反射与折射

Refractive index (n) is a characteristic of a medium defined as the ratio of the speed of light in vacuum to the speed of light in that medium. Since air has a lower refractive index than water, light travels more slowly through water. This difference in refractive index between two media causes light to bend when transitioning between them, a phenomenon called refraction.

Snell's Law provides a mathematical relationship between the angle of incidence, angle of refraction, and the refractive indices of two media. The angle of incidence is measured between the incident light and the normal to the interface in the first medium, while the angle of refraction is measured in the second medium. This law allows calculation of how light bends when traveling between materials with different refractive indices.

The critical angle is the specific angle of incidence at which the refracted light travels along the interface, making the angle of refraction equal to 90 degrees. This occurs only when light travels from a denser medium to a less dense one. When the angle of incidence exceeds the critical angle, total internal reflection occurs, and light is completely reflected back into the first medium instead of refracting.

Real images form when light rays physically converge after passing through a lens, and can be captured on a screen, as in cameras or microscopes. Virtual images form when light rays appear to diverge, and the eye constructs a point of origin behind the lens; they cannot be projected onto a screen. The Thin Lens Equation determines image type: positive calculated distance indicates a real image, while negative distance indicates a virtual image.

Convex lenses can form both real and virtual images depending on object distance relative to focal length. When object distance exceeds focal length, a real image forms; when less than focal length, a magnified virtual image forms. Concave lenses always cause light rays to diverge, producing only demagnified virtual images regardless of object position. Both lens types use refraction to bend light and create images.

Optical fibers transmit data as light pulses through a core surrounded by cladding and protective coating. The cladding guides light along the core using total internal reflection, which keeps light signals contained within the fiber over long distances. This property enables fiber optic cameras used by doctors to view confined spaces in the human body and supports telecommunications applications like telephone signal transmission.

Optical microscopy uses visible light that is refracted through or reflected from a sample, then passes through single or multiple lenses to magnify the view. Refraction bends light to focus it on the sample, while reflection captures light from the sample surface. The combination of these optical phenomena through lenses allows visualization of objects too small for the naked eye, with images detected directly by the eye or captured digitally.