The inside portion of part of a hollow metal sphere of diameter 20cm is polished. The portion will therefore form a
Answer Details
When a part of a hollow metal sphere is polished, it becomes reflective and can act as a mirror. The type of mirror it forms depends on the curvature of the surface. If the surface is curved inwards, it forms a concave mirror. If the surface is curved outwards, it forms a convex mirror. In this case, since the metal sphere is hollow and the inside portion is polished, the surface will be curved inwards, forming a concave mirror. To determine the focal length of this mirror, we need to know the radius of curvature of the mirror, which is half of the diameter of the original sphere. Thus, the radius of curvature is 10 cm. The focal length of a concave mirror is half of the radius of curvature, so the focal length of this mirror is 5 cm. Therefore, the answer is: concave mirror of focal length 5cm.