to the axis of cathode
  • D. either (b) or (c)

  • Correct Answer
  • parallel to the axis of cathode 

    Explanation
    The operation of magnetron is based on interaction of electromagnetic fields with electrons moving in static electric and magnetic fields oriented at 90° with respect to each other.

    In a magnetron three forces act on electron viz. force due to electric field (equal to - eE), force due to magnetic field [equal to - e (v x B)] and centrifugal force (equal to mv2/r).

    The path of the electron can be found by balancing these three forces. Magnetron can be of three types i.e., negative resistance device, cyclotron frequency device and travelling wave or cavity device.

    In negative resistance magnetron use is made of the negative resistance between two anode segments.

    It has low efficiency and is used at frequencies less than 0.5 GHz.

    In cyclotron magnetron a synchronism exists between ac component of electric field and periodic oscillation of electrons in a direction parallel to the field.

    It is used for frequencies higher than 100 MHz.

    A cavity magnetron has a number of cylindrical cavities in the interaction region.

    The cavity magnetron is the most common type of magnetron. Its features are :

    1. Frequency range - 500 MHz to 10 GHz

    2. Power output - 250 kW (pulses)

    3. Efficiency - about 50%

    It is used in radar systems, industrial heating systems and microwave ovens.


    More questions

    • 1. Schrodinger wave equation is partial differential equation.

    • Options
    • A. True
    • B. False
    • Discuss
    • 2. The output frequency of a cycloconverter can be changed by changing the firing angle.

    • Options
    • A. True
    • B. False
    • Discuss
    • 3. Most of the memory chips in static RAM

    • Options
    • A. do not require any supply
    • B. need 2 V supply
    • C. need 5 V supply
    • D. need 12 V supply
    • Discuss
    • 4. In crystalline solids, atoms are stacked in a regular manner.

    • Options
    • A. True
    • B. False
    • Discuss
    • 5. The classes of solid dielectrics are

    • Options
    • A. A, B, C, D, E, F, H
    • B. A E B F H C D
    • C. Y A E B F H C
    • D. A E B F H C
    • Discuss
    • 6. The unit for mmf is

    • Options
    • A. A
    • B. Wb
    • C. T
    • D. V
    • Discuss
    • 7. In a single phase full wave regulator, the firing angles in the positive and negative half cycles are generally

    • Options
    • A. equal
    • B. different
    • C. equal or different
    • D. different but sometimes equal
    • Discuss
    • 8. The real part of complex dielectric constant and tan? for a dielectric are 2.1 and 5 x 10-4 at 100 Hz respectively. The imaginary part of dielectric constant at 100 Hz is

    • Options
    • A. 1.05 x 10-3
    • B. 2.1 x 10-3
    • C. 5 x 10-3
    • D. 1.05 x 10-2
    • Discuss
    • 9. The units for ?r are

    • Options
    • A. Farads
    • B. Farads/m
    • C.
    • D. no units
    • Discuss
    • 10. Tesla is a unit of

    • Options
    • A. flux
    • B. field strength
    • C. flux density
    • D. MMF
    • Discuss


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