Video Solutions for GATE 1991 ECE : One Mark Questions ( Electron Devices )

1. A silicon sample is uniformly doped with 10¹⁶ phosphorous   

    atoms / cm³ and 2x 10¹⁶ boron atoms/cm³ . if all the dopants are 

    fully ionized, the material is 

              (a)  n-type with carrier concentration of 10¹⁶ /cm³

              (b)  p-type with carrier concentration of 10¹⁶ /cm³

              (c)  p-type with carrier concentration of 2x 10¹⁶ /cm³

      (d)  n-type with carrier concentration of 2x10¹⁶ /cm³

2. An n-type silicon sample, having electron mobility µ_n twice 

    the hole mobility µ_p, is subjected to a steady illumination such 

    that the electron concentration doubles from its thermal 

    equilibrium value. As a result, the conductivity of the sample 

    increases by a factor of……….

 Ans : 2

3. The small signal capacitance of an abrupt P⁺N junction is 

    1 nF/cm² at zero bias. If the built in voltage is 1 volt, the 

    capacitance at a reverse bias voltage of 99 volts is equal to …..

Ans :    0.1 nF /Cm2

4. Referring to the figure, the switch S is in position 1 initially and

    steady state conditions exist from time t=0  to t = t₀. The switch 

    is suddenly thrown into position 2. The current I flowing through

    the 10K resistor as function of time from t=0, is …………

    (Give the sketch showing the magnitudes of the current at t=0,  
      t=t₀ and t=∞)

 

5. Discrete transistors T1 and T2 having maximum collector

    current rating of 0.75 Amps are connected in parallel as shown

    in the figure. This combination is treated as a single transistor to 

    carry a total current of 1 Amp, when biased with self bias 

    circuit. When the circuit is switched on, T1 draws 0.55 Amps

    and T2 draws 0.45 Amps. If the supply is kept on continuously, 

    ultimately it is very likely that

             (a)   Both T1 and T2 get damaged

             (b)   Both T1 and T2 will be safe

             (c)   T1 will get damaged and T2 will be safe

             (d)   T2 will get damaged and T1 will be safe

6. The built in potential of the gate junction of an-channel JFET

    is 0.5 volts. The drain current saturates at V_DS = 4.0 volts 

    when V_GS = 0. The pinch off voltage is ______________

Ans :  - 4 volts

7. In figure, all transistors are identical and have a high value of 

    beta (β). The voltage V_DC is equal to _____

 

Ans :  5 volts

8. In figure the input V_i is a 100 Hz triangular wave having a 

    peak to peak amplitude of 2 volts and an average value of 

    zero volts. Given that the diode is ideal, the average value 

    of the output V_o is ______    Ans : 0.3 Volts

9. In figure, the n-channel MOSFETs are identical and their current 

    voltage characteristics are given by the following expressions:

 

Ans :  1 mA