Light Rays

• Light travels in straight lines in a uniform medium (e.g., air, vacuum).
• A ray of light is represented by a straight line with an arrow showing the direction of light propagation.
• Rays are used in diagrams to represent how light travels, reflects, or refracts.
• Types of rays include:
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  • Incident ray: The incoming ray that strikes a surface.
  • Reflected ray: The ray that bounces off a reflective surface.
  • Refracted ray: The ray that bends when passing into a different medium.
  • Emergent ray: The ray leaving after passing through a medium.
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• Light rays are often used to locate images in mirrors and lenses using ray diagrams.

Ray Diagrams

• Ray diagrams are graphical methods to show the path of light rays as they interact with optical elements.
• They help in predicting image position, size, orientation, and nature (real or virtual).
• Common applications:

Plane Mirrors

A plane mirror is a flat reflecting surface.

• The image formed is:
  • Virtual (cannot be formed on a screen)
  • Same size as the object
  • Laterally inverted (left appears right, right appears left)
  • Same distance behind the mirror as the object is in front

Concave Mirrors

A concave mirror is a spherical mirror with its reflecting surface curved inward.

• It can form real or virtual images depending on the object’s position.
• Important positions:
  • Object beyond center of curvature (\(C\)): Real, inverted, diminished image between \(C\) and focus (\(F\)).
  • Object at \(C\): Real, inverted, same size at \(C\).
  • Object between \(C\) and \(F\): Real, inverted, magnified image beyond \(C\).
  • Object at \(F\): Image at infinity (no clear image).
  • Object between \(F\) and mirror: Virtual, upright, magnified image behind the mirror.

Mirror formula: \(\dfrac{1}{f} = \dfrac{1}{u} + \dfrac{1}{v}\)

• \(f\) = focal length
• \(u\) = object distance
• \(v\) = image distance

Convex Mirrors

A convex mirror is a spherical mirror with its reflecting surface curved outward.

• • It always forms:
    • Virtual image
    • Upright image
    • Diminished image
    • Located behind the mirror
  • Uses: Vehicle rear-view mirrors (give a wider field of view).

Sign Convention:

Rules for Drawing Ray Diagrams (Lenses/Mirrors)

• For converging lenses:
  
  • A ray parallel to the principal axis passes through the focal point after refraction.
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  • A ray passing through the center of the lens continues in a straight line.
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  • A ray through the focal point emerges parallel to the axis.
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• For concave/convex mirrors:
  
  • Use the same rules with reflection instead of refraction.
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