- AHOMO
- BValence band
- CConduction band
- DLUMO
Explanation:
The band gap in case of semiconductors is of order 3−4 eV. At absolute zero, the valence band is filled and conduction band is empty, so it behaves as an insulator. As the temperature is raised, electrons in the valence band gain sufficient energy to overcome the band gap and jump to the conduction band.
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Solid targets of different elements are bombarded by highly energetic electron beams. The frequency (f) of the characteristic X-rays emitted from different targets varies with atomic number Z as
|
(a) f ∝ |
(b) f ∝ |
(c) f ∝ Z |
(d) f ∝ |
If n, e, τ and m respectively represent the density, charge relaxation time and mass of the electron, then the resistance of a wire of length l and area of cross-section A will be
|
(a) |
(b) |
(c) |
(d) |
The work function of a metallic surface is 5.01 eV. The photo-electrons are emitted when light of wavelength 2000Å falls on it. The potential difference applied to stop the fastest photo-electrons is [h = 4.14 ![]()
|
(a) 1.2 volts |
(b) 2.24 volts |
(c) 3.6 volts |
(d) 4.8 volts |
If be the electric field strength of a short dipole at a point on its axial line and
that on the equatorial line at the same distance, then
|
(a) |
(b) |
(c) |
(d) None of the above |
Refractive index of air is 1.0003. The correct thickness of air column which will have one more wavelength of yellow light (6000 Å) than in the same thickness in vacuum is
|
(a) 2 mm |
(b) 2 cm |
(c) 2 m |
(d) 2 km |