From the following, what charges can be present on oil drops in Millikan's experiment (Here e is the electronic charge)
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(a) Zero, equal to the magnitude of charge on α - particle |
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(b) 2e, 1.6 |
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(c) 1.6 |
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(d) 1.5 e, e |
(b) 2e, 1.6 
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For the structural analysis of crystals, X-rays are used because
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(a) X-rays have wavelength of the order of interatomic spacing |
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(b) X-rays are highly penetrating radiations |
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(c) Wavelength of X-rays is of the order of nuclear size |
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(d) X-rays are coherent radiations |
If the distance of the far point for a myopia patient is doubled, the focal length of the lens required to cure it will become
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(a) Half |
(b) Double |
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(c) The same but a convex lens |
(d) The same but a concave lens |
Which one of the following devices makes use of the electrons to strike certain substances to produce fluorescence
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(a) Thermionic valve |
(b) Photoelectric cell |
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(c) Cathode ray oscilloscope |
(d) Electron gun |
Assertion : Magnetic field interacts with a moving charge and not with a stationary charge.
Reason : A moving charge produces a magnetic field.
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(a) If both assertion and reason are true and the reason is the correct explanation of the assertion. |
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(b) If both assertion and reason are true but reason is not the correct explanation of the assertion. |
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(c) If assertion is true but reason is false. |
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(d) If the assertion and reason both are false. |
Assertion : The ferromagnetic substance do not obey Curie’s law.
Reason : At Curie point a ferromagnetic substance start behaving as a paramagnetic substance.
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(a) If both assertion and reason are true and the reason is the correct explanation of the assertion. |
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(b) If both assertion and reason are true but reason is not the correct explanation of the assertion. |
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(c) If assertion is true but reason is false. |
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(d) If the assertion and reason both are false. |
A charge particle is free to move in an electric field. It will travel
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(a) Always along a line of force |
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(b) Along a line of force, if its initial velocity is zero |
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(c) Along a line of force, if it has some initial velocity in the direction of an acute angle with the line of force |
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(d) None of the above |
