- A30K
- B40K
- C50K
- D60K
Explanation:
Bell laboratory has developed superconductor at a temperature of 40 K.Superconductivity is a phenomenon of exactly zero electrical resistance and expulsion of magnetic flux fields occurring in certain materials, called superconductors, when cooled below a characteristic critical temperature. It was discovered by Dutch physicist Heike Kamerlingh Onnes on April 8, 1911, in Leiden.
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A convex lens of focal length 40 cm is in contact with a concave lens of focal length 25 cm. The power of combination is
|
(a) – 1.5 D |
(b) – 6.5 D |
(c) + 6.5 D |
(d) + 6.67 D |
Plane polarised light is passed through a polaroid. On viewing through the polaroid we find that when the polariod is given one complete rotation about the direction of the light, one of the following is observed
|
(a) The intensity of light gradually decreases to zero and remains at zero |
|
(b) The intensity of light gradually increases to a maximum and remains at maximum |
|
(c) There is no change in intensity |
|
(d) The intensity of light is twice maximum and twice zero |
In Young’s double-slit experiment, an interference pattern is obtained on a screen by a light of wavelength 6000 Å, coming from the coherent sources S1 and S2. At certain point P on the screen third dark fringe is formed. Then the path difference S1P – S2P in microns is
|
(a) 0.75 |
(b) 1.5 |
(c) 3.0 |
(d) 4.5 |
A uniform wire of resistance R is uniformly compressed along its length, until its radius becomes n times the original radius. Now resistance of the wire becomes
|
(a) |
(b) |
(c) |
(d) nR |
In charging a battery of motor-car, the following effect of electric current is used
|
(a) Magnetic |
(b) Heating |
(c) Chemical |
(d) Induction |
A man with defective eyes cannot see distinctly object at the distance more than 60 cm from his eyes. The power of the lens to be used will be
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(a) + 60 D |
(b) – 60 D |
(c) – 1.66 D |
(d) |