Key relationship
i = r; virtual image distance = object distance.
Physics · Class 12
Plane mirror reflection
Ray Optics & Optical Instruments
The reflected ray remains in the plane of incidence and makes the same angle with the normal. Backward extensions locate an upright virtual image as far behind the mirror as the object is in front.
Open the interactive experiment →Plane mirror reflection
படுகோணமும் எதிரொளிப்புக் கோணமும் சமம். மெய்நிகர் பிம்பம் கண்ணாடிக்குப் பின்னால் சம தொலைவில் தோன்றும்.
Key notes, relationships and model limits
Remember
The reflected ray remains in the plane of incidence and makes the same angle with the normal. Backward extensions locate an upright virtual image as far behind the mirror as the object is in front.
Common trap
An image behind a plane mirror cannot be collected on a screen.
Model limits
Plane mirror in a uniform medium; rays follow straight lines between interactions. Incidence is measured from the horizontal normal in this drawing.
What you will learn
Trace a reflected ray and locate a plane-mirror image.
Try the experiment
Try both scenarios, change one control, and predict the result before checking the graph and readouts.
Think of it this way
Change one input while keeping the others fixed, as you would in a controlled experiment.
Worked example
An object 30 cm in front gives an image 30 cm behind the mirror.
Why this matters
The model connects plane mirror reflection with an observable reading. Check the equation and assumptions before applying it.
Before you start
SI units · algebra · graph reading
Check your understanding
A ray arrives at 35° from the normal. Its reflection angle is?
- 55°
- 35°
- 70°
Read the explanation
The law uses angles from the normal: r=i=35°.
Course connection: Class XII Chapter 9. Consult the roadmap for CBSE, NEET, JEE Main and Advanced scope.