Read Images: Reflect, Locate, Then Trace
First decide whether the question is about a plane mirror or a converging lens. The image rules are different, but both depend on careful ray geometry.
Plane mirrors and converging lenses is the central idea in this question pattern. Identify the condition in the stem before applying the method below.
Trace the light ray before choosing an image
Trace the ray in the direction light travels
A ray travels from source to object and then to the eye. At a mirror, the angle of incidence equals the angle of reflection.
Use the plane-mirror distance rule
Image distance behind a plane mirror equals object distance in front.
Moving toward the mirror by x shortens the separation by 2x.
Trace the principal lens rays
For a converging lens, a ray parallel to the principal axis goes through the far focus; a ray through the optical centre is undeviated. As an object approaches the focal point from outside, the real image moves farther away and becomes larger.
Check what is always true
Plane mirrors make virtual, upright images. Parallel plane mirrors make many images whose brightness falls with repeated reflection; a converging lens does not always make the same type of image.
OlympIQ exam lens
- ✓Mark the mirror or lens before using a rule.
- ✓For a plane mirror, double the object–mirror distance.
- ✓For a lens ray diagram, use the focus and optical centre.
Do not treat a converging lens as if it always gives a real, inverted image: inside the focal length it gives a virtual, upright, magnified image.
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