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.
- 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.
- 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
- 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.
- When the object is further away from the optical center than F‘ is
- A ray through the center of the lens passes straight through the lens.
- A ray parallel to the principal axis passes through the focus on the other side of the lens
- A ray through F’ will leave the lens parallel to the principal axis.
- 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.
- Magnifying Glass
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.
- 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
- 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)