Ray Optics: Reflection and Refraction

• Ray optics, also known as geometrical optics, describes light propagation in terms of rays.

Basic Principles

• Light travels in straight lines.
• Light rays change direction when they encounter a boundary between different media (reflection and refraction).
• Ray optics is an approximation that is valid when the wavelength of light is much smaller than the size of the objects it encounters.

Reflection

• Reflection is the change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated.
• Specular reflection is reflection from a smooth surface, like a mirror.
• Diffuse reflection is reflection from a rough surface.
• The law of reflection states that the angle of incidence is equal to the angle of reflection, and the reflected ray is in the same plane as the incident ray and the normal to the surface.

Refraction

• Refraction is the change in direction of a wave passing from one medium to another caused by its change in speed.
• The refractive index of a medium is the ratio of the speed of light in vacuum to the speed of light in the medium (n = c/v).
• Snell's law relates the angles of incidence and refraction to the refractive indices of the two media (n1sinθ1 = n2sinθ2).
• When light passes from a medium with a higher refractive index to one with a lower refractive index, the light bends away from the normal.
• When light passes from a medium with a lower refractive index to one with a higher refractive index, the light bends towards the normal.

Total Internal Reflection

• Total internal reflection occurs when light travels from a medium with a higher refractive index to a medium with a lower refractive index.
• If the angle of incidence is greater than the critical angle, the light is entirely reflected.
• The critical angle is the angle of incidence for which the angle of refraction is 90 degrees (sinθc = n2/n1, where n1 > n2).

Lenses

• A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction.
• Convex (converging) lenses are thicker in the middle and converge light rays.
• Concave (diverging) lenses are thinner in the middle and diverge light rays.
• The focal length (f) of a lens is the distance from the lens to the point where parallel rays converge (for convex lenses) or appear to diverge from (for concave lenses).
• The lensmaker's equation relates the focal length of a lens to its refractive index and the radii of curvature of its surfaces: 1/f = (n-1)(1/R1 - 1/R2).
• The thin lens equation relates the object distance (u), image distance (v), and focal length (f) of a lens: 1/f = 1/u + 1/v.
• Magnification (M) is the ratio of the image height to the object height: M = -v/u.

Optical Instruments

• The human eye is an optical instrument that uses a lens to focus light onto the retina.
• A camera uses a lens to focus light onto a sensor.
• A microscope uses multiple lenses to magnify small objects.
• A telescope uses lenses or mirrors to magnify distant objects.

Prisms

• A prism is a transparent optical element with flat, polished surfaces that refract light.
• Prisms can be used to disperse white light into its constituent colors.
• The angle of deviation is the angle between the incident ray and the emergent ray.

Explore ray optics, including the principles of light traveling in straight lines. Learn about reflection, including specular and diffuse reflection and refraction. Understand the law of reflection and how light changes direction when passing through different mediums.