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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. Consider a 300 ?, quarter wave long at 1 GHz transmission line as shown in figure. It is connected to a 10 V, 50 ? source at one end is left open circuited at the other end. The magnitude of the voltage at the open circuit end of the line is

    • Options
    • A. 10 V
    • B. 5 V
    • C. 60 V
    • D. 60/7 volt
    • Discuss
    • 2. The image frequency of a superheterodyne receiver is

    • Options
    • A. independent of the frequency at which the receiver is tuned
    • B. always outside the operating range of the receiver
    • C. typical to FM receivers only
    • D. not rejected by the IF tuned circuits
    • Discuss
    • 3. If a metal specimen has n valence electrons per m3 each having charge e and mass m and t is the relaxations time, the conductivity is

    • Options
    • A.
    • B.
    • C.
    • D.
    • Discuss
    • 4. The v-i characteristic shown in the given figure is for

    • Options
    • A. thermistor
    • B. photoconductor
    • C. varistor
    • D. none of the above
    • Discuss
    • 5. Fleming's left hand rule is used to find

    • Options
    • A. direction of force on a current carrying conductor
    • B. direction of flux in solenoid
    • C. direction of magnetic field due to a current carrying conductor
    • D. direction of induced emf
    • Discuss
    • 6. Consider the following materials

      1. Nickel
      2. Silver
      3. Oxygen
      4. Aluminium
      The correct sequence in the order of decreasing permeability is

    • Options
    • A. 1, 4, 3, 2
    • B. 1, 4, 2, 3
    • C. 4, 1, 3, 2
    • D. 4, 1, 2, 3
    • Discuss
    • 7. In a full bridge inverter, the waveshape of load current depends on

    • Options
    • A. relative values of load parameters R, L and C
    • B. relative values of load parameters R and L
    • C. relative values of load parameters L and C
    • D. gating frequency
    • Discuss
    • 8. In the basic series inverter circuit, the source supplies load

    • Options
    • A. only in positive half cycle
    • B. both in positive and negative half cycles
    • C. only in part of positive half cycle
    • D. in positive half cycle and part of negative half cycle
    • Discuss
    • 9. In rectifier circuits, ripple factor RF and form factor FF are related as

    • Options
    • A. RF = (FF2 - 1)0.5
    • B. RF = FF
    • C. RF = FF - 1
    • D. RF = (FF - 1)0.5
    • Discuss
    • 10. In a radio receiver

    • Options
    • A. the local oscillator frequency is made higher than the incoming signal frequency
    • B. the local oscillator frequency is made lower than the incoming signal frequency
    • C. the local oscillator frequency is made equal to the incoming signal frequency
    • Discuss


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