For the sustained interference of light, the necessary condition is that the two sources should
|
(a) Have constant phase difference |
(b) Be narrow |
|
(c) Be close to each other |
(d) Of same amplitude |
(a) Have constant phase difference
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and 
represents gravitational and electrostatic force respectively between electrons situated at a distance 10 cm. The ratio of 
is of the order of
|
(a) |
(b) 10 |
(c) 1 |
(d) |
X-rays are not used for radar purpose because
| (a) They are not reflected by the target |
| (b) They are not electromagnetic waves |
| (c) They are completely absorbed by the air |
| (d) They sometimes damage the target |
Liquid oxygen remains suspended between two pole faces of a magnet because it is
|
(a) Diamagnetic |
(b) Paramagnetic |
(c) Ferromagnetic |
(d) Antiferromagnetic |
Assertion : At a point in space, the electric field points towards north. In the region, surrounding this point the rate of change of potential will be zero along the east and west.
Reason : Electric field due to a charge is the space around the charge.
|
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion. |
|
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion. |
|
(c) If assertion is true but reason is false. |
|
(d) If the assertion and reason both are false. |
The activity of a radioactive sample is measured as 9750 counts per minute at t = 0 and as 975 counts per minute at t = 5 minutes. The decay constant is approximately
|
(a) 0.230 per minute |
(b) 0.461 per minute |
|
(c) 0.691 per minute |
(d) 0.922 per minute |
