Waves Part 2

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Waves Part 2

• Phys 4e. Students know radio waves, light, and
  X-rays are different wavelength bands in the
  spectrum of electromagnetic waves whose speed in
  a vacuum is approximately 3 x 108 m/s (186,000
  miles/second).
• Phys 4f. Students know how to identify the
  characteristic properties of waves interference
  (beats), diffraction, refraction, Doppler effect,
  and polarization.

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Electromagnetic Spectrum
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Radio Waves

• Have longest wavelength and lowest frequency
• Uses radio T.V. broadcasting

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Infrared rays

• Light rays with longer wavelength than red light
• Uses cooking, medicine, T.V., remote controls
• Far infrared rays longer waves. Are thermal--gtin
  the form of heat. We get it from sunlight, a
  fire, radiator, etc.
• Near infrared rays shorter waves. NOT thermal.
  Ex remote controls

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Infrared rays

• Which parts of this image do you think have the
  warmest temperature?
• How does the temperature of this mans glasses
  compare to the temperature of his hand?

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Ultraviolet Rays (UV rays)

• UV rays are electromagnetic (EM) waves with
  frequencies slightly higher than visible light.
• Uses food processing, hospitals to kill germs.
• Helps our bodies produce vitamin D

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X-rays

• X-rays are EM waves that are shorter than UV
  rays.
• Uses medicine. Bones absorb x-rays but soft
  tissues do not.
• Lead absorbs x-rays.

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Gamma Rays

• Highest frequency EM wave shortest wavelength.
• Are generated by radioactive atoms and nuclear
  explosions.
• Are produced by the hottest region of the
  universe, supernova explosions, destruction of
  atoms, etc.
• Uses cancer treatment

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Characteristic Properties of Waves
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Reflection

• What is reflection?
• When a wave bounces off an object and changes
  direction this is reflection.

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Interference

• Waves interfere in one of two ways constructive
  interference and destructive interference.

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What is resonance?

• Many objects have a natural frequency vibrates
  in a regular pattern.
• Resonance occurs when whenever a sound wave has
  the same frequency as the natural frequency of an
  object. The sound will cause the object with the
  same natural frequency to vibrate.

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What is sound?

• Sound travels through different media.
• We hear sound which usually travels through air.
  Sound travels through other media as well, such
  as water and various solids.
• Sound travels different speeds in different
  media. Sound typically travels faster in a solid
  than a liquid, and faster in a liquid than a gas.

The denser the medium, the faster sound will
travel. The higher the temperature, the faster
the particles of the medium will move and the
faster the particles will carry the sound.
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What is intensity?

• Sound intensity is the energy that the sound wave
  possesses. The greater the intensity of sound the
  farther the sound will travel and the louder the
  sound will appear.
• Loudness is very closely related to intensity.
  Loudness is the human perception of the sound
  intensity. The unit for loudness is decibels.

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Loudness in Decibels
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How is frequency related to pitch?

• The pitch of a sound wave is directly related to
  frequency. A high-pitched sound has a high
  frequency (a screaming girl). A low-pitched sound
  has a low frequency (a fog-horn).
• A healthy human ear can hear frequencies in the
  range of 20 Hz to 20,000 Hz. Humans cannot hear
  below 20 Hz. Sounds below this frequency are
  termed infrasonic.
• Sounds above 20,000 Hz are termed ultrasonic.
  Some animals, such as dogs, can hear frequencies
  in this range in which humans cannot hear.

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Diffraction

• Diffraction occurs when an object causes a wave
  to change and bend around it.

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Diffraction

• Diffraction also occurs when passing through a
  small opening. Waves diffract and spread out.

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Refraction

• Refraction is the bending of a light as it passes
  from one medium to another.
• A wave travels at different speeds in different
  things. When a wave traveling a certain speed
  moves into another medium, it will either
  increase in speed or decrease in speed, resulting
  in a change in direction.

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Refraction
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Index of refraction

• Index of refraction of a medium is a measure of
  the speed of light in that medium.

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Prism

• Prism is another form of refraction.
• Glass that bends light. Different frequencies are
  bent different amounts light is broken out into
  different colors.

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Doppler Effect

• The Doppler effect is the apparent change in
  frequency detected when the sound is moving
  relative to the hearer.
• http//www.youtube.com/watch?vO5rqMPdQMQ8

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Polarization

• The process of transforming unpolarized light
  into polarized light is known as polarization.

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Polarization

• Unpolarized light-a light wave that is vibrating
  in more than one plane
• Polarized light-a light waves in which the
  vibrations occur in a single plane.