Reflection and Mirrors

Light

• Light's speed varies depending on the medium through which it travels.

Reflection of Light

• Reflection occurs when light bounces back from surfaces.
• Plane mirrors create virtual, erect images with lateral inversion.
• Lateral inversion means the right and left sides of an image are reversed.
• The image size is the same as the object size in a plane mirror.
• The image distance from the mirror is the same as the object distance.

Concave and Convex Mirrors

• Concave mirrors and convex mirrors are types of curved mirrors.
• Key terms include pole, center of curvature, and focus.
• The pole is the center of the mirror's reflecting surface.
• The center of curvature is the center of the sphere from which the mirror was cut.
• The radius of curvature is the distance from the pole to the center of curvature.
• The focus is the point where parallel rays converge (concave) or appear to diverge from (convex).

Ray Diagrams

• Ray diagrams illustrate how light rays behave when they interact with mirrors.
• Light passing parallel to the principal axis goes through the focus after reflection.
• Light passing through the focus becomes parallel to the principal axis after reflection.
• Light rays passing through the center of curvature retrace their path.
• Light rays never meet in real life but virtually.

Image Formation by Concave Mirrors

• When an object is at the center of curvature, the image is real, inverted, and the same size.
• Placing an object between infinity and the pole in convex mirrors results in predictable light ray behavior.
• Concave mirrors create magnified images.

Uses of Concave Mirrors

• Concave mirrors can produce magnified images and are useful in various applications.

Mirror Formula

• The mirror formula relates object distance (u), image distance (v), and focal length (f): 1/f = 1/v + 1/u.
• Focal length (f) is half the radius of curvature (R): f = R/2.
• Concave mirrors have a negative focal length.
• Convex mirrors have a positive focal length.

Magnification

• Magnification (m) is the ratio of image height (h') to object height (h): m = h'/h = -v/u.
• Magnification indicates image type: positive for virtual and erect, negative for real and inverted.
• If |m| > 1, the image is magnified; if |m| < 1, the image is diminished.

Refraction of Light

• Refraction is the bending of light as it passes from one medium to another.
• Bending occurs due to changes in the speed of light in different media.
• Snell's Law describes the relationship between angles of incidence (i) and refraction (r): n₁sin(i) = n₂sin(r).
• The refractive index (n) indicates how much light bends when entering a medium.
• Light bends towards the normal when moving from a rarer to a denser medium.
• Light bends away from the normal when moving from a denser to a rarer medium.

Refractive Index

• Refractive index (n) = speed of light in vacuum / speed of light in medium.
• Higher refractive index means more bending.

Lenses

• Lenses are transparent objects that refract light.
• Convex lenses converge light rays.
• Concave lenses diverge light rays.

Lens Terminology

• Key terms include optical center, principal axis, and focal length.
• The optical center is the center of the lens where light passes straight through without bending.
• The principal axis is the imaginary line through the optical center.
• The focal length is the distance from the optical center to the focal point.

Image Formation by Lenses

• Concave lenses always form virtual, erect, and diminished images.
• Parallel light rays converge at the focus in a convex lens, forming images.

Uses of Lenses

• Concave lenses minimize the size of images.

Sign Conventions for Lenses

• Focal length of a concave lens is negative.
• Focal length of a convex lens is positive.

Lens Formula

• The lens formula relates object distance (u), image distance (v), and focal length (f): 1/f = 1/v - 1/u.

Power of a Lens

• Power (P) is the ability of a lens to converge or diverge light rays: P = 1/f (f in meters).
• The unit of power is diopters (D).
• Convex lenses have positive power.
• Concave lenses have negative power.
• Positive magnification indicates virtual and erect images.