Light and Atoms

1
Light and Atoms

• Chapter 3

2
Properties of Light

• It does not need a medium (substance to travel
  through)
• need air or water to
  travel through.
• There is no sound in space

3
Manifestations of Light

• Light can be explained by models
• 1. Light as a _______
• wave A wave consisting
  of alternating electric and magnetic energy.
• Ex. Visible light, color depends on wavelength.
• 2. Light as a ____________.
• Light is also considered a subatomic particle
  that in empty space travels in a straight line at
  the speed of light.
• A particle of visible light or
  other electromagnetic radiation.

4
When to use a specific model?

• Scientist use whichever model best explains the
  properties of light at any given time.
• When they explain how a lens focuses light they
  use the wave model.
• When they want to explain how light bounces off
  of a mirror they use the particle model.
• Light is described as having ____________
  
  _____________.

5
Light and color

• _______________ The portion of electromagnetic
  radiation that the human eye is sensitive to.
• Red, orange, yellow, green, blue, indigo, and
  violet
• The difference in color is due to the difference
  in wavelength.
• Wavelength -
• Wavelengths of light are measured in nanometers.

6
Various Laws related to light

• Wiens law
• Remember higher energy light has higher frequency
  and shorter wavelengths.

7
Various laws related to light

• Stefans law
• When Stefans law and Weins law are both applied
  we are able to determine that as temperature
  increases so does the intensity of light

8
Various laws related to light

• Kirchhoff determined that there are 3 different
  kinds of spectra.
• light we see via a
  prism
• light we see emitted from a
  source. Shows lines from the wavelengths emitted
  by a heated element.
• spectra of light with
  black lines (light that was absorbed by a
  material or gas)
• Kirchhoffs law

9
The Doppler Shift

• If a source of light is in motion, its spectral
  lines shift to new wavelengths.
• The Doppler shift results in the

10
Directions of the Doppler Shift

• The shift is an increase in the wavelength if the
  source and observer move apart.
• The shift is a decrease in wavelength if the
  source and observer approach each other.
• The Doppler shift results in a redshift or
  blueshift.

11
Redshift

• A shift in the wavelength of electromagnetic
  radiation to a longer wavelength. For visible
  light this implies a shift toward the red end of
  the spectrum.
• Redshifts occur when the source moves ________
  from the observer or when the observer moves away
  from the source.
• If a star moves away from the Earth then its
  light will appear more red.

12
Blueshift

• A shift in the wavelength of electromagnetic
  radiation to a shorter wavelength. For the
  visible light, this implies a shift toward the
  blue end of the spectrum.
• The shift can be caused by the motion of the
  source of radiation ____________ the observer or
  by the motion of the observer toward the source.
• A star moving ________ the Earth will exhibit a
  blueshift.

13

• Our atmosphere also bends light waves so that
  most stars have a similar appearance regardless
  of what spectra of light they may be emitting.

14
Blackbodies

• A blackbody is an object that absorbs all light
  that falls on it.
• No electromagnetic radiation passes through it
  and none is reflected.
• Because no light is reflected or transmitted, the
  object appears black when it is cold.

15
Blackbodies (Continued)

• When a blackbody is hot, it is a source of
  thermal radiation.
• Incandescent light bulbs are an example of black
  bodies.
• The Sun is also an example of a Blackbody
• When a Blackbody is hot enough to emit radiation,
  it is termed blackbody radiation
• When hot gases emit radiation it is termed
  emission-line radiation

16
Blackbody Radiation

• At room temperature, black bodies emit infrared
  light.
• As temperature increases past a few hundred
  degrees Celsius, black bodies start to emit at
  visible wavelengths of light
• Blackbody radiation in the visible spectra ranges
  from red, through orange, yellow, and white
  before ending up at blue,
• Beyond blue light, the emission includes
  increasing amounts of ultraviolet light.

17
Parts of the Atom

• Positively charged particles
  found in the nucleus of an atom.
• The identity of an atom is determined by the
  number of protons found in the nucleus.
• Neutrally charged particles
  found in the nucleus of an atom.
• Negatively charged particles
  spinning around the nucleus of the atom.