Images in Plane Mirrors - October 29, 2024

Using Light Rays to Locate an Image

  • Light rays and the laws of reflection help determine how and where an image is formed in a plane mirror

  • You already know that light travels in a straight line and because of this, when your eye detects reflected light off a plane mirror, your brain projects these light rays backward in a straight line to form an apparent light source

  • The rays are reflected off the mirror, with the angle of incidence being equal to the angle of reflection

  • TO SUMMARIZE:

    • The light from an object in front of a mirror has to travel to the mirror, and then bounce off it to return to your eyes

    • But your eyes can’t tell the difference between reflected and incident rays

      • Your brain thinks the light source behind the mirror and that’s where the light rays originate

    • Plus - your brain knows that light rays always travel in straight lines

    • That means that your brain thinks that the object is two times farther away than it actually is and is behind the mirror

  • Mirrors are opaque therefore there is no real light source behind them → called a virtual image

    • An image formed by light coming from an apparent light source

    • Light is not arriving at or coming from the image location;

    • Instead, light only appears to come from the image

Using Equal Perpendicular Lines to Locate an Image

  • Drawing object-image lines (lines drawn between the original object and the location of the image) can also be used to locate images without using light rays

  • TWO observations can be made:

    1. The distance from the object to the mirror is exactly the same as the distance from the image to the mirror → image appears to be located the same distance behind the mirror as the object is in front of the mirror

    2. The object-image line is perpendicular to the mirror surface

    • Therefore, a plane mirror divides the object-mage line in half and is perpendicular to that line

Characteristics of an Image in a Plane Mirror

  • This concept is referred to as “lateral inversion”

  • The orientation of an image in a plane mirror that is backwards (flipped horizontally) and in reverse order!

  • Images are reversed because light rays that hit a plane mirror are reflected right back along the same path

  • That means a point on your left side is reflected off the right side of the mirror - therefore making it look like the image is reversed when it returns to your eyes

The Acronym SALT

  • The four characteristics used to describe the properties of an image are as follows:

    • S = Size of image (same, smaller, or larger)

    • A = Attitude of image (upright or inverted)

    • L = Location of image

    • T = Type of image (real or virtual)