Assertion (A): A backward wave oscillator can be used as a sweep generator. Reas

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Home Aptitude

Question
Assertion (A): A backward wave oscillator can be used as a sweep generator.
Reason (R): The frequency of oscillation of a backward wave oscillator can be changed by varying the voltage which controls the beam velocity.
Options
A. Both A and R are correct and R is correct explanation of A
B. Both A and R are correct but R is not correct explanation of A
C. A is correct but R is wrong
D. A is wrong but R is correct

Correct Answer

Both A and R are correct and R is correct explanation of A

Explanation

It is somewhat similar to TWT and can deliver microwave power over a wide frequency band.

It has an electron gun and a helix structure. However the interaction between electron beam and RF wave is different than in TWT.

The growing RF wave travels in opposite direction to the electron beam.

The frequency of wave can be changed by changing the voltage which controls the beam velocity.

Moreover the amplitude of oscillations can be decreased continuously to zero by changing the beam current.

It features are:

1. Frequency range - 1 GHz to 1000 GHz.

2. Power output - 10 mV to 150 mW (continuous wave) 250kW (pulsed).

It is used as signal source in transmitters and instruments.

2. In high frequency circuits impedance matching can be done by
1. open circuited stubs
2. short circuited stubs
3. transformer
Which of the above correct?
Options
A. 1, 2 and 3
B. 1 and 2 only
C. 1 and 3 only
D. 2 and 3 only

3. Assertion (A): Gate triggering is the most commonly used method for triggering of an SCR.
Reason (R): Even a small gate current is sufficient to turn on an SCR.
Options
A. Both A and R are correct and R is correct explanation of A
B. Both A and R correct but R is not correct explanation of A
C. A is correct but R is wrong
D. A is wrong but R is correct

6. Assertion (A): PIN diode is commonly used for microwave control.
Reason (R): A PIN diode uses heavily doped p and n materials.
Options
A. Both A and R are correct and R is correct explanation of A
B. Both A and R are correct but R is not correct explanation of A
C. A is correct but R is wrong
D. A is wrong but R is correct

7. Assertion (A): The velocity factor of a line is the ratio of wave velocity on the line to speed of light.
Reason (R): If the conductors of a line are immersed in a non magnetic insulating liquid, the wave velocity increases.
Options
A. Both A and R are correct and R is correct explanation of A
B. Both A and R are correct but R is not correct explanation of A
C. A is correct but R is wrong
D. A is wrong but R is correct

8. The magnitudes of OC and SC input impedances of a transmission line an 100 ? and 25 ?. The characteristic impedance is
Options
A. 25 ?
B. 50 ?
C. 75 ?
D. 100 ?

9. Assertion (A): A quarter wave transformer is used to match a resistive load to a transmission line.
Reason (R): A quarter wave transformer is a transmission line of quarter wave length.
Options
A. Both A and R are correct and R is correct explanation of A
B. Both A and R are correct but R is not correct explanation of A
C. A is correct but R is wrong
D. A is wrong but R is correct