Explanation:
In semiconductors at room temperature the electrons get enough energy so that they are able to over come the forbidden gap. Thus at room temperature the valence band is partially empty and conduction band is partially filled.
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A battery having e.m.f. 5V and internal resistance 0.5 W is connected with a resistance of 4.5 W then the voltage at the terminals of battery is
|
(a) 4.5 V |
(b) 4 V |
(c) 0 V |
(d) 2 V |
A gamma ray photon creates an electron- positron pair. If the rest mass energy of an electron is 0.5 MeV and the total K.E. of the electron- positron pair is 0.78 MeV, then the energy of the gamma ray photon must be
|
(a) 0.78 MeV |
(b) 1.78 MeV |
(c) 1.28 MeV |
(d) 0.28 MeV |
A heater coil is cut into two equal parts and only one part is now used in the heater. The heat generated will now be
|
(a) One fourth |
(b) Halved |
(c) Doubled |
(d) Four times |
Two particles X and Y having equal charges, after being accelerated through the same potential difference, enter a region of uniform magnetic field and describes circular path of radius 
and 
respectively. The ratio of mass of X to that of Y is
|
(a) |
(b) |
(c) |
(d) |
A magnet is suspended in such a way that it oscillates in the horizontal plane. It makes 20 oscillations per minute at a place where dip angle is 30o and 15 oscillations per minute at a place where dip angle is 60o. The ratio of total earth's magnetic field at the two places is
(a) 3
|
(b) 16 : 9
|
(c) 4 : 9 |
(d) 2
|
