All India Engineering / Architecture Entrance Examination (AIEEE)
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AIEEE 2007 Physics
Q. 15. Charges are placed on the vertices of a square as shown. Let 
be the electric field and V the potential at the centre. If the charges on A and B are interchanged with those on D and C respectively, then
- remains unchanged, V changes
- Both and V change
- and V remain unchanged
- changes , V remain unchanged
Sol: In initial case, is along (1) whereas in final case is along (2). Potential at centre remains same.
Correct choice: (4)
Q. 16. The half-life period of a radio-active element X is same as the mean life time of another radio-active element Y. Initially they have the same number of atoms. Then
- X will decay faster than Y
- Y will decay faster than X
- X and Y have same decay rate initially
- X and Y decay at same rate always
Sol: 
, Y will decay faster than X
Correct choice: (2)
Q. 17. A Carnot engine, having an efficiency of 
as heat engine, is used as a refrigerator. If the work done on the system is 10 J, the amount of energy absorbed from the reservoir at lower temperature is
- 99 J
- 90 J
- 1 J
- 100 J
Sol: 
If same carnot engine is used as refrigerator then 
Correct choice: (2)