Light Chapter - Key Concepts and Formulas

Introduction

• Focus: Covering all physics formulas and concepts in 15 minutes.
• Full course video links provided in the card section and description.
• Objective: Understand the key points to handle exam questions effectively.

Reflection

Types of Reflection

• Smooth Surface Reflection: Incident rays fall parallel and reflect parallelly.
• Rough Surface Reflection: Does not follow typical reflection laws.

Key Definitions

• Incident Ray: The ray of light that falls on the surface.
• Reflected Ray: The ray of light that bounces off the surface.
• Normal: The perpendicular line at the point of incidence.
• Angle of Incidence: Angle between the incident ray and the normal.
• Angle of Reflection: Angle between the reflected ray and the normal.

Properties of Image Formed by Plane Mirror

• Image size = Object size
• Image distance from mirror = Object distance from mirror
• Image is always erect and virtual (forms behind the mirror).

Spherical Mirrors

Types of Spherical Mirrors

• Concave Mirror: Reflecting surface curved inward (converging mirror, forms real focus).
• Convex Mirror: Reflecting surface curved outward (diverging mirror, forms virtual focus).

Key Components of Spherical Mirrors

• Center of Curvature: Center of the sphere from which the mirror is a part.
• Radius of Curvature: Radius of the sphere from which the mirror part is created.
• Principal Axis: Line passing through the center of curvature and the pole.
• Aperture: Reflecting surface area of the mirror.
• Focus: Point where parallel light rays converge (concave) or appear to diverge from (convex).

Standard Incident Rays for Concave and Convex Mirrors

• Parallel to principal axis => Passes through the focus.
• Through the focus => Becomes parallel to the principal axis.
• Through the center of curvature => Reflects back on the same path.

Ray Diagrams: Concave Mirror

• Object at Infinity: Image at focus (Real, Inverted, Highly diminished)
• Object Beyond Center of Curvature: Image between C and F (Real, Inverted, Diminished)
• Object at Center of Curvature: Image at center of curvature (Real, Inverted, Same size)
• Object between C and F: Image beyond C (Real, Inverted, Enlarged)
• Object at Focus: Image at infinity (Real, Inverted, Highly enlarged)
• Object between F and Pole: Image behind mirror (Virtual, Erect, Enlarged)

Ray Diagrams: Convex Mirror

• Object at Any Position: Image between focus and pole (Virtual, Erect, Diminished)

Mirror Formula and Magnification

• Mirror formula: 1/f = 1/v + 1/u
• Magnification (m):
  • m = height of image / height of object
  • m = -v/u

Sign Convention

• Positive Values: Measurements in front of the mirror (in case of mirrors).
• Negative Values: Measurements behind the mirror.
• Shortcut (PANTH): Positive when away from the object, Negative when towards the object.

Refraction

What is Refraction?

• Bending of light when it passes from one medium to another having different optical densities.

Laws of Refraction

• Incident ray, normal, and refracted ray lie on the same plane.
• Ratio of sine of angle of incidence to the sine of angle of refraction constant (Refractive Index).

Refractive Index

• Indicates how much light bends when it enters a medium.
• Absolute Refractive Index: n = c/v (Speed of light in vacuum / Speed in medium)
• Comparative Refractive Indices: n1/n2 = c1/v1 / c2/v2

Spherical Lenses

Types of Spherical Lenses

• Convex Lens: Thicker at center, thinner at edges (Converging lens).
• Concave Lens: Thinner at center, thicker at edges (Diverging lens).

Key Components of Spherical Lenses

• Center of Curvature: Center of the spheres from which the lenses are made.
• Radius of Curvature: Distance between the center of curvature and the lens surface.
• Optical Center: Center of the lens.
• Principal Axis: Line passing through the optical center and centers of curvature.
• Aperture: Refracting surface area of the lens.

Focus points in Lenses

• Convex Lens: Converging light rays meet at real focus.
• Concave Lens: Diverging light rays appear to originate from a virtual focus.

Ray Diagrams: Convex Lens

• Object at Infinity: Image at focus (Real, Inverted, Highly diminished)
• Object Beyond 2F: Image between F and 2F (Real, Inverted, Diminished)
• Object at 2F: Image at 2F (Real, Inverted, Same size)
• Object between F and 2F: Image beyond 2F (Real, Inverted, Enlarged)
• Object at F: Image at infinity (Real, Inverted, Highly enlarged)
• Object between F and Optical Center: Image on same side of lens (Virtual, Erect, Enlarged)

Ray Diagrams: Concave Lens

• Object at Any Position: Image between F and Optical Center (Virtual, Erect, Diminished)

Lens Formula and Magnification

• Lens formula: 1/f = 1/v - 1/u
• Magnification (m):
  • m = height of image / height of object
  • m = v/u

Power of a Lens

• Power (P): P = 1/f (Reciprocal of focal length in meters, measured in diopters)

Important Concepts

• Accurate conversions to meters for focal lengths.
• Consistency in sign conventions (similar to mirror problems).