Tuesday, 11 June 2013

Video Solutions for GATE 1992 ECE : One Mark Questions ( Electron Devices )

1. A semiconductor is irradiated with light such that carriers are

    uniformly generated throughout its volume. The semiconductor

    is n-type with ND = 1019 per cm3. If the excess electron 

    concentration in the steady state is ∆n = 1015 per cm3 and

    if τp = 10 µsec (minority carrier life time), the generation rate 

   due to irradiation is

Ans : (a)

2. A PN junction with a 100 Ω resistor, is forward biased so that a 

    current of 100 mA flows. If the voltage across this combination

    is instantaneously reversed to 10 volts at t = 0, the reverse 

    current that flows through the diode at t=0 is approximately 

    given by 

                    (a)   0 mA                              (b)   100 mA      
                    (c)   200 mA                          (d)    50 mA

Ans : (b)

3. An infrared LED is usually fabricated from 

                  (a)      Ge                              (b)        Si                   

                  (c)        GaAs                       (d)        Ga As P

Ans : (C)

4. In a transistor having finite β, the forward bias across the base 

    emitter junction is kept constant and the reverse bias across the 

    collector base junction is increased. Neglecting the leakage 

    across the collector base junction and the depletion region 

    generating current, the base current will ________. 

(increase / decrease / remain constant).

Ans : Decreases

5. An n-channel JFET has a pinch off voltage of VP = -5volts, 

    VDS(max) = 20 volts, and gm = 2 mA/V. the minimum 

    ON resistance is achieved in the JFET for 

Ans : (b)

6. The JFET in the circuit shown in figure has an IDSS = 10 mA 

    and VP = 5 volts. The value of the resistance RS for 

    a drain current IDS of 6.4 mA is ______________
   (select the nearest value)

Ans :  (a)

7. If the transistors in figure, have high values of β and 

    a VBE of 0.65 volt, the current I, flowing through 

    the 2 KΩ resistance will be ________________________

(a)   1 mA               (b)   2 mA            (c)   3 mA              (d)    4 mA           
Ans : (a)

8. The 6 volts zener diode shown in figure has zero zener resistance

    and a knee current of 5 mA. The minimum value of R so that

    the voltage across it does not fall below 6 volts is :

Ans : (b)

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