Drawing Ray Diagrams For Plane Mirrors

Ray Diagrams

Ray diagrams for plane mirrors are a straightforward way to visualize how images are formed by reflection. These diagrams help in understanding the path taken by light rays from an object to our eyes after reflecting off a mirror.

Step-By-Step Guide To Drawing Ray Diagrams For Plane Mirrors

Step 1: Draw the Mirror and the Object

• Begin by drawing a straight line to represent the plane mirror. Label the line as the mirror.
• Choose a point or an object in front of the mirror. This is the object from which light rays will emanate. It’s common to represent the object as an arrow or a simple shape for clarity.

Step 2: Identify and Mark the Object Distance

• Measure the distance from the object to the mirror. This distance is known as the object distance, often denoted by $d_{o}$, identified as “Distance A” in this diagram.
• “Distance B” is the image distance or the distance from the image to the mirror.
• Distance A is equal to Distance B and the image size is the same size as the object size.
• It’s crucial to maintain a consistent scale if you’re drawing a diagram for calculation purposes.

Step 3: Draw Reflected Rays To The Image

• From the top of the image, draw two or more rays towards the mirror and the eye. These are the reflected rays, the paths of light traveling from the mirror.
  1. Ray 1: Aim this ray towards the top of the eye
  2. Ray 2: Aim this ray towards the bottom of the eye
• These rays should be straight lines that strike the mirror at an incident point.
• Behind the mirror, the reflected rays should be extended and the extensions are dotted or dashed to indicate that they are not actual paths of light but rather the perceived paths. Broken lines from the image to mirror indicate virtual rays.
• The image is virtual – Virtual image: Light rays do not actually meet at the image position. Because of that, a virtual image cannot be projected on a screen.

Step 4: Use Law Of Reflection To Work Out Incident Rays

• At the point of incident, we recall that according to the Law Of Reflection, the angle of incidence is equal to the angle of reflection. We direct the reflected ray back to the object, which will form the incident ray.
• Check that the angles are correct – angle of incidence is equal to the angle of reflection

Properties Of Image Formed In Plane Mirror

• Same size as object
• Laterally inverted (Left becomes right, right becomes left)
• Upright
• Virtual
• As far behind the mirror as the object is in front

Worked Examples

Question 1: Understanding Image Formation

Consider a plane mirror and an object placed 5 units in front of it. If a ray of light emanates from the top of the object and reflects off the mirror to an observer’s eye, how would you draw the ray diagram to locate the image? Describe the steps and the properties of the image formed.

Question 2: Critical Analysis of Ray Diagrams

Explain how the principle of laterally inverted images in plane mirrors is represented in ray diagrams. Use the concept of ray paths from an object to the observer’s eyes after reflection.

Question 3: Application of the Law of Reflection

A student draws a ray diagram with an angle of incidence of 30 degrees. However, the angle of reflection marked is 40 degrees. Critically evaluate this diagram in the context of the Law of Reflection. What corrections, if any, should be made?

Question 4: Depth Perception in Ray Diagrams

How does a ray diagram for a plane mirror explain the perception of depth, i.e., the distance behind the mirror where the image appears to be located? Illustrate this concept with a ray diagram involving an object placed 10 units in front of a plane mirror.