A prism of refractive index √2 has a refracting angle of 60°. At what angle a ray must be incident on it so that it suffers a minimum deviation?
45°
60°
90°
180°
A transparent cube of 15 cm edge contains a small air bubble. Its apparent depth, when viewed through one face, is 6 cm and when viewed through the opposite face is 4 cm. Then the refractive index of the material of the cube is:
2.0
2.5
1.6
1.5
The radius of the convex surface of the plano-convex lens is 20 cm and the refractive index of the material of the lens is 1.5. The focal length is :
30 cm
50 cm
20 cm
40 cm
If the work function of a metal is 4.2 eV, the cut-off wavelength is :
8000 Å
7000 Å
1472 Å
2950 Å
Regarding a semiconductor which one of the following is wrong?
There are no free electrons at room temperature
There are no free electrons at 0K
The number of free electrons increases with the rise of temperature
The charge carriers are electrons and holes
Nuclear fusion is common to the pairs :
thermonuclear reactor, uranium based nuclear reactor
energy production in sun, uranium-based nuclear reactor
energy production in sun, hydrogen bomb
the disintegration of heavy nuclei, hydrogen bomb
Which of the following statements is true for an n-type semi-conductor?
The donor level lies closely below the bottom of the conduction band
The donor level lies closely above the top of the valence band
The donor level lies at the halfway mark of the forbidden energy gap
None of the above
The refractive index of the material of the prism and liquid are 1.56 and 1.32 respectively. What will be the value of θ for the following refraction?
A person who can see things most clearly at a distance of 10 cm, requires spectacles to enable to see clearly things at a distance of 30 cm. What should be the focal length of the spectacles?
15 cm (concave)
15 cm (convex)
10 cm (concave)
0
A.
15 cm (concave)
Since the person is not able to see distant objects beyond 10 cm so, he should use a concave lens in his spectacles. The concave lens will form the image of object distant 30 cm, at 1.0 cm it means
u = -30 cm, v = -10 cm
f = - 15 cm (negative focal length means lens is concave)