Lesson 6: Locating Images in Mirrors

• The brain assumes that a light ray travels in a straight line. Therefore, to find out where
the eye “sees” the image, extend the rays that reach the eye backward until they meet at a
point behind the mirror.
• This image is called a virtual image.
Using Light Rays to locate an image in a plane mirror
• By applying the laws of reflection to rays going from the object, i.e. by drawing a ray diagram,
we can predict where the image will be and what the image will look like, i.e., it is possible to
predict the characteristics oft the image.
How to draw a ray diagram for an object placed in a plane mirror:
1. Draw a line to represent a mirror, add hatch marks to show the non-reflecting surface of the
mirror.
2. Draw the object as a vertical arrow in front of the plane mirror.
3. Draw an incident ray from the tip of the arrow at a 90 ◦ angle. Because this line is normal to
the mirror, the ____________________. Therefore, the ___________________ _____.
The reflected ray goes directly backward along the same line as the incident ray.
4. Draw a second incident ray at an angle to the mirror. At the point where the incident ray
hits the mirror, draw a normal. Measure the angle of incidence with a protractor. Using the
Law of reflection that the angle of reflection is equal to the angle of incidence, draw the
reflected ray.
5. Using a dashed line, extend both the reflected rays behind the mirror until they cross one
another at the same point, i.e. at the point where they meet – this point is the image of the
arrow tip.
* _____________________________________.