.png "NOTES Class 10 Science chapter 9: Light – Reflection and Refraction -1") |
| Reflection of Light |
Introduction to Light – Reflection and Refraction
Light is a form of energy that allows us to perceive the world around us. Understanding how light interacts with different surfaces is crucial in physics. Two primary phenomena associated with light are reflection and refraction.
Reflection of Light
When light rays strike a surface and bounce back, it's called reflection. A highly polished surface, like a mirror, reflects most of the light. Reflection follows specific laws:
Laws of Reflection:
- First Law: The angle of incidence equals the angle of reflection.
- Second Law: The incident ray, the normal to the mirror at the point of incidence, and the reflected ray lie in the same plane.
These laws apply to all types of reflecting surfaces, including plane and spherical mirrors.
Image Formation by Plane Mirrors
Images formed by plane mirrors possess distinct characteristics:
- Virtual and Erect: The image is upright and cannot be captured on a screen.
- Same Size: It is of the same size as the object.
- Laterally Inverted: Left and right are reversed compared to the object.
- Equal Distance: The image is as far behind the mirror as the object is in front of it.
Activity 9.1: Exploring Curved Surfaces
- Take a large, shiny spoon and observe your face in its curved surface.
- Note the image size and how it changes with varying distances.
- Compare images seen on concave and convex surfaces.
This activity illustrates how curved surfaces create images differently from plane mirrors.
Spherical Mirrors
Spherical mirrors are parts of a sphere's surface and come in two types:
- Concave Mirrors: Inward-curved reflecting surfaces.
- Convex Mirrors: Outward-curved reflecting surfaces.
Key Terms Related to Spherical Mirrors
- Pole (P): Center of the mirror's reflecting surface.
- Center of Curvature (C): Sphere's center of which the mirror is a part; for concave mirrors, it's in front, for convex, behind.
- Radius of Curvature (R): Sphere's radius of which the mirror forms a part.
- Principal Axis: Straight line through the pole and center of curvature.
- Principal Focus (F): Point where parallel rays converge (concave) or appear to diverge (convex).
- Focal Length (f): Distance from pole to principal focus.
Activity 9.2: Determining Focal Length
- Hold a concave mirror towards the Sun.
- Reflect sunlight onto a paper and adjust until a sharp bright spot forms.
- Measure distance from mirror to spot to find focal length.
This demonstrates how concave mirrors converge light rays.
Ray Diagrams for Spherical Mirrors
Ray diagrams aid in understanding image formation by concave and convex mirrors using specific rays:
- Ray Parallel to Principal Axis: After reflection, passes through (concave) or appears to diverge from (convex) principal focus.
- Ray Through Principal Focus: After reflection, emerges parallel to principal axis.
- Ray through Center of Curvature: Reflects back along the same path due to perpendicular strike.
Image Formation by Concave Mirrors
- Object at Infinity: Image formed at focus (F), highly diminished, real, and inverted.
- Object Beyond Center of Curvature (C): Image between F and C, diminished, real, and inverted.
- Object at C: Image at C, same size, real, and inverted.
- Object between F and C: Image beyond C, enlarged, real, and inverted.
- Object at F: Image at infinity, highly enlarged, real, and inverted.
- Object between P and F: Image behind mirror, enlarged, virtual, and erect.
Uses of Concave Mirrors
- Torches, Searchlights, and Headlights: Produce powerful parallel beams.
- Shaving Mirrors: Enlarge facial images.
- Dentists' Mirrors: Enlarge views of teeth.
- Solar Furnaces: Concentrate sunlight to produce heat.
Image Formation by Convex Mirrors
- Object at Infinity: Image at focus (F), highly diminished, virtual, and erect.
- Object at Finite Distance: Image between F and P, diminished, virtual, and erect.
Uses of Convex Mirrors
- Vehicle Rear-View Mirrors: Wider field of view for drivers.
- Street Light Reflectors: Spread light over large areas
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