Light can bounce off surfaces {reflection, light}|, as surface molecules absorb and re-emit light. Reflections are like elastic collisions. Plane mirrors and wave tanks show reflections.
wavefront
Wavefronts are moving space disturbances. Behind wavefronts, all wavelets cancel each other, because wavelets have random phases. Beyond wavefronts, nothing has reached yet. Wavefronts are moving edges. Wavefront oscillation and movement carry energy. At surfaces, wavefronts re-radiate.
angles
Reflection angle equals incidence angle. Because light travels straight, light has no sideways motion components, and light plane stays the same. Angles are the same, because light effects are symmetric.
images
Images from flat mirrors appear to be behind mirror and so are virtual images. Images appear at same distance from mirror as distance that objects are from mirror. Images have same size and orientation as objects. Reflections from flat surfaces only reverse right and left.
surfaces
Dielectrics can be mirrors.
polarization
At incidence angle 45 degrees, if reflection from plane mirror has 90-degree angle between reflected and refracted beams, light polarizes.
In reflection, incident light hits surface at angle {angle of incidence}| {incidence angle} to perpendicular.
In reflection, reflected light leaves surface at angle {reflection angle} {angle of reflection}| to perpendicular, as superposed wavelets add to make wavefront. Reflection angle equals incidence angle and is in same plane.
Curved mirrors {curved mirror} focus incoming parallel light rays onto point {focus, mirror}.
types
Curved mirrors {spherical mirror} can have constant radius. Spherical mirrors {convex mirror} can curve out. Curvature radius is positive if curve is convex. For convex mirrors, image is always virtual and erect. For convex mirrors, if object is inside focal point, image is bigger. For convex mirrors, if object is outside focal point, image is smaller.
Spherical mirrors {concave mirror} can curve in. Curvature radius is negative if curve is concave. For concave mirrors, if object is outside focal point, image is real and inverted. For concave mirrors, if object is inside focal point, image is virtual, erect, and bigger.
Curved mirrors {parabolic mirror} can have changing radius.
magnification
Ratio of image size I to object size O equals ratio of distance q of image from mirror to distance p of object from mirror: I/O = q/p.
focal length
Focal length F is spherical-mirror curvature radius R divided by two: F = R/2.
Image distance I and object distance O relate to focal point distance F {lens equation, mirror}: 1/F = 1/I + 1/O.
Find object image using incoming straight lines from object and outgoing straight lines to image {method of rays} {rays method}, which reflect from spherical mirror points.
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Date Modified: 2022.0225