Which measuring instrument consists of a metal triangular frame supported on three legs, used to measure the radius of curvature of an object such as lenses and curved mirrors which are spherical in shape?

Spherometer

The correct answer is option 2. Spherometer.

The measuring instrument consisting of a metal triangular frame supported on three legs, used to measure the radius of curvature of an object such as lenses and curved mirrors which are spherical in shape, is called a Spherometer.

A spherometer is specifically designed for measuring the radius of curvature (or sometimes the focal length) of spherical surfaces. It consists of a metal triangular frame with three legs, each ending in a fine point. By placing the spherometer on the surface whose radius of curvature needs to be measured and adjusting the central screw until all three legs touch the surface simultaneously, the radius of curvature can be determined based on the screw adjustment. Spherometers are commonly used in optics laboratories for precise measurements of lenses and curved mirrors.