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General Science›Ch 1: Physics›Light: Reflection and Mirrors
Master laws of reflection, mirror formulas, and imaging characteristics for competitive exams.
Light travels in a straight line and bounces off surfaces following two strict laws of reflection. The angle of incidence is always equal to the angle of reflection, and the incident ray, normal, and reflected ray all lie in the same plane.
Quick Memory Hooks
| Mirror Type | Reflecting Surface | Image Nature | Key Application |
|---|---|---|---|
| Plane | Flat | Virtual, Equal | Looking glass |
| Concave | Inward curved | Real & Virtual | Headlights, ENT |
| Convex | Outward curved | Virtual & Diminished | Rearview mirror |
Pole (P)
(Center of surface)
Center of surface
The geometric center of the spherical mirror surface.
Focus (F)
(Principal convergence)
Principal convergence
Parallel light rays converge or appear to diverge from here.
Radius (R)
(Sphere radius)
Sphere radius
Radius of the hollow sphere of which mirror is a part.
Rearview
(Wide field view)
Wide field view
Convex mirrors give drivers an upright, wide traffic view.
Convex mirror forms real imagesConvex mirror always forms virtual images
Convex mirrors diverge light, creating only virtual and diminished images.
Focal length is equal to radiusFocal length is half of radius (f = R/2)
Always remember the exact relation: focal length is half the radius of curvature.
Plane mirror forms real imagesPlane mirror always forms virtual images
Images formed by plane mirrors cannot be caught on a screen.
Q1.Which mirror is commonly used as a rear-view mirror in vehicles?
Q2.If the radius of curvature of a spherical mirror is 20 cm, what is its focal length?