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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