36. For a quarter wave transformer characteristic impedance is related with input and load impedance—

1. 1. Z₀ = √Z_R/Z_S

   
   
   

   2. Z₀ = √Z_R.R_S

   
   
   

   3. Z0 =	√	ZR
      		Zs

   
   
   

   4. Z0 =	1
      	√ZsZS

   
   
   

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   Refer synopsis

   Correct Option: B

   Refer synopsis

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37. Choose the correct statements:
    For a wave propagating in an air filled rectangular waveguide—

1. 1. Waveguide wavelength is never less than the free space wavelength.

   
   
   

   2. Wave impedance is never less than the free space impedance.

   
   
   

   3. Phase velocity is never less than the free space velocity.

   
   
   

   4. TEM mode is possible if the dimensions of the waveguide are properly chosen.

   
   
   

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   Refer synopsis

   Correct Option: C

   Refer synopsis

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38. The depth of velocity modulation in a two cavity Klystron amplifier can be increased by increasing the—

1. 1. Amplitude of the applied signal voltage

   
   
   

   2. Beam coupling coefficient

   
   
   

   3. Cavity gap transit angle

   
   
   

   4. Catcher d.c. voltage

   
   
   

   5. Both A and B

   
   
   

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   Depth of velocity modulation could be increased by	βiV1	where βi and V1 are coupling coefficient and amplitude of applied signal voltage
   	2V0

   Correct Option: E

   Depth of velocity modulation could be increased by	βiV1	where βi and V1 are coupling coefficient and amplitude of applied signal voltage
   	2V0

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39. Radiation resistance of a current element of length dl is—

1. 1. 80		λdl		2	ohms
      		λ

   
   
   

   2. 80λ		dl		2	ohms
      		λ

   
   
   

   3. 80		λdl		2	ohms
      		λ

   
   
   

   4. 80		λ	dl		2	ohms
      		2	λ

   
   
   

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   NA

   Correct Option: B

   NA

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40. Rectangular waveguide is designed to propagate the dominant mode TE₁₀ at a frequency of 5 MHz. The cutoff frequency is 0.8 of signal frequency the raito of the waveguide height to width is 2 the dimension of the waveguide are—

1. 1. 3.75 cm, 1.875 cm

   
   
   

   2. 4 cm, 2 cm

   
   
   

   3. 8 cm, 4 cm

   
   
   

   4. 2.54 cm, 1.27 cm

   
   
   

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   We find the relation of waveguide that the cut-off frequency is given by relation
   

   fc =

   1

   √

   m∏

   2

   +

   n∏

   2

   2∏√με

   a

   a

   
   

   for TE10 mode m = 1 and n = 0 and b =	1
   	a

   
   

   fc × 2∏	=	∏	⇒ a = 3.75 cm
   c		a

   
   and

   b =	a	= 1.875 cm
   	2

   Correct Option: A

   We find the relation of waveguide that the cut-off frequency is given by relation
   

   fc =

   1

   √

   m∏

   2

   +

   n∏

   2

   2∏√με

   a

   a

   
   

   for TE10 mode m = 1 and n = 0 and b =	1
   	a

   
   

   fc × 2∏	=	∏	⇒ a = 3.75 cm
   c		a

   
   and

   b =	a	= 1.875 cm
   	2

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