To obtain the powerful parallel beams of light from a vehicle's headlight, one must use
Two thin convex lenses of focal lengths 4 cm and 8 cm are separated by a distance of 4 cm in air. The combination will have the focal length
Two metallic wires A and B are of same material and have equal length. If the cross-sectional area of B is double that of A, then which one among the following is the electrical resistance of B?
The torque on a rectangular coil placed in a uniform magnetic field is large when the
The thermal conductivity of copper is 4 items that of brass. Two rods of copper and brass having same length and cross-section are joined end to end. The free end of copper is at 0o C and the free end of brass is at 100o C. The temperature of the junction is
If the focal length of the biconvex lens is 25 cms, then the power of the lens will be