Physics Chapter on Light

Introduction to Light

• Light is energy that allows visibility; it originates from a source and interacts with objects.
• Electromagnetic waves travel at the speed of light, which is approximately 3.0 × 10^8 m/s.

Nature of Light

• Exhibits properties of rays (reflection), waves (interference, diffraction), and particles (photoelectric effect).
• Wave-particle duality explains light's behavior depending on the situation.

Laws of Reflection

• When light hits a surface, it can be absorbed, reflected, or refracted.
• Laws of reflection state that the incident ray, reflected ray, and normal lie in the same plane, and the angle of incidence equals the angle of reflection (∠i = ∠r).

Propagation of Light

• Light travels in straight lines (rectilinear propagation).
• Fermat’s Principle states that light takes the quickest path, which is not always the shortest.

Applications of Fermat’s Principle

• In a uniform medium, light travels in straight lines, supporting the law of reflection.
• The mirage effect illustrates light's bending and varying speed in different temperatures.

Plane Mirror

• A flat, polished surface reflects light, producing virtual and erect images located equidistantly from the mirror.
• Images can be classified as real or virtual, erect or inverted, magnified or diminished.

Principle of Reversibility of Light

• Light rays retrace their paths when their direction is reversed after reflection.

Spherical Mirrors

• Spherical mirrors are made from concave or convex shapes, reflecting light differently.
• The focal length (F) is half the radius of curvature (R); F = R/2.

Characteristics of Spherical Mirrors

• Key terms include pole (P), center of curvature (C), radius of curvature (r), and principal axis.
• Ray diagrams aid in understanding image formation under various conditions.

Mirror Formula

• The mirror formula relates object distance (u), image distance (v), and focal length (f): 1/v + 1/u = 1/f.

Refraction and Refractive Index

• Refraction occurs when light passes from one medium to another, bending based on the media's refractive indices.
• The relative refractive index is calculated as n = c/v, where c is the speed of light in vacuum, and v is the speed in the medium.

Total Internal Reflection

• Occurs when light travels from denser to rarer mediums; critical angle must be exceeded for reflection instead of refraction.
• Example applications include optical fibers and mirages.

Spherical Lenses

• Made by binding two spherical surfaces; convex lenses converge light, while concave lenses diverge it.
• Important terms include optical center (P), principal axis, focus (F), and focal length.

Lens Formula and Power

• Lens formula is 1/v = 1/u = 1/f, illustrating the relationships between object distance, image distance, and focal length.
• Power of a lens is defined as 1/f (in meters), measured in diopters (D).

Applications of Lenses

• Spherical lenses are utilized in spectacles, binoculars, magnifying glasses, and telescopes.

Sample Problems

• The refractive index of diamond with respect to carbon disulfide calculated as 1.48.
• Focal length of a mirror with an object 20 cm from it, yielding an image 15 cm behind, calculated as 60 cm.
• Image height from a concave lens with a 3 cm high object placed 80 cm away, resulting in a 0.6 cm tall image.