75. A astronomical telescope has objective and eyepiece of focal lengths 40 cm and 4 cm respectively. To view an object 200 cm away from the objective, the lenses must be separated by a distance :

62. The angle of incidence for a ray of light at a refracting surface of a prism is 45°. The angle of prism is 60°. If the ray suffers minimum deviation through the prism, the angle of minimum deviation and refractive index of the material of the prism respectively, are :

6. Match the corresponding entries of column-1 with column-2 (Where m is the magnification produced by the mirror) :

6. Match the corresponding entries of column-1 with column-2 (Where m is the magnification produced by the mirror) :

A capacitor of 2μF is charged as shown in the diagram. When the switch S is turned to position 2 , the percentage of its stored energy dissipated is ?

Two identical charged spheres suspended from a common point by two massless strings of lengths l, are initially at a distance d(d ≪ l) apart because of their mutual repulsion. The charges begin to leak from both the spheres at a constant rate. As a result, the spheres approach each other with a velocity v. Then v varies as a function of the distance x between the spheres, as: ?