### GATE 1987 Video Solutions on EDC (Electronic Devices and Circuits)

1.       Consider two energy levels : E1, E eV above the Fermi level and E2, E eV below the Fermi level. P1 and P2 are the probabilities of E1 and E2 being occupied by the electron respectively. Then
a.       P1 > P2
b.      P1 = P2
c.       P1 < P2
d.      P1 and P2 depend on number of free electrons

2.       In an intrinsic semiconductor, the free electron concentration depends on
a.       Effective  mass of electrons only
b.      Effective mass of holes only
c.       Temperature of the semiconductor
d.      Width of the forbidden energy band of the semiconductor

3.       According to the Einstein relation, for any semiconductor, the ratio of diffusion constant to mobility of carriers
a.       Depends upon the temperature of the semiconductor
b.      Depends upon the type of the semiconductor
c.       Varies with life time of the semiconductor
d.      Is a universal constant

4.       Direct band gap semiconductors
a.       Exhibit short carrier lifetime and they are used for fabricating BJTs
b.      Exhibit long carrier lifetime and they are used for fabricating BJTs
c.       Exhibit short carrier lifetime and they are used for fabricating LASERs
d.      Exhibit long carrier lifetime and they are used for fabricating LASERs

5.       The diffusion capacitance of a PN junction
a.       Decreases with increasing current and increasing temperature
b.      Decreases with decreasing current and increasing temperature
c.       Increases with increasing current and increasing temperature
d.      Does not depend on current and temperature

6.       The pinch off voltage for an n-channel JFET is 4 volts, then pinch off occurs for VDS when VGS = -1 volts is
a.       3 volts
b.      5 volts
c.       4 volts
d.      1 volts