Reflection of Light

Reflection is the bouncing back of light rays from a surface. It follows laws where angle of incidence equals reflection, and rays lie in the same plane. Example: Seeing your image in a plane mirror due to regular reflection.

Laws of Reflection

Laws state that the angle of incidence equals the angle of reflection, and the incident ray, normal, and reflected ray are coplanar. These apply to all reflecting surfaces. Example: In plane mirrors, images form following these laws, appearing equidistant.

Spherical Mirror

A spherical mirror has a reflecting surface that is part of a sphere. It can be concave (inwards) or convex (outwards). Example: Concave mirrors in torches focus light into beams.

Concave Mirror

A concave mirror curves inwards, converging light rays. It forms real or virtual images based on object position. Example: Used in shaving mirrors for enlarged face images.

Convex Mirror

A convex mirror curves outwards, diverging light rays. It always forms virtual, diminished images. Example: Rear-view mirrors in vehicles for wider field of view.

Pole

The pole is the center of the reflecting surface of a spherical mirror. It is denoted by P and lies on the surface. Example: The point where the principal axis meets the mirror.

Centre of Curvature

The centre of curvature is the center of the sphere from which the mirror is cut. Denoted by C, it lies outside the mirror. Example: For concave, in front; convex, behind.

Radius of Curvature

The radius of curvature is the radius of the sphere, equal to distance from pole to centre (R). It is twice the focal length. Example: R=2f relation for small apertures.

Principal Axis

The principal axis is the straight line passing through the pole and centre of curvature. It is normal to the mirror at the pole. Example: Used as reference for ray diagrams.

Principal Focus

The principal focus is where parallel rays converge (concave) or appear to diverge from (convex). Denoted by F. Example: Sunlight focuses at F in concave mirrors.

Focal Length

Focal length is the distance from pole to focus (f). It is half the radius of curvature. Example: Measured by focusing distant object.

Aperture

Aperture is the diameter of the reflecting surface. It is small compared to radius for approximations. Example: MN in diagrams represents aperture.

Real Image

A real image forms where rays actually converge, inverted, on screen. Formed by concave mirrors for most positions. Example: Projected movie on screen.

Virtual Image

A virtual image forms where rays appear to diverge from, erect, cannot be on screen. Formed by plane and convex mirrors. Example: Image in plane mirror.

Ray Diagram

A ray diagram shows paths of light rays to locate images. Uses specific rays like parallel, through focus. Example: Two rays intersect to find image point.

Laterally Inverted

Laterally inverted means left-right reversal in image. Occurs in plane mirrors. Example: Raised right hand appears left in mirror.

Diminished Image

A diminished image is smaller than the object. Formed by convex mirrors always. Example: Distant objects in rear-view mirrors appear smaller.

Enlarged Image

An enlarged image is larger than the object. Formed by concave mirrors close. Example: Magnified teeth in dental mirrors.

On Light Path

"Light seems to travel in straight lines."

Reflection Laws

"The angle of incidence is equal to the angle of reflection."

Spherical Mirrors

"R = 2f."

Image Nature

"Image formed by a plane mirror is always virtual and erect."

Uses

"Concave mirrors are used to concentrate sunlight."

Activity 9.1: Observing Images in a Shining Spoon

Steps: 1. Take a large shining spoon and view your face in its curved surface. 2. Note if the image is smaller or larger. 3. Move the spoon slowly away from your face and observe how the image changes. 4. Reverse the spoon to use the other surface and repeat the activity. 5. Compare the characteristics of the images on the two surfaces.
Observations: On inwards curved surface (concave), image enlarged when close, inverted when far; on outwards (convex), always diminished and erect.
Conclusion: Curved surfaces act as spherical mirrors; concave can magnify or invert, convex always diminishes, demonstrating different image formations.

Activity 9.2: Determining Focal Length of Concave Mirror

Steps: 1. Hold a concave mirror towards the Sun, directing reflected light on a paper sheet. 2. Move the paper back and forth until a bright, sharp spot appears. 3. Hold in position for a few minutes and observe. Caution: Do not look directly at Sun or reflection.
Observations: Paper begins to burn with smoke, may catch fire; spot is sharp and bright.
Conclusion: Concave mirror converges sunlight at focus, producing heat; distance from mirror to spot is approximate focal length, showing converging property.

Activity 9.3: Image Formation by Concave Mirror for Different Positions

Steps: 1. Find approximate focal length using Sun. 2. Mark lines on table for P, F, C (f apart). 3. Place mirror on stand over line. 4. Place burning candle far beyond C, move screen for sharp image. 5. Note nature, position, size. 6. Repeat for just beyond C, at C, between F C, at F (no screen, virtual), between P F (look in mirror). Tabulate.
Observations: Positions give real inverted diminished/enlarged, or virtual erect enlarged; one case no screen image.
Conclusion: Image nature, position, size depend on object position; real for distant, virtual for close, confirming table summary.

Activity 9.4: Drawing Ray Diagrams for Concave Mirror

Steps: 1. Draw neat ray diagrams for each object position in table. 2. Use any two rays: parallel, through F, through C, to P. 3. Compare with given figures. 4. Describe nature, position, relative size. Tabulate.
Observations: Diagrams match: e.g., beyond C image between F C inverted diminished.
Conclusion: Ray diagrams locate images accurately; confirm theoretical positions and natures for concave mirrors.

Activity 9.5: Observing Image in Convex Mirror

Steps: 1. Hold convex mirror in one hand. 2. Hold pencil upright in other. 3. Observe image: erect or inverted? Diminished or enlarged? 4. Move pencil away slowly: smaller or larger? 5. State if image moves closer or farther from focus as object moves away.
Observations: Image erect, diminished; becomes smaller as object moves away, approaches focus.
Conclusion: Convex mirrors always form virtual, erect, diminished images; size decreases with distance, useful for wide views.

Activity 9.6: Viewing Distant Object in Plane Mirror

Steps: 1. Observe a distant object like a tree in a plane mirror. 2. Check if you can see a full-length image.
Observations: Full image not visible unless mirror is large enough or tilted.
Conclusion: Plane mirrors give full images but require sufficient size; compare to curved mirrors which distort or diminish.

Introduction: Phenomena Associated with Light

• Visible reflected light; straight path; diffraction wave.
• Quantum duality; study reflection refraction rays.

9.1 Reflection of Light

• Laws: i=r, coplanar; plane virtual erect same inverted.

9.2 Spherical Mirrors

• Concave converge, convex diverge; P, C, R, axis.

Principal Focus and Focal Length

• F converge/diverge; f=PF, R=2f; aperture small.

9.2.1 Image Formation by Spherical Mirrors

• Concave positions: Real inverted distant, virtual erect close.

9.2.2 Representation Using Ray Diagrams

• Rays: Parallel F, F parallel, C back, P equal.

Uses of Concave Mirrors

• Beams, magnified, solar heat.

Image Formation by a Convex Mirror

• Always virtual erect diminished.