Physics - Electronic Devices

Question - 1

For a germanium sample, traces of gallium are added as an impurity. The resultant sample could behave like

  • A a conductor
  • B an n-type semiconductor
  • C a p-type semiconductor
  • D an insulator

Question - 2

The conductivity of a semiconductor increases with increase in temperature, because

  • A number density of free current carriers increases
  • B relaxation time increases
  • C both number density of carriers and relaxation time increase
  • D number density of current carriers increases, relaxation time decreases but effect of decrease relaxation time is much less than increase in number density.

Question - 3

For pure Ge semiconductor, quantity of electron and hole is 1019 e/m3 . If we doped a donor impurity in it with density 1023 e/m3, then quantity of hole (e/m3) in a semiconductor is

  • A 1015
  • B 1019
  • C 1023
  • D 1027

Question - 4

Mobility of electrons in n-type Ge is 5000 cm2 /V-s and conductivity is 5 mho/cm. If the effect of holes is negligible, then impurity concentration will be

  • A 6.25 x 1015/cm3
  • B 9.25 x 1014/cm3
  • C 6 x 1013/cm3
  • D 9 x 1013/cm3

Question - 5

In sample of pure silicon 1023 e/m3  is mixed to phosphorous. If all atoms are active, then what will be the resistivity at 20oC, if mobility of electron is 1200 cm2/V-s?

  • A 0.5209 ohm-cm
  • B 5.209 ohm-cm
  • C 52.09 ohm-cm
  • D 520.9 ohm-cm

Question - 6

What will be conductivity of pure silicon crystal at 300 K temperature, if electron-hole pairs per cm3 are 1.072 x 1010, \(\mu_e\) = 1350 cm2/V-s and  \(\mu_e\) = 480 cm2/V-s ?

  • A 3.14 x 10-6 mho/cm
  • B 3 x 106 mho/cm
  • C 10-6 mho/cm
  • D 106 mho/cm

Question - 7

Forbidden energy gap of Ge is 0.75 eV. Maximum wavelength of incident radiation of photon for producing electron-hole pair in germanium semiconductor is

  • A 4200 Å
  • B 16500 Å
  • C 4700 Å
  • D 4000 Å

Question - 8

In which case, the junction diode is not reverse biased?

  • A
  • B
  • C
  • D

Question - 9

Ripple factor of half-wave rectifier is

  • A 1.21
  • B 1.6
  • C 1.5
  • D 1.4

Question - 10

In an n-p-n transistor circuit, the collector current is 10 mA. If 90% of the electrons emitted, reach the collector, the emitter current(IE) and base current (IB) are given by.

  • A IE = 1 mA; IB=11 mA
  • B IE = 11 mA; IB=1 mA
  • C IE = -1 mA; IB=9 mA
  • D IE = 9 mA; IB=-1 mA
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