Plane Mirror [Part 1]

Plane Mirror

A flat reflective surface that forms images using the law of reflection.

Image in a Plane Mirror

An image that is the same size, upright, and located behind the mirror.

Upright Image

An image that has the same vertical orientation as the object.

Image Size (Plane Mirror)

Equal to the size of the object.

Ray Diagram Method

A technique using reflected rays to locate the position of an image.

Reflected Rays

Light rays that bounce off the mirror following the law of reflection.

Backward Extension of Rays

Imaginary extension of reflected rays used to locate virtual images.

Image Location

The point where extended reflected rays appear to originate.

Virtual Image

An image formed where light rays appear to come from, but do not actually pass through

Cannot be projected onto a screen

Key Property of Virtual Image

Real Image

An image formed where light rays actually converge.

Can be projected onto a screen.

Key Property of Real Image

Object Distance (d_o)

Distance from the mirror to the object.

Image Distance (d_i)

Distance from the mirror to the image.

d_o = -d_i

Plane Mirror Distance Relation

P

(i)

P’

(ii)

A

(iii)

d_o

(iv)

B

(v)

Flat Mirror

(vi)

d_i

(vii)

Q

(viii)

Q’

(ix)

Object and image are on opposite sides of the mirror.

Interpretation of Sign Convention

Congruent Triangles (Mirror Geometry)

Triangles formed by object and image rays are equal, ensuring equal distances.

Equal Distance Property

Image is as far behind the mirror as the object is in front.

Point-by-Point Image Formation

An extended object forms an image by combining images of all its points.

Apparent Origin of Rays

Observer perceives rays as coming from behind the mirror.

Due to backward extension of reflected rays.

Why Image Is Seen Behind Mirror

Multiple Image Formation

Occurs when more than one mirror reflects light.

Image of an Image

An image formed by one mirror can act as an object for another.

Image 3

(1)

Image 1

(2)

Mirror 1

(3)

Object

(4)

Mirror 2

(5)

Image 2

(6)

Parallel Mirrors Setup

Two mirrors facing each other.

Infinite Images (Parallel Mirrors)

An infinite sequence of images can form due to repeated reflections.

Condition for Infinite Images

Object is not placed exactly midway between mirrors

Front–Back Inversion

Mirror reverses depth (front and back), not left and right physically.

Mirror Reversal Analogy

Like turning a glove inside out (right becomes left).

Successive Reflections Effect

Each reflection flips front/back relative to the previous image.

Right-Angle Mirrors (90°)

Two mirrors placed perpendicular to each other.

Three images are formed.

Number of Images (90° Mirrors)

Single Reflection Images

Images formed from reflection in only one mirror.

Double Reflection Image

Image formed by reflection from both mirrors

Ray Path Analysis

Tracing rays helps identify how many reflections occur

Image Behind Corner

Some images require looking “behind” mirror intersection.