156. A p-type semiconductor is :
1. A silicon crystal doped with arsenic impurity.
2. A silicon crystal doped with aluminium impurity.
3. A germanium crystal doped with boron impurity.
4. A germanium crystal doped with phosphorus impurity.
(a) a, c are correct
(b) a, d are correct
(c) b, c are correct
(d) b, d are correct
157. Certain substances lose their electrical resistance completely at finite low temperature. Such substances are called :
(a) Semiconductors
(b) A good insulator
(c) P-type semiconductor
(d) N-type semiconductor
158. An intrinsic semiconductor has :
(a) Zero resistance at 0˚C
(b) An infinite resistance at 0˚C
(c) A finite resistance which decreases with increases in temperature
(d) A finite resistance which increases with increases in temperature
159. The addition of pentavalent impurity to a semiconductor creates more :
(a) Free electrons
(b) Holes
(c) Positrons
(d) Free electrons and holes
160. Reverse bias on a junction diode :
(a) Lower the junction potential barrier
(b) Raises the junction potential barrier
(c) Greatly increases the minority carriers
(d) Greatly increases the majority carriers
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