All India Engineering / Architecture Entrance Examination (AIEEE)
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AIEEE 2007 Physics
Q. 18. Carbon, silicon and germanium have four valence electrons each. At room temperature which one of the following statements is most appropriate?
- the number of free conduction electrons is significant in C but small in Si and Ge.
- the number of free conduction electrons is negligibly small in all the three.
- the number of free electrons for conduction is significant in all the three.
- the number of free electrons for conduction is significant only in Si and Ge but small in C.
Sol: Correct choice: (4)
Q. 19. A charged particle with charge q enters a region of constant, uniform and mutually orthogonal fields 
and 
with a velocity 
perpendicular to both and , and comes out without any change in magnitude or direction of .
Sol: 
Magnitude of 
and direction of should be such that net force on charge particle be zero. should be in the direction perpendicular to plane of and and coming out of plane. So direction of is in the direction of 
Correct choice: (1)
Q. 20. The potential at a point x (measured in 
) due to some charges situated on the x-axis is given by 
. The electric field is 
given by
- 5/3
and in the –ve x direction - 5/3 and in the +ve x direction
- 10/9 and in the –ve x direction
- 10/9 and in the +ve x direction
Sol: 
Correct choice: (4)