Light Reflection and Refraction

Introduction

• Light is a form of energy traveling in a straight line.
• Reflection: Light bounces back from a smooth, polished surface.
• Refraction: Light changes direction when passing from one medium to another.

Reflection of Light

Mirrors

• Mirror: An opaque object with a shiny, reflective surface.
• Plain mirrors create virtual images:
  • Virtual Images: Appear behind the mirror, same distance as the object.
  • Size: Same as the object, no magnification.
  • Laterally Reversed: Left and right are swapped.

Spherical Mirrors

• Types: Convex (outward curve) and Concave (inward curve).
• Key Terms:
  • Pole (P): Center point of the mirror's 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 P and C.
  • Principal Focus (F): Point where parallel rays converge (concave) or appear to diverge (convex).
  • Focal Length (f): Distance between P and F.

Image Formation by Concave Mirror

• Various object positions (e.g. at infinity, beyond C) result in different image properties (e.g. highly diminished, same size, enlarged).
• Uses: Shaving mirrors, dentist mirrors, torch reflectors.

Image Formation by Convex Mirror

• Typically, only two object positions considered:
  • At infinity: Image at focus behind the mirror, virtual.
  • Between infinity and P: Image between P and F, virtual.
• Use: Rear view mirrors in vehicles.

Sign Convention for Spherical Mirrors

• Object always placed to the left of the mirror.
• Distances measured from the mirror's pole.
• Directions of measurement define positive and negative values.

Mirror Formula and Magnification

• Mirror Formula: (\frac{1}{V} + \frac{1}{U} = \frac{1}{F})
  • V = image distance, U = object distance, F = focal length.
• Magnification (M): Ratio of image height ((h')) to object height ((h)) and can also be calculated using distances: (M = \frac{-V}{U})

Refraction of Light

• Refraction: Change in direction when light passes from one medium to another due to speed change.
• Examples: A straw in water appearing bent.

Laws of Refraction

• Incident ray, refracted ray, and normal lie in the same plane.
• (\frac{\sin i}{\sin r} = \text{constant}) (Snell's Law).
• Refractive index (n): Measure of light speed reduction, (n = \frac{c}{v}) where c is the speed in vacuum and v in the medium.

Refraction by Spherical Lenses

• Types: Convex (converging) and concave (diverging).
• Key Terms:
  • Optical Center (O): Central point of the lens.
  • Principal Focus (F): Point where parallel rays converge or appear to diverge after passing through the lens.
  • Focal Length (f): Distance from O to F.

Image Formation by Convex Lens

• Various object positions (e.g. at infinity, beyond 2F1) result in different image properties (e.g. highly diminished, same size, enlarged).

Image Formation by Concave Lens

• Typically, two object positions considered:
  • At infinity: Image at focus F1, virtual.
  • Between infinity and O: Image between F and O, virtual.

Lens Formula and Magnification

• Lens Formula: (\frac{1}{V} - \frac{1}{U} = \frac{1}{F})
• Magnification (M): (M = \frac{h'}{h} = \frac{V}{U})

Power of Lens

• Power (P): (P = \frac{1}{F}) measured in diopters (D).
• Convex lens: Positive power, diverging lens: Negative power.