Bharat Electronics Limited (BEL) Question Bank continued from Part 1…
Q-7. What is Balun?
A : Balun is a type of electrical transformer that is used to convert a balanced circuit (in which two signals are working against each other and ground is irrelevant) to a unbalanced circuit (in which a single signal is working against ground or pseudo-ground) hence the name balun.
Q-8. What is an isotropic antenna?
A : It is an antenna which radiates equal power in all directions. It is an ideal antenna and thus has no physical significance but is generally used as a reference antenna for other antennas.
Q-9. What is gain bandwidth product of a microwave transistor FT?
A : It is the frequency at which alpha (Ic / IE) of the transistor falls by 3 dB.
Q-10. What is transferred electron bulk effect? Name an element/compound in which it occurs.
A : It is defined as the change in the effective drift mobility of charge carriers in a semiconductor when a significant number of electrons are transferred from a low-mobility valley of the conduction band in a zone to a high-mobility valley or vice-versa and occurs in Gallium Arsenide (GaAs).
Q-11. What do you mean by negative resistance of a tunnel diode?
A : Tunnel diode is a device which exhibits the property of negative resistance in which current through the diode decreases on increasing the voltage across it.
Q-12. What is the value of free space impedance?
A : Free space impedance has an approximate value of 120π or 377Ω.
Q-13. How is telephone traffic measured?
A : Telephone traffic is generally measured with echo.
(Continued to Part 3…)