Calculator Form
Large screens show three columns, smaller screens show two, and mobiles show one.
Formula Used
Core Reflection Relations
Law of reflection: θr = θi
Glancing angle: θg = 90° − θi
Angle between incident and reflected rays: θbetween = 2θi
Reflection deviation: θdev = 180° − 2θi
Reverse Calculations
From reflected angle: θi = θr
From glancing angle: θi = 90° − θg
From angle between rays: θi = θbetween / 2
From deviation: θi = (180° − θdev) / 2
Mirror Rotation Case
When the mirror rotates while the incoming ray stays fixed, the reflected ray rotates by twice the mirror rotation magnitude. The exact new reflection direction here is found with vector reflection, making the graph and outputs more accurate.
How to Use This Calculator
Step 1: Choose the calculation mode that matches your known value.
Step 2: Enter the given angle in degrees.
Step 3: Pick the number of decimal places you want.
Step 4: Click the calculate button to display the result section.
Step 5: Review the table, cards, and graph below the header.
Step 6: Download the results as CSV or PDF if needed.
Example Data Table
| Example | Known Input | Incidence | Reflected | Glancing | Between Rays | Deviation |
|---|---|---|---|---|---|---|
| Incidence mode | 25° | 25° | 25° | 65° | 50° | 130° |
| Reflected mode | 19° | 19° | 19° | 71° | 38° | 142° |
| Glancing mode | 58° | 32° | 32° | 58° | 64° | 116° |
| Between rays mode | 84° | 42° | 42° | 48° | 84° | 96° |
| Deviation mode | 104° | 38° | 38° | 52° | 76° | 104° |
FAQs
1. What is the incidence angle?
It is the angle between the incoming ray and the normal line at the point of reflection. It is not measured from the mirror surface.
2. Why is the reflected angle equal to the incidence angle?
A plane mirror follows the law of reflection. That law states the reflected angle always equals the incidence angle when both are measured from the normal.
3. What is the glancing angle?
The glancing angle is measured between the ray and the mirror surface. It complements the incidence angle, so both add up to 90°.
4. What does angle between rays mean here?
It is the included angle formed by the incident and reflected rays. For a plane mirror, this value equals twice the incidence angle.
5. What is reflection deviation?
Reflection deviation is the angle between the reflected ray and the straight extension of the incoming ray. It equals 180° minus twice the incidence angle.
6. Why does the reflected ray rotate twice as much as the mirror?
When the mirror rotates and the incoming ray stays fixed, the normal rotates equally. Because reflection stays symmetric about the normal, the outgoing ray swings by twice that amount.
7. Can I use this for curved mirrors?
This page is intended for local reflection geometry and plane-mirror style angle work. Curved mirrors need additional geometry involving the local normal and mirror shape.
8. Which unit does this calculator use?
All inputs and outputs use degrees. If your source values are in radians, convert them to degrees before entering them here.
Why This Tool Helps
This calculator lets you solve standard mirror-angle questions quickly and also explore beam movement after mirror rotation.