There are some rules which we use to obtain images in a ray diagram

Let's look at them

Rule 1 - Ray parallel to principal axis will pass through focus


For a convex lens ,

we see that ray passes through focus on right side

For a concave lens,

we see that ray appears to pass through focus on left side


Rule 2 - Ray passing through focus will become parallel to principal axis


For a convex lens,

we see that ray passing through focus on left becomes parallel to principal axis after refraction


For a concave lens ,

since focus is on the right side,

it appears that ray passes through focus, and then it becomes parallel to principal axis


Rule 3 - Ray passing through Optical Center will emerge without deviation


For a both convex and concave lens,

we see that ray passing through Optical center emerges without deviation


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Davneet Singh
Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 9 years. He provides courses for Maths and Science at Teachoo.