review

ELECTROMAGNETIC WAVES

  • these are continuous range of electromagnetic waves arranged in order of frequency or wavelength. it is produced by accelerating changes.

frequency

  • number of waves that pass a fixed point in unit time. it is measured by hertz.

wavelength

distance over which a wave’s shape repeats

radiowaves

  • longest of all electromagnetic waves. it has the largest wavelength and the lowest frequency.

  • discovered by heinrich hertz in 1887

  • divided into specific bands for wireless communications

  • sources: sun & jupiter

  • radar: acronym for radio detection and ranging.

examples of radiowaves:

  • radio broadcasting

  • televisions

  • mri and ct scans

microwaves

  • mainly used for communication due to high frequency radio waves and smaller wavelengths

  • discovered by james clerk maxwell in 1864

  • commonly used in the medical field

examples of microwaves:

  • treatment of breast cancer via microwave tomography

  • wifi or internet

  • kitchen appliances

  • air-traffic control

infrared waves (infrared radiation - IR)

  • commonly used for short-range communication in wireless keyboards, mice, printers, and remote controls due to their relatively lower energy which limits their range.

  • below red; discovered by william herschel in 1800

  • can be felt as heat. shorter wavelength, higher frequencies

examples of infrared waves:

  • night-vision cameras

  • thermometers

  • remote controls of television sets

  • heat scanner

visible light

  • discovered by isaac newton when he refracted white light with a prism

  • sequence of colors: longest to shortest (ROYGBIV)

  • helps in making objects visible to the eye

  • makes spectrum of colors visible to the eye

examples of visible light:

  • laser (light amplification)

  • traffic lights

  • commercial displays

  • car headlights

uv rays (ultraviolet radiation)

  • discovered by johann wilhem ritter

  • has 3 types: uva, uvb, uvc

  • major source is the sun

  • uva: accounts for 95% of the solar uv reaching earth, penetrates the dermis

  • uvb: filtered by the ozone in the atmosphere, affects epidermis

  • uvc: is absorbed by the atmosphere, it does not reach earth

examples of uv rays:

  • black light

  • production of vitamin d in the body

  • forensic investigation

  • sun burn

x-ray (roentgen ray)

  • discovered by conrad roentgen

  • x means unknown quantity; unknown origin and nature

  • soft x-rays have lower energy: can penetrate flesh and bones

  • hard x-rays have higher energy: more penetrating, used in industries

  • sources: sun and stars

examples of x-ray:

  • port baggage scanners

  • bone fracture scanners

  • chest scan

  • taking photographs of internal body parts

gamma rays

  • given off by radioactive elements such as cobalt and cesium

  • sources: sun, interstellar clouds, remnants of supernova

  • discovered by paul villard; 1900

  • has the smallest wavelength and highest frequency

examples of gamma rays:

  • detect cracks in metals

  • sterilizing equipment

  • radiotherapy: destroy cancer cells

OPTICS: REFLECTION AND MIRRORS

  • branch of physics, studies behavior and properties of light as well as its interactions with matter.

visible light

  • form and part of the electromagnetic spectrum; the only thing we see.

  • can be reflected, absorbed, refratced

  • c = speed of light; in a constant vaccum (empty)

  • c = 3.0 Ă— 10^8 m/s

reflection

  • change in the direction of the propagation of a wave when the wave strikes the surface of a different material

  • bouncing back of light

law of reflection

  • the angle of incidence (incoming ray) equals the angle of reflection (outgoing ray)

  • it works for flat, plane surfaces only

  • angles are measured from a perpendicular line to the surface called a normal

descriptions of images (LOST)

location: in front of the mirror (outside), at the back of the mirror (inside)

orientation: upright or inverted

size/magnification: reduced, enlarged, same size

type: real images: (ones you can project on to a screen, for mirrors: same side)

or virtual image: (images which cannot be visually projected on a screen, always on the opposite)

2 types of spherical mirrors: concave and convex mirrors

concave mirrors: (converging)

  • one that is spherical in nature by which it can focus parallel light rays to a point directly in front of its surface.

  • curves inward in the direction of the incident rays

  • can form real or virtual images

convex mirrors: (diverging)

  • bulges outward to the incident rays.

  • always produces virtual, upright, and smaller than object

spherical mirror parts:

are mirrors cut out from a spherical reflecting surface.

center of curvature C: center of the sphere from where the mirror was taken

vertex V: center of the mirror, called the pole of the mirror

radius of curvature R: is the radius of the sphere. it is the distance between C and V

principal axis or optical axis: the straight line joining C and V

aperture: width of the mirror

principal focus F: the point where reflected rays meet as in the case of a converging mirror

focal length F: the distance from the vertex to the principal focus

refraction of light

  • change in the direction of light when it passes from one medium to another of different optical density ( transparency of a substance to light )

  • bending of light

spherical lenses

  • a piece of glass or transparent material that has at least one spherical surface, may be concave or convex

concave lens: diverging

  • thicker at the edges than at the middle

  • used to correct nearsightedness

  • may be double concave, plano-concave, convexo-concave

  • always virtual, upright, smaller, same side of lens

convex lens: converging

  • thicker at the middle than at the edges

  • used to correct farsightedness

  • may be double convex, plano-convex, concavo-convex

  • image depends on the distance of the object from the lens

myopia

  • nearsightedness

  • it is because the eyeball is longer than the normal or is too curved

  • corrected by concave lens because it causes the light to bend slightly

hyperopia

  • farsightedness

  • it is because the eyeball is too short and image of a close object is formed behind the retina

  • can be corrected by a convex lens

optical instruments:

projector: an optical device that projects an image onto a surface, commonly a projection screen

magnifier: a device used for magnification

microscope: an instrument used to magnify small objects

telescope: to view objects from afar

camera

  • shutter allows light to reach the film of photo cells

  • diaphragm consists of overlapping blades that open and close to adjust the size of aperture

  • aperture is along with the speed of shutter to control the amount of light that reaches the film or photo cells

eye: organs of the visual system