Light: Reflection and Refraction

Basic Concepts

• Light as Energy: Travels in a straight line.
• Reflection: Bouncing back of light when it strikes a smooth surface like a mirror.
• Refraction: Change in direction of light when passing from one medium to another, altering its speed.

Reflection of Light

Mirrors

• Types:
  • Plane Mirror: Creates virtual images that are same size as the object, laterally reversed.
  • Spherical Mirrors:
    • Convex Mirror: Outward curved, diverging
    • Concave Mirror: Inward curved, converging

Terms in Spherical Mirrors

• Pole (P): Center point of the reflecting surface.
• Center of Curvature (C): Center of the sphere part of the mirror.
• Radius of Curvature (R): Radius of the sphere part.
• Principal Axis: Line joining pole and center of curvature.
• Principal Focus (F): Point where parallel rays converge (concave) or appear to diverge from (convex).
• Focal Length (f): Distance between pole and principal focus.
• Aperture: Diameter of the reflecting surface.

Image Formation by Concave Mirror

• Position & Nature: Varied based on object position (At infinity, Beyond C, At C, Between C and F, At F, Between P and F).
• Uses: Shaving mirrors, dentist mirrors, torch reflectors.

Image Formation by Convex Mirror

• Position & Nature: Typically virtual, erect, diminished.
• Uses: Rear-view mirrors in vehicles.

Sign Conventions

• Measurements from the pole, positive directions defined.

Mirror Formula and Magnification

• Formula: ( \frac{1}{v} + \frac{1}{u} = \frac{1}{f} )
• Magnification (M): ( M = \frac{h'}{h} = -\frac{v}{u} )

Refraction of Light

Basic Concepts

• Occurs when light speed changes due to medium change.
• Examples: Bent appearance in water, glass effects.

Laws of Refraction

• Incident Ray, Refracted Ray, and Normal lie in the same plane.
• Snell’s Law: ( \frac{\sin i}{\sin r} = \text{constant} )

Refractive Index

• Measure of light speed reduction in a medium.
• Examples: Water ~1.33, Diamond ~2.42.

Refraction by Spherical Lenses

Types of Lenses

• Convex (Converging): Thicker at center, converges light.
• Concave (Diverging): Thinner at center, diverges light.

Terms in Lenses

• Principal Axis: Line through centers of curvature.
• Optical Center (O): Central point.
• Principal Focus (F): Convergence point for convex, divergence for concave.
• Focal Length (f): Distance from optical center to principal focus.

Image Formation

• Convex Lens: Real, inverted images; virtual, erect possible when object is between focus and lens.
• Concave Lens: Typically virtual, erect, diminished images.

Lens Formula and Magnification

• Formula: ( \frac{1}{v} - \frac{1}{u} = \frac{1}{f} )
• Magnification (M): ( M = \frac{h'}{h} = \frac{v}{u} )

Power of a Lens

• Power (P): ( P = \frac{1}{f} )
• Units: Diopters (D)
• Significance: Positive for converging, negative for diverging lenses.