Correct option is D
Concept:
Optical flats are precision instruments used to measure the
flatness and
surface accuracy of a surface, not to measure angles. They work on the principle of interference of light waves and are commonly used in laboratories and precision workshops to inspect highly flat surfaces. When placed on the surface to be measured, they create interference patterns that indicate deviations from flatness. It uses transparent glass discs with precisely polished surfaces, used for checking surface flatness by observing light interference patterns.
Angular measurement involves the measurement of angles of tapers and similar surfaces. Examples:
· Bevel protector
· Sine Bar
· Spirit level
· Clinometer
· Autocollimators
· Protector's head
Clinometer: A device used to measure the inclination or angle of a surface relative to the horizontal plane.
Bevel Protractor: A precision instrument used to measure angles accurately, commonly in engineering and machining tasks.
Protractor Head: Part of a combination set used to measure angles on various surfaces, often in conjunction with a straight edge or rule.
