Light – Reflection and Refraction

Light – Reflection and Refraction

Light is essential for vision; we see objects because they reflect or transmit light to our eyes. In a dark room, objects are not visible due to the absence of light. During the day, sunlight enables us to see objects as it falls on them and is reflected. Transparent media allow light to pass through, enabling us to see objects behind them. Light exhibits several phenomena such as image formation by mirrors, twinkling of stars, rainbow colors, and bending by media. Observations show that light generally travels in straight lines, which is evident from the sharp shadows cast by opaque objects. This straight-line path of light is represented by rays. However, when light encounters very small obstacles, it bends around them, a phenomenon called diffraction, which cannot be explained by the ray model and requires wave theory. In the early 20th century, it was found that light also behaves like particles, leading to the modern quantum theory reconciling wave and particle nature. In this chapter, the focus is on reflection and refraction of light using the ray model, which helps explain many natural optical phenomena. The chapter further explores reflection by spherical mirrors and refraction through lenses and other media, with applications in daily life.

• Light enables vision by reflection or transmission to the eyes.
• Light travels in straight lines, represented by rays.
• Diffraction occurs when light bends around very small obstacles.
• Light exhibits both wave and particle nature (quantum theory).
• Reflection and refraction are fundamental optical phenomena.
• Spherical mirrors and lenses are practical applications of light behavior.
• 📌 Light ray: A straight line representing the path of light.
• 📌 Reflection: Bouncing back of light from a surface.
• 📌 Refraction: Bending of light when passing from one medium to another.

9.1 REFLECTION OF LIGHT

Reflection of light occurs when light rays strike a surface and bounce back. A highly polished surface like a mirror reflects most of the incident light. The laws of reflection are fundamental and apply to all reflecting surfaces including curved ones. These laws are: (i) The angle of incidence equals the angle of reflection, and (ii) The incident ray, the normal at the point of incidence, and the reflected ray all lie in the same plane. Plane mirrors form virtual, erect images that are laterally inverted, with image size equal to the object size, and the image appears as far behind the mirror as the object is in front. Curved surfaces like the shiny side of a spoon can act as curved mirrors, which can be concave (curved inward) or convex (curved outward). The image characteristics for curved mirrors differ from plane mirrors. Activities such as observing your face in a spoon's curved surface help understand image formation by curved mirrors.

• Reflection follows two fundamental laws applicable to all surfaces.
• Plane mirrors form virtual, erect, laterally inverted images of same size.
• Curved surfaces can act as spherical mirrors (concave or convex).
• Image properties vary with the curvature of the mirror.
• Reflection is the basis of vision and many optical devices.
• 📌 Angle of incidence: Angle between incident ray and normal.
• 📌 Angle of reflection: Angle between reflected ray and normal.
• 📌 Virtual image: Image formed where rays appear to diverge but do not actually meet.