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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

rule-1---ray-parallel-to-principal-axis-will-pass-through-focus-2---teachoo.jpg

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

rule-2---ray-passing-through-focus-will-become-parallel-to-principal-axis---teachoo.jpg

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

rule-3---ray-passing-through-optical-center-will-emerge-without-deviation---teachoo.jpg

For a both convex and concave lens,

we see that ray passing through Optical center emerges without deviation

 

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CA Maninder Singh

CA Maninder Singh is a Chartered Accountant for the past 12 years and a teacher from the past 16 years. He teaches Science, Accounts and English at Teachoo