In a backward wave oscillator the wave travelling along the line winds itself ba

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Correct Answer

travelling along the line winds itself back and forth

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.

1. A 3 phase induction motor is controlled by voltage and frequency control such that the ratio V/f is constant. At 50 Hz, the speed is 1440 rpm. At 25 Hz, the speed is likely to be
Options
A. about 1350 rpm
B. about 720 rpm
C. about 360 rpm
D. either (b) or (c)

4. Assertion (A): A transistor has lower voltage drop during conduction as compared to thyristor
Reason (R): Transistors are manufactured in very high voltage and current ratings.
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

5. 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

7. For type 2 system, the magnitude and phase angle of the term (j?)² in the denominator, at ? = 0, are respectively
Options
A. 0 and - 90�
B. 0 and + 90�
C. infinity and - 180�
D. infinity and + 180�