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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. If an amplifier with gain of - 1000 and feedback factor ? = - 0.1 had a gain change of 20% due to temperature, the change in gain of the feedback amplifier would be

    • Options
    • A. 10%
    • B. 5%
    • C. 0.2%
    • D. 0.01%
    • Discuss
    • 2. Permeability is analogous to

    • Options
    • A. resistivity
    • B. retentivity
    • C. conductivity
    • D. coercivity
    • Discuss
    • 3. In a Gunn diode oscillator drift velocity of electron is 107 cm/s and active region length is 10 x 10-4 cm. The natural frequency of oscillation is

    • Options
    • A. 1 MHz
    • B. 10 MHz
    • C. 1 GHz
    • D. 10 GHz
    • Discuss
    • 4. A cycloconverter is a group of controlled rectifiers.

    • Options
    • A. True
    • B. False
    • Discuss
    • 5. If the valence electron is separated from a copper atom, the remaining part of atom has a net charge of

    • Options
    • A. 1
    • B. - 1
    • C. 0
    • D. + 3
    • Discuss
    • 6. A single phase bridge type cycloconverter uses eight thyristors.

    • Options
    • A. True
    • B. False
    • Discuss
    • 7. ?r is determined by the atomic structure of the dielectric.

    • Options
    • A. True
    • B. False
    • Discuss
    • 8. An SBS can conduct is one direction only.

    • Options
    • A. True
    • B. False
    • Discuss
    • 9. The resistivity of intrinsic semiconductors, at room temperature, is of the order of

    • Options
    • A. 1 ?-m
    • B. 1000 ?-m
    • C. 106 ?-m
    • D. 10-3 ?-m
    • Discuss
    • 10. The orientation polarization of a polyatomic gas is inversely proportional to absolute temperature.

    • Options
    • A. True
    • B. False
    • Discuss


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