wiz-icon
MyQuestionIcon
MyQuestionIcon
1
You visited us 1 times! Enjoying our articles? Unlock Full Access!
Question

Why is object distance is considered negative while measuring optical distances?


Open in App
Solution

Sign convention:

The sign convention is a set of rules to set signs for image distance, object distance, focal length, etc for mathematical analysis of image formation.

Explanation:

  1. The object is always placed to the left of the lens.
  2. There is a pole in the mirror from which the distances are measured.
  3. Distances measured in the direction of the incident ray are positive and the distances measured in the direction opposite to that of the incident rays are negative.
  4. Distances measured along the y-axis above the principal axis are positive and that measured along the y-axis below the principal axis are negative.
  5. For instance, the focal length of the concave mirror is negative as it is being measured from the optical center in the opposite direction of the incident rays.

Because the rays of a concave mirror converge at a position upon that negative side of the origin, the overall focal length of the concave mirror is negative.

Hence, the object distance is always negative while measuring optical distances according to the sign conventions.


flag
Suggest Corrections
thumbs-up
4
Join BYJU'S Learning Program
similar_icon
Related Videos
thumbnail
lock
Power and Thin Lenses in Contact
PHYSICS
Watch in App
Join BYJU'S Learning Program
CrossIcon