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Electronics Engineering Objective Questions { Semiconductor Physics and Diodes }

120. When a diode is forward biased
A. Barrier potential increases
B. Barrier potential decreases
C. Majority current reduces
D. Minority current reduces
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121. Thw work function of a photo surface whose threshold wave length is 12,000 A, will be
A. 0.103 eV
B. 0.673 eV
C. 1.03 eV
D. 1.27 eV
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122. A potential difference is developed across a current carrying metal strip when the strip is placed in a transverse magnetic field. the above effect is known as
A. Fermi's effect
B. Photo electric effect
C. Joule's effect
D. Hall's effect
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123. As the temperature of a semi-conductor is reduced to absolute zero
A. all electrons become free
B. all electrons cease to move
C. all valance electrons tend to remain in the valaence band
D. all valance electrons shift to forbidden gap
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124. The crystal structure of silicon is
A. Simple cubic
B. Body central cubic
C. Face centred cubic
D. Diamond
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125. For insulators the energy gap is of the order of
A. 0.1 eV
B. 0.7 eV
C. 1.1 to 1.2 eV
D. 5 to 15 eV
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126.  The photo electric threshold of tungsten is 2300 A. The energy of the electrons ejected from the surface by ultra-violet light of wavelength 1800 A, will be
A. 0.15 eV
B. 1.5 eV
C. 150 eV
D. 1.5 keV
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