In a parallel plate capacitor with air between the plates, the distance $$d$$ between the plates is changed and the space is filled with dielectric constant 8. The capacity of the capacitor is increased 16 times, the distance between the plates is

A ray of light passes through an equilateral prism such that the angle of incidence $$(i)$$ is equal to angle of emergence $$(e)$$. The angle of emergence is equal to $$\left(\frac{3}{4}\right)$$th the angle of prism. The angle of deviation is

The radii of curvature of both the surfaces of a convex lens of focal length $$f$$ and power $$P$$ are equal. One of the surfaces is made by plane grinding. The new focal length and focal power of the lens is

A spring balance is attached to the ceiling of a lift. A man hangs his bag on the spring and the spring balance reads $$49 \mathrm{~N}$$, when the lift is stationary. If the lift moves downward with an acceleration of $$5 \mathrm{~m} / \mathrm{s}^2$$, the reading of the spring balance will be $$\left(g=9.8 \mathrm{~m} / \mathrm{s}^2\right)$$