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Reflection of Light
Reflection means light returns from a surface. The key law is `i = r`.
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Reflection of Light
Light can bounce back from a surface.
A mirror is the easiest example.
Remember one main rule:
**angle in = angle out**
but both angles are measured from the normal.
Recommended for Class 10
Reflection of Light
Reflection of light is the return of light into the same medium after it strikes a surface.
When a ray of light reaches a mirror, part of the light can be reflected back.
The incoming ray is called the incident ray, and the returning ray is called the reflected ray.
Normal
A normal is an imaginary line drawn perpendicular to the reflecting surface at the point where the incident ray strikes it.
Angles in reflection are measured from the normal, not from the mirror surface.
Angle of Incidence
The angle between the incident ray and the normal is called the angle of incidence, represented by i.
Angle of Reflection
The angle between the reflected ray and the normal is called the angle of reflection, represented by r.
Laws of Reflection
The first law states:
Angle of incidence = Angle of reflection
**i = r**
The second law states that the incident ray, reflected ray, and normal all lie in the same plane.
Regular Reflection
A smooth surface such as a plane mirror reflects parallel incident rays in an orderly way.
This is called regular or specular reflection.
It can produce a clear image.
Diffuse Reflection
A rough surface reflects incoming light in many different directions because different parts of the surface have different orientations.
This is called diffuse reflection.
The law of reflection still applies at each small part of the surface.
Plane-Mirror Image
A plane mirror produces an image that is:
virtual; upright; approximately the same size as the object; laterally inverted; * as far behind the mirror as the object is in front.
Reflection of Light — Advanced
Reflection can be understood geometrically using rays and wavefronts.
For a plane reflecting surface, the equality `i = r` follows from the symmetry of the incident and reflected paths.
Diffuse reflection does not mean random failure of the reflection law; rather, microscopic changes in surface orientation produce reflected rays in different macroscopic directions.
Common Mistakes
Common Mistakes
- Mistake
Mistake: Angles are measured from the mirror. Correction: Measure them from the normal.
- Mistake
Mistake: Diffuse reflection breaks the laws of reflection. Correction: Each small surface region still obeys `i = r`.
- Mistake
Mistake: A plane-mirror image can normally be projected onto a screen. Correction: It is a virtual image.
Revision Zone
60-Second Revision
Quick cues from this topic — use them for last-minute revision.
Reflection → light returns into same medium.
**i = r**
Angles measured from normal.
Plane mirror → virtual + upright + same size.
- Definition
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Practice
PQ
Q1. Define reflection of light.
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Q2. State the first law of reflection.
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Q3. From where are reflection angles measured?
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Q4. State four properties of a plane-mirror image.
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Q5. Why can a rough wall still reflect light?
Exam Practice
EQ
Q1. Define reflection and state its laws.
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Q2. Define the normal.
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Q3. Differentiate regular and diffuse reflection.
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Q4. State four properties of an image in a plane mirror.
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Q5. A ray strikes a mirror at an incidence angle of 42°. Find the reflection angle.
School-standard facts for Matric and Intermediate. Original explanations — not copied from textbooks.