⚡ Laws of Reflection
Complete Formula Sheet & Reference Guide
📋 Quick Overview
Reflection occurs when light bounces off a surface. The behavior follows specific laws that govern how light rays change direction when they encounter different types of mirrors and surfaces.
Law 1: Angle Equality
Statement: The angle of incidence equals the angle of reflection.
Where:
- ∠i = Angle of incidence (angle between incident ray and normal)
- ∠r = Angle of reflection (angle between reflected ray and normal)
Law 2: Coplanar Condition
Statement: The incident ray, reflected ray, and the normal to the surface at the point of incidence all lie in the same plane.
1. Mirror Formula
Where:
- f = Focal length of the mirror
- v = Image distance from the mirror
- u = Object distance from the mirror
Alternative forms:
- v = uf/(u+f) (Finding image distance)
- u = vf/(v-f) (Finding object distance)
- f = uv/(u+v) (Finding focal length)
2. Magnification Formula
Where:
- m = Magnification
- h' = Height of image
- h = Height of object
Image size formula: h' = m × h
3. Radius-Focal Length Relationship
Where:
- R = Radius of curvature
- f = Focal length
Plane Mirror Properties
• Image distance = Object distance
• Magnification = +1
• Image is virtual and erect
Multiple Images Formula:
Where: n = number of images, θ = angle between mirrors
Distances
Object distance (u): Always negative
Image distance (v):
• Real image: Positive
• Virtual image: Negative
Focal length (f):
• Concave mirror: Positive
• Convex mirror: Negative
Heights & Magnification
Object height (h): Always positive
Image height (h'):
• Erect image: Positive
• Inverted image: Negative
Magnification (m):
• Real image: Negative
• Virtual image: Positive
Angular Deviation
Where:
- δ = Deviation angle
- i = Angle of incidence
Special cases:
- Normal incidence (i = 0°): δ = 180°
- Grazing incidence (i = 90°): δ = 0°
Special Object Positions (Concave Mirror)
At Infinity (u = ∞)
Image: At focus (v = f), Real, Inverted, Highly diminished
Beyond Center of Curvature (u > 2f)
Image: Between f and 2f, Real, Inverted, Diminished
At Center of Curvature (u = 2f)
Image: At 2f (v = 2f), Real, Inverted, Same size (m = -1)
Between f and 2f
Image: Beyond 2f, Real, Inverted, Enlarged
At Focus (u = f)
Image: At infinity, Real, Inverted, Highly enlarged
Between Pole and Focus (u < f)
Image: Behind mirror, Virtual, Erect, Enlarged
| Mirror Type | Focal Length | Image Nature | Uses |
|---|---|---|---|
| Plane Mirror | ∞ (infinite) | Virtual, Erect, Same size | Dressing mirrors, Periscopes |
| Concave Mirror | Positive (+f) | Real/Virtual (depends on position) | Shaving mirrors, Headlights |
| Convex Mirror | Negative (-f) | Virtual, Erect, Diminished | Rear-view mirrors, Security mirrors |
🎯 Remember VINOD for Mirror Formula:
Very Important: Never Omit Distances
1/v + 1/u = 1/f
🎯 Sign Convention Trick:
LEFT side of mirror = NEGATIVE
RIGHT side of mirror = POSITIVE
🎯 Magnification Memory:
Minus V Upon U = m = -v/u
Height Image Upon Height Object = m = h'/h
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