Geometric Optics

Understanding reflection, refraction, and how light travels in straight lines

Topics

How do lenses work?

Lenses work by refracting (bending) light as it passes through. Convex lenses converge light rays to a focus point, while concave lenses diverge them. This bending occurs because light slows down when entering the lens material.

How does a camera work?

A camera works by using a lens to focus light onto a light-sensitive sensor or film. The lens creates an image, and the sensor/film captures it. A shutter controls how long light enters, and an aperture controls how much light enters.

How does a microscope work?

Microscopes work by using multiple lenses to magnify tiny objects. An objective lens near the specimen creates a magnified real image, which is then further magnified by an eyepiece lens for viewing. The combination of lenses provides high magnification, making microscopic details visible.

How does a telescope work?

Telescopes work by collecting and focusing light from distant objects using lenses or mirrors. They gather more light than the human eye and magnify images, making distant objects appear larger and brighter. Refracting telescopes use lenses, while reflecting telescopes use mirrors.

What is refraction?

Refraction is the bending of light as it passes from one medium to another with a different density. This occurs because light travels at different speeds in different materials, causing the light ray to change direction at the boundary between materials.

What is total internal reflection?

Total internal reflection occurs when light traveling from a denser medium (like water or glass) hits the boundary with a less dense medium (like air) at an angle greater than the critical angle. Instead of refracting, all light reflects back into the denser medium, creating perfect reflection.

Why do mirrors reflect?

Mirrors reflect because they have smooth, polished surfaces that bounce light back. When light hits a mirror, it reflects at the same angle it arrived (angle of incidence equals angle of reflection), creating a clear reflection.

Why do objects appear bent in water?

Objects appear bent in water because of refraction—light rays from underwater objects bend when they exit water into air, changing direction at the water-air boundary. Our eyes see the light rays as if they came from a different position, making objects appear displaced or bent.

Why do we see rainbows?

We see rainbows when sunlight is refracted (bent) and reflected inside water droplets. Different colors bend at different angles due to their wavelengths, separating white light into the spectrum of colors we see as a rainbow.

Why is the sky blue?

The sky is blue because of Rayleigh scattering—sunlight is scattered by tiny particles in the atmosphere, and blue light scatters more than other colors because it has shorter wavelength. This scattered blue light reaches our eyes from all directions, making the sky appear blue.