The same size images are formed by a convex lens by a convex lens when the object is placed at 20cm or at 10cm from the lens. The focal length of convex lens is ……………cm.

When a soap bubble is illuminated by source of white light, it appears coloured. This is due to

If the earth suddenly stop rotating, the value of ‘g’ at the equator would

Energy required to shift a body of mass m from an orbit of radius 2R to 3R is (mass of planet is M)

The radii of circular orbits of two satellites A and B of the earth, are 4R and R, respectively. If speed of satellite A is 2V, then the speed of satellite B will be

A wire can be broken by a load of 20 kg-wt. The force required to break wire of same material with twice the diameter will be