The valence band and conduction band of a solid overlap at low temperature, the solid may be
|
(a) A metal |
(b) A semiconductor |
(c) An insulator |
(d) None of these |
(a) A metal
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In Bohr model of hydrogen atom, the ratio of periods of revolution of an electron in n = 2 and n = 1 orbits is
|
(a) 2 : 1 |
(b) 4 : 1 |
(c) 8 : 1 |
(d) 16 : 1 |
Our eye is most sensitive for which of the following wavelength
|
(a) 4500 Å |
|
(b) 5500 Å |
|
(c) 6500 Å |
|
(d) Equally sensitive for all wave lengths of visible spectrum |
The resistance of a 5 cm long wire is 10 W. It is uniformly stretched so that its length becomes 20 cm. The resistance of the wire is
|
(a) 160 W |
(b) 80 W |
(c) 40 W |
(d) 20 W |
A star is moving away from the earth with a velocity of 100 km/s. If the velocity of light is 3 
then the shift of its spectral line of wavelength 5700 Å due to Doppler's effect will be
|
(a) 0.63 Å |
(b) 1.90 Å |
(c) 3.80 Å |
(d) 5.70 Å |
Two conducting spheres of radii 5 cm and 10 cm are given a charge of 15 μC each. After the two spheres are joined by a conducting wire, the charge on the smaller sphere is
|
(a) 5 μC |
(b) 10 μC |
(c) 15 μC |
(d) 20 μC |
In an insulator, the forbidden energy gap between the valence band and conduction band is of the order of
| (a) 1 MeV | (b) 0.1 MeV |
(c) 1eV |
(d) 5 eV |