Light Reflection and Refraction Lecture Notes

Introduction to Light

• Light is a form of energy and travels in a straight line.

Reflection of Light

• Definition: When a light ray strikes a smooth, polished surface like a mirror, it bounces back. This is known as reflection.
• Mirrors: Opaque objects with shiny reflective surfaces that allow us to see images through reflection.

Plane Mirrors

• Law of Reflection: Angle of reflection = Angle of incidence.
• Image Formation:
  • Virtual images formed behind the mirror.
  • Same size as the object; no magnification.
  • Images are laterally reversed (left-right reversed).

Spherical Mirrors

• Types:
  • Convex Mirror: Outward curved reflective surface.
  • Concave Mirror: Inward curved reflective surface.

Key Terms

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

Ray Diagrams for Spherical Mirrors

• Concave Mirrors:
  • Different object positions result in real and inverted images except when the object is between P and F, resulting in virtual and erect image.
• Convex Mirrors: Always forms virtual, diminished, and erect images behind the mirror.

Uses

• Concave Mirrors: Shaving mirrors, dentist mirrors, torch reflectors.
• Convex Mirrors: Rear-view mirrors in vehicles.

Sign Convention

• Distances are measured from the pole of the mirror.
• Positive distances: right of the pole; Negative: left of the pole.
• Heights above principal axis: positive; below: negative.

Mirror Formula

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

Refraction of Light

• Definition: Change in direction of light when passing from one medium to another.

Refraction in Daily Life

• Phenomena like bending of a straw in water or enlarged appearance of objects underwater.

Laws of Refraction

1. Incident ray, refracted ray, and normal lie in the same plane.
2. Snell’s Law: ( \frac{\sin i}{\sin r} = \text{constant} )

Refractive Index

• Measures speed reduction of light in a medium.
• Formula: ( n_{21} = \frac{v_1}{v_2} )
• Absolute refractive index: ( n_m = \frac{c}{v} )_

Refraction by Spherical Lenses

• Lens Types:
  • Convex Lens: Converging, thicker at center.
  • Concave Lens: Diverging, thinner at center.

Key Terms for Lenses

• Principal Focus (F): Point where rays meet.
• Optical Center (O): Center of the lens.

Ray Diagrams for Lenses

• Convex Lenses: Real and inverted images except when object is between F and O, resulting in virtual and erect image.
• Concave Lenses: Always form virtual, diminished, and erect images.

Sign Convention for Lenses

• Similar to mirrors, but measurements are from the optical center.

Lens Formula

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

Power of a Lens

• Definition: Measure of the lens's ability to bend light.
• Formula: ( P = \frac{1}{f} )
• Positive for converging lenses and negative for diverging lenses.