In the field of physics, geometric optics is the study of light as it propagates in straight lines, also known as rays. It focuses on understanding the behavior of light when interacting with various optical elements such as mirrors and lenses. Geometric optics simplifies the complexities of wave properties of light and provides a practical approach to analyzing light propagation.

Geometric optics is based on a few fundamental principles. The principle of rectilinear propagation states that light travels in straight lines in a homogeneous medium unless it encounters an obstacle or is refracted or reflected. For instance, when light passes through a transparent medium like air, it refracts or bends slightly due to variations in the medium's density.

A prominent concept in geometric optics is reflection. The law of reflection states that when light strikes a smooth surface, the angle of incidence is equal to the angle of reflection. This principle enables us to predict the path of reflected light in mirrors and other reflective surfaces.

Additionally, refraction plays a crucial role in geometric optics. Refraction occurs when light crosses the boundary between two transparent materials with different refractive indices. Snell's law, which governs refraction, states that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is equal to the ratio of the velocities of light in the two media.

By understanding the principles of geometric optics, we can analyze and predict how light will behave when interacting with various optical devices, allowing us to design and optimize the performance of optical systems.