science 30

• Radiation


  Energy emitted in the form of particles or waves
• Electromagnetic radiation (EMR)


  A wave of energy consisting of electric and magnetic fields travelling at right angles to one another (which is called a transverse wave)
• Humans can detect some EMR through their eyes as colours (visible light) and with the skin as heat (infrared radiation)
• EMR can travel through a complete vacuum (empty space)
• Cycle


  One complete vibration of a wave (either electric or magnetic field)
• Wavelength


  The distance required for one complete cycle. The symbol for wavelength is λ (lambda), measured in metres
• Frequency


  The number of cycles per second, measured in Hz (Hertz)
• Determining wavelength


  1. Determine the wavelength of this EMR

  2. Determine the wavelength of the following TWO EMR
• Electromagnetic spectrum


  The wide band of different types of EMR ranging from radio waves to gamma rays
• Radio waves


  • The lowest frequency of all types of electromagnetic radiation
  • Used primarily for communications
  • The inability of radio waves to penetrate metal objects means that an external antenna is often required
  • When a radio wave passes the antenna of a receiver, the vibrating electric fields within the wave cause electrons within the antenna to vibrate as well. The circuitry attached to the antenna decodes this electric signal, providing the user with the radio or TV broadcast
• Magnetic resonance imaging (MRI)


  • A method of obtaining internal images of objects such as soft tissues especially living organisms, by using radio waves and strong magnetic fields
• Microwaves


  • Higher frequency (and energy) than radio waves
  • Produced by high-frequency vibrations of electrons in electric circuits
  • Prolonged exposure on living tissue can be hazardous, especially to the lens of the eye (resulting in cataracts)
  • Used in communication because they can penetrate rain, snow, and haze
• Infrared radiation


  • Higher frequency (and energy) than microwaves
  • Emitted by the vibration of molecules (which occurs when a material is heated)
  • Humans and most animals sense infrared radiation through the skin
  • Used in TV and DVD remote controls
• Visible light


  • Higher frequency (and energy) than infrared radiation
  • Visible light that is reflected off objects and enters our eyes is the colour we perceive the object to be (Roy G Biv)
  • Emitted by hot objects

  
• Fiber optics


  • Transmission of light by optical fibers. They guide light around corners using reflection
  • Importance: Provides a method of internal illumination and examination through a natural orifice or through a very small artificial opening (endoscopy)
• Ultraviolet radiation


  • Higher frequency (and energy) than visible light
  • Emitted from sources that are very hot
  • Can do permanent damage to living tissue (skin cancer, DNA mutation) because UV is ionizing radiation (ejects electrons from atoms)
  • Earth's ozone blocks the most hazardous forms of UV radiation

  
• x-rays

  • Higher frequency (and energy) than UV rays
  • Can penetrate skin, fat, and muscle but are blocked by dense tissues like teeth and bones
  • Produced using high-voltage tubes when high-speed electrons collide with a metal target
  • Causes DNA mutation because x-rays are ionizing radiation, but can be used in radiation therapy to treat forms of cancer

  
• Gamma radiation


  • Gamma photons have the highest frequency of all types of electromagnetic radiation
  • Is produced by unstable nuclei of radioactive material
  • Gamma photons also have the highest energy and the greatest penetrating power
  • It is used to treat brain cancers
  • Emission tomography (PET and SPECT) is a nuclear medicine functional imaging technique that is used to observe metabolic processes in the body. Can be used track blood flow and soft tissue imaging

  
• Nuclear fusion


  The process where two smaller nuclei join to form a larger nucleus, releasing energy
• Solar flare


  A very powerful eruption in the Sun's atmosphere that is triggered by the realignment of the Sun's magnetic field lines
• Reflection


  • The bouncing off of waves from any surface they hit
• Polarization


  Confining a wave to vibrate in one direction

  
• Refraction


  • The change in direction of a wave as it travels from one medium to another
  • When light moves into a medium with a higher index of refraction it bends towards the normal
  • When light moves into a medium with a lower index of refraction it bends away from the normal
• The fact that each color or wavelength of light refracts differently is what causes white light to disperse into its spectrum of colors
• Angle of incidence


  The angle at which a ray of light or other radiation strikes a surface

  
• Angle of reflection


  The angle at which a ray of light or other radiation is reflected from a surface
• The angle of incidence is equal to the angle of reflection
• Reflection on a parabola

  • Incoming rays are parallel and become concentrated as they reflect off the surface and become focused
• Applications of parabolic reflection

  • Reflecting telescopes
  • Satellites
  • Parabolic microphones
• Terminology related to reflection

  • Reflected ray
  • Incident ray
  • Normal
  • Angle of incidence
  • Angle of reflection
• Polarization occurs as light reflects from horizontal surfaces
• Refraction


  The change in direction of a wave as it travels from one medium to another

  
• Refraction


  • When light moves into a medium with a higher index of refraction it bends towards the normal
  • When light moves into a medium with a lower index of refraction it bends away from the normal
• Red light bends the least and blue/violet light the most when passing through a prism
• The refraction of light when it passes from a fast medium to a slow medium bends the light ray toward the normal to the boundary between the two media
• Galileo's refracting telescope


  • Consisted of a convex lens at one end and a concave lens at the other
  • The quality of the glass was not good
  • Forced the light to enter the telescope through a relatively small opening which produced two problems: very little light was able to enter and sources that were close together would have been difficult to distinguish due to the effects of diffraction
• Diffraction


  The slight bending of light as it passes around the edge of an object
• Diffraction


  • The amount of bending depends on the relative size of the wavelength of light to the size of the opening
  • If the opening is much larger than the light's wavelength, the bending will be almost unnoticeable
  • If the two are closer in size or equal, the amount of bending is considerable, and easily seen with the naked eye
• Newton's reflecting telescope


  • Featured a curved mirror that utilized the principles of reflection
  • Advantages: a lens can have the same effect as a prism, causing white light to separate into its component colors which can distort images, reflecting telescopes can be made with very large openings since the light does not pass through the mirror but bounces off its top surface
• Multiwavelength astronomy


  The study of objects in space by analyzing the many wavelengths of EMR they may be emitting (instead of just focusing on the visible light)