The radii of curvature of a double convex lens are 4 cm and 8 cm . If the refractive index of the material of the lens is 1.5 , the focal length of the lens is nearly.
When monochromatic light of wavelength 600 nm is used in Young's double slit experiment, the fifth order bright fringe is formed at 6 mm from the central bright fringe on the screen. If the experiment is conducted with light of wavelength 400 nm from the central bright fringe, the third order bright fringe will be located at
A solid sphere of radius $$R$$ carries a positive charge $$Q$$ distributed uniformly throughout its volume. A very thin hole is drilled through it's centre. A particle of mass $$m$$ and charge $$-$$q performs simple harmonic motion about the centre of the sphere in this hole. The frequency of oscillation is
Assertion (A) In a region of constant potential, the electric field is zero and there can be no charge inside the region.
Reason (R) According to Gauss law, charge inside the region should be zero if electric field is zero.