Light and optics

Light Rays

Light rays are imaginary lines that show the direction in which light travels. They help us understand how light moves, reflects, and bends when it hits different surfaces or passes through lenses.

Reflection of Light

Reflection of light is when light bounces off a surface. For example, when you look in a mirror, the light from your face reflects off the mirror and into your eyes, allowing you to see your reflection. The law of reflection states that the angle of incidence (the angle at which light hits the surface) is equal to the angle of reflection (the angle at which it bounces off).

Plane Mirrors

Plane mirrors are flat mirrors that produce a virtual image of an object. The image appears to be behind the mirror and is the same size as the object. They are commonly used in everyday life, like in bathroom mirrors. The image formed by a plane mirror is always upright and laterally inverted.

Curved Mirrors

Curved mirrors are mirrors with a curved surface, and they can be concave or convex. Concave mirrors curve inward like a bowl, and they can focus light to a point, creating real or virtual images. Convex mirrors curve outward, like the outside of a sphere, and they diverge light rays, forming virtual, upright, and smaller images. They are often used in headlights, reflectors, and security mirrors.

Refraction of Light

Refraction of light is the bending of light as it passes from one medium to another with a different density. For example, when light passes from air into water, it slows down and bends, making objects under water appear closer to the surface than they actually are. The amount of bending depends on the change in speed of light in the different media and is described by Snell's law.

General Snell’s law

Snell's law describes how light bends when it passes from one medium to another. It states that the ratio of the sine of the angle of incidence (the angle between the incident ray and the normal) to the sine of the angle of refraction (the angle between the refracted ray and the normal) is constant and equal to the ratio of the speeds of light in the two media or equivalently, the inverse ratio of their refractive indices.

General Snell’s law - Mathematical

The mathematical expression for Snell's law is:

SIN(θ₁) / SIN(θ₂) = n₂ / n₁

Where:

- θ₁ = angle of incidence

- θ₂ = angle of refraction

- n₁ = refractive index of the first medium

- n₂ = refractive index of the second medium

This law helps us understand how light bends when passing through different materials.

Total Internal Reflection

Total internal reflection occurs when light tries to pass from a denser medium to a less dense medium at an angle greater than the critical angle. Instead of passing through, the light is completely reflected back into the denser medium. This phenomenon is used in optical fibers and prisms.

Lenses

Lenses are transparent objects that bend light to form images. They can be convex (converging) or concave (diverging). Convex lenses are thicker in the middle and focus light to a point, forming real or virtual images. Concave lenses are thinner in the middle and cause light rays to diverge, forming virtual images. Lenses are widely used in glasses, cameras, microscopes, and telescopes to magnify or focus images.