Reflection of Light

• Plane (flat) mirrors produce a reflection.
• Rays from an object reflect off the mirror into our eyes, but we see them behind the mirror.
• The image has these properties:
  • The image is the same size as the object.
  • The image is the same distance from the mirror as the object.
  • A line joining equivalent to the points of the image and object meet the mirror at a right angle.
  • The image is virtual; no rays pass through the image and the image cannot be formed on a screen
  • Laws of Reflection: Angle of incidence = Angle of reflection
    • The incident ray, reflected ray and normal are always on the same place (side of the mirror)

Refraction of Light

• Refraction is the bending of light when light travels from one medium to another.

Experimental Demonstration

• Using the ray box, pass a ray through a glass slab on a white sheet of paper.
• Mark two points on the incident ray, refracted ray, emergent ray, and draw an outline of the glass slab with a pencil on the paper.
• Then, by connecting the dots, you can produce a diagram like the one below, a protractor is used to find the angles.
• When a ray passes through a transparent parallel-sided material, its passage will look like this:
  
• NOTE: The emergent ray is parallel to the incident ray.

Critical Angle

• The angle at which the refracted ray is parallel to the surface of the material.
• If the angle of incidence is greater than the critical angle, there is no refracted ray, there is total internal reflection.
• If the angle of incidence is less than the critical angle, the incident ray will split into a refracted ray and a weaker reflected ray.
  
• Refractive Index, n = ^{Speed of light in vacuum}/_{Speed of light in a medium}
• Refractive index = ^{sin i}/_{sin r}
• Critical angle = sin^{-1 1}/_n

Optical Fibers

• Light put in at one end is totally internally reflected until it comes out the other end.
• It is used in communications: Signals are coded and sent along the fiber as pulses of laser light.
• It is used in medicine:  An endoscope, an instrument used by surgeons to look inside the body, contains a long bundle of optic fibers.

Thin Converging Lens

• Principal Focus is the point where rays parallel to the principal axis converge with a converging lens.
• Focal Length is the distance from the principal focus and the optical center.
• Principal Axis is the line that goes through the optical center, and the two foci.
• Optical Center is the center of the lens.
• A Real Image can be caught on a screen.
• A Virtual Image cannot be caught on a screen.

Real Image

• When the object is further away from the optical center than F‘ is
  
  1. A ray through the center of the lens passes straight through the lens.
  2. A ray parallel to the principal axis passes through the focus on the other side of the lens
  3. A ray through F’ will leave the lens parallel to the principal axis.

Virtual Image

• When the object is closer to the optical center than F‘ is
  

• • Magnifying Glass
    • When a convex lens is used like this – an object is closer to a convex (converging) lens than the principal focus (like the diagram above), the rays never converge. Instead, the appear to come from a position behind the lens.
    • The image is upright, and magnified, it is a virtual image.

Dispersion of Light

• Refraction by a Prism
  • When light is refracted by a prism, the incidence ray is not parallel to the emergent ray, since the prism’s sides are not parallel.
  • If a beam of white light is passed through a prism, it is dispersed into a spectrum.
  • White light is a mixture of colors, and the prism refracts each color by a different amount – red is deviated least and violet most.

Light Spectrum

Electromagnetic Spectrum

• All electromagnetic waves:
  • travel at the speed of light; 3 × 10⁸ m/s
  • don’t need a medium to travel through (they travel through a vacuum)
  • can transfer energy
  • are produced by particles oscillating or losing energy in some way
  • are transverse waves

Uses

• Radio Waves: In radio and television communications
• Microwaves: Satellite television and telephones
  • Safety Issue: They cause internal heating of body tissues
• Infrared: Electrical appliances (radiant heaters and grills), remote controllers for televisions and intruder alarms
• X-rays: Medicine (x-ray photography and killing cancerous cells) and security
  • Safety Issue: It is a mutagen, it can cause cancer (mutations)
• Monochromatic: Light of a single wavelength and color (used in lasers)