Physics and the Quantum Mechanical Model

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Physics and the Quantum
Mechanical Model
Light and Atomic Spectra
What is Light??
• What do you think light is? Can you describe
it??
• Isaac Newton (1642-1727) thought of light as
consisting of particles.
• By the year 1900, however, most scientists
accepted the idea that light was a wave
phenomenon.
Light as a WAVE
• According to the wave model, light consists of
electromagnetic waves.
• Electromagnetic Radiation – includes radio waves,
microwaves, infrared waves, visible light,
ultraviolet waves, x-rays, and gamma rays.
• All light travels at 3.0x108m/s (or _____________)
The Wave Cycle
• Each complete wave cycle has several
important parts
• The amplitude is the wave’s height from the
origin to the crest
• The wavelength (denoted “λ”) is the distance
between crests.
• The frequency (denoted “ν”) is the number of
wave cycles to pass a given point in a specified
amount of time
Wave Cycle
Wavelength and Frequency
• The frequency and wavelength are inversely
related… meaning as one ____________ the
other ____________.
• As the wavelength increases, the frequency
decreases.
• The product (multiplication) of these two
values ALWAYS equals a constant (c) which is
known as the ______________________.
Mathematical Relationship
c = λν
c = the speed of light (a constant), 3.0x108m/s
(or 3.0x1010cm/s )
λ = wavelength
ν = frequency, units are cycles per second, or
Hertz (Hz)
Inverse Relationship
The Visible Spectrum
• When light passes through a prism, different
wavelengths separate out into their own
different colors.
• This phenomenal spectrum of colors can be
seen in a rainbow.
• These colors you can see are known as the
VISIBLE SPECTRUM. (ROYGBIV)
The Visible Spectrum
Question??
Which part of the
visible spectrum has
the shortest
wavelength and the
highest frequency??
Violet
Atomic Emission Spectrum
• Each element emits light when excited with
electricity while in its gas/vapor phase.
• The atoms become “excited” when the absorb the
electrical energy, and the “relax” when that
energy is then released again. This release emits
a “spark” of light, unique to that particular
element, known as the Atomic Emission Spectrum.
Atomic Emission Spectrum
Practice
• Calculate the wavelength of the yellow light
emitted by a sodium lamp if the frequency of
the radiation is 5.10x1014 Hz (5.10x1014 s-1)
Practice
**use Figure 13.10, page 373**
• What is the wavelength of radiation with a
frequency of 1.50x1013s-1? Does this radiation
have a longer or shorter wavelength than red
light??
Practice
**use Figure 13.10, page 373**
• What frequency is radiation with a wavelength
of 5.00 x10-6cm? In what region of the
electromagnetic spectrum is this radiation??
*careful with your units!!*
Homework:
• Read Chapter 13, section 3
(page 372-382)
• Complete (on a separate
sheet to turn in) Page 386,
#32-38

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