🌟 Chapter: Light – Full Explanation
1️⃣ Introduction to Light
- Light is a form of energy.
- It enables us to see objects.
- It travels in a straight line.
- It exhibits phenomena like reflection, refraction, dispersion, and absorption.
2️⃣ Definition of Light
Light is an energy that travels in the form of waves and enables us to see the objects around us by entering our eyes after reflecting from them.
3️⃣ Sources of Light
a. Luminous Objects
- Emit their own light.
- Examples: Sun, candle, bulb.
b. Non-luminous Objects
- Do not emit their own light.
- We can see them because they reflect light.
- Examples: Moon, book, table.
4️⃣ Types of Objects Based on Transparency
| Type | Definition | Example |
|---|---|---|
| Transparent | Allow light to pass completely | Glass window |
| Translucent | Allow partial light | Frosted glass |
| Opaque | Do not allow light to pass | Wood, wall |
5️⃣ Light Ray and Beam
➤ Light Ray
- A narrow straight path along which light travels.
- Represented by a straight line with an arrow.
➤ Light Beam
- A collection of light rays.
- Types of beams:
- Parallel Beam
- Divergent Beam
- Convergent Beam
6️⃣ Image and Its Types
What is an Image?
➤An image is a visual representation of an object formed when light rays coming from the object reflect or refract.
➤ Types of Image
| Type | Description | Example |
|---|---|---|
| Real Image | Can be captured on a screen | Shadow, cinema |
| Virtual Image | Cannot be captured on screen | Mirror image |
7️⃣ Characteristics of Images
| Image Type | Can Be Caught on Screen? | Orientation | Size | Formed By |
|---|---|---|---|---|
| Real | Yes | Inverted | Small/large | Concave mirror, lens |
| Virtual | No | Erect | Same/diminished | Plane mirror, convex mirror |
8️⃣ Mirrors
A mirror is a smooth and polished surface that reflects light.
➤ Types of Mirrors
-
Plane Mirror
-
Spherical Mirror
- Concave (Converging)
- Convex (Diverging)
9️⃣ Plane Mirror
➤ Characteristics of Image Formed:
- Virtual and erect
- Laterally inverted
- Same size as object
- Image appears as far behind the mirror as the object is in front
🔟 Spherical Mirrors
What are Spherical Mirrors?
➤A spherical mirror is a mirror that is part of a sphere.
➤ Types:
1. Concave Mirror
- Inner side is reflecting.
- Converges light.
- Used in: torches, shaving mirrors, dentist mirrors.
2. Convex Mirror
- Outer side is reflecting.
- Diverges light.
- Used in: rear-view mirrors, ATMs.
🔢 Important Terms Used in Spherical Mirrors
| Term | Description |
|---|---|
| Pole (P) | Center of mirror's surface |
| Centre of Curvature (C) | Center of the sphere of which the mirror is a part |
| Radius of Curvature (R) | Distance between C and P |
| Principal Axis | Line joining the pole and centre of curvature |
| Focus (F) | Point where parallel rays meet after reflection |
| Focal Length (f) | Distance between pole and focus |
| Aperture | Width of the mirror’s surface |
🔁 Rules for Drawing Ray Diagrams
✅ Concave Mirror:
- Ray parallel to principal axis → passes through focus.
- Ray passing through focus → reflects parallel.
- Ray through center of curvature → reflects back along same path.
✅ Convex Mirror:
- Ray parallel to principal axis → appears to diverge from focus.
- Ray aimed at center of curvature → reflects back along the same path.
- Ray aimed at pole → reflects at equal angle.
🔄 Image Formation by Spherical Mirrors
🔹 Concave Mirror:
| Object Position | Image Nature |
|---|---|
| At Infinity | Point-sized, real, inverted at focus |
| Beyond C | Small, real, inverted, between F and C |
| At C | Same size, real, inverted, at C |
| Between C and F | Enlarged, real, inverted, beyond C |
| At F | No image (rays parallel) |
| Between P and F | Enlarged, virtual, erect, behind mirror |
🔹 Convex Mirror:
| Object Position | Image Nature |
|---|---|
| At Infinity | Point-sized, virtual, erect at focus |
| Anywhere on Axis | Small, virtual, erect, behind mirror |
⚖️ Laws of Reflection of Light
- Angle of incidence = Angle of reflection
- Incident ray, reflected ray, and normal lie in the same plane
📌 These laws hold true for both plane and spherical mirrors.
Terminology of reflection
Incident ray: The ray of light falling on the surface of a mirror is known as an incident ray.
Point of incidence: The point where incident rays touch the surface of a mirror is
called a point of incidence.
Reflected ray: The ray of light that bounces off from the mirror surface is called a
reflected ray.
Normal: The perpendicular line drawn at the point of incidence to the surface of
a mirror is called normal.
Angle of incidence: The angle between the incident ray and the normal at the point
of incidence is called the angle of incidence.
Angle of reflection: The angle between the reflected ray and the normal at the
point of incidence is called the angle of incidence.
Laws of Reflection
The laws of reflection determine the reflection of incident rays on the surfaces
such as mirrors, smooth metal surfaces, and clear water. Here we are considering
a plane mirror as shown in the figure below.
Basically, there are two types of laws of reflection:
Law 1. The incident ray, the reflected ray, and the normal, all lie in the same plane.
Law 2. The angle of incidence is equal to the angle of reflection. ∠i = ∠r
📊 Summary Chart
| Mirror Type | Image Type | Orientation | Size | Usage |
|---|---|---|---|---|
| Plane | Virtual | Erect | Same | Mirrors at home |
| Concave | Real/Virtual | Inverted/Erect | Varies | Dentist, headlights |
| Convex | Always Virtual | Always Erect | Diminished | Rear-view mirrors |
📎 Extra Tips:
- Lateral Inversion: Left appears as right in mirror.
- Concave mirrors can form both real and virtual images.
- Convex mirrors always form virtual, erect, and smaller images.