light

• Law of Reflection: A ray is a mathematical line drawn perpendicular to the wavefronts of a lightwave. It shows the direction of propagation of electromagnetic energy. In specular (or mirror) reflection, the angle of incidence (θi) equals the angle of reflection (θr), as shown in Fig. 36-1. Furthermore, the incident ray, reflected ray, and normal to the surface all lie in the same plane, called the plane-of-incidence.
• Concave mirrors form inverted real images of objects placed beyond the principal focus. If the object is between the principal focus and the mirror, the image is virtual, erect, and enlarged.
• Convex mirrors produce only erect virtual images of objects placed in front of them. The images are diminished (smaller than the object) in size.
• Mirror Equation for both concave and convex spherical mirrors:

  
• SIGN CONVENTION

  • s0 is positive when the object is in front (i.e., to the left) of the mirror. • si is positive when the image is real (i.e., in front or to the left of the

  mirror).• si is negative when the image is virtual (i.e., behind or to the right of

  the mirror).• f is positive for a concave mirror and negative for a convex mirror.• R is positive when C is to the right of the mirror (i.e., when the mirror

  is convex).• R is negative when C is to the left of the mirror (i.e, when the mirror

  is concave).
• The Size of the Image formed by a spherical mirror is given by

  
• The Speed of Light (c) as ordinarily measured varies from material to material. Light (treated macroscopically) travels fastest in vacuum, where its speed is c = 2.998 × 108 m/s. Its speed in air is c/1.000 3. In water its speed is c/1.33, and in ordinary glass it is about c/1.5.
• Index of Refraction (n): The absolute index of refraction of a material is defined as

  
• Refraction: When a ray of light is transmitted obliquely through the boundary between two materials of unlike index of refraction, the ray bends. This phenomenon, called refraction
• Total Internal Reflection: A ray of light traveling within a denser medium strikes the surface separating this medium from a less dense medium at an angle greater than the critical angle. At such an angle, all the light is reflected back into the denser medium without any being transmitted across the interface.
• Snell’s Law: If n1 is the index of refraction of one medium and n2 that of another, then the ratio of the sines of the angles of incidence and refraction is equal to the ratio of the indices of refraction of the media; that is, sin i /sin r = n1 /n2.
• Dispersion: Different colors are bent differently by a prism because they have different wavelengths and therefore different speeds in the prism material. Thus, white light entering a prism is dispersed into a spectrum of colors on leaving the prism.
• refractive index

  
• converging, or positive, lenses are thicker at the center than at the rim and will converge a beam of parallel light to a real focus.
• Diverging, or negative, lenses are thinner at the center than at the rim and will diverge a beam of parallel light from a virtual focus.
• The principal focus (or focal point) of a thin lens with spherical surfaces is the point F where rays parallel to and near the central or optical axis are brought to a focus; this focus is real for a converging lens and virtual for a diverging lens.
• The focal length ƒ is the axial distance of the principal focus from the lens.
• types of lenses

  
• Lensmaker’s Equation:

  
• Lens Power in diopters (m-1) is equal to 1/f, where f is the focal length expressed in meters.