Flashcards in Ch. 3 Electromagnetic Energy Deck (83):
Photons are also known as...
Where does electromagnetic energy exist?
Name some examples of electromagnetic energy
x-rays, visible light, and radiofrequencies
What are properties of electromagnetic energy?
frequency, wavelength, velocity, and amplitude
electromagnetic energy that exists over a wide range is called
an energy continuum
What is an atom of light called?
the smallest quantity of any type of electromagnetic energy
an x-ray photon is a ______ of electromagnetic energy
What properties does visible light have
electric and magnetic properties
how fast is the speed of light?
186,000 miles/second or
3 x 10^8 m/s
Why do physicists use the word field?
to describe interactions among different energies, forces, or masses that can otherwise be described only mathematically
The electric field governs what?
the interaction of electrostatic charges
The magnetic field governs what?
the interaction of magnetic poles
How can sine waves be described?
by a mathematical formula and have many applications in physics
How do electrons behave in a alternating electric current?
they move back and forth sinusoidally through a conductor
it is one half the range from crest to valley over which the sine wave varies
What does a model of electromagnetic energy describe?
variations in the electric and magnetic field as the photon travels with velocity
What are the important properties of the sine wave model?
frequency and wavelength
How is wavelength represented?
with the symbol lambda
The rate of rise and fall
How is frequency usually identified?
cycles per second
What is the unit of measurement for frequency?
One Hz is equal to...
1 cycle per second
Frequency is equal to....
the number of crests or the number of valleys that pass the point of an observer per unit of time
the distance from one crest to another, from one valley to another, or from any point on the sine wave to the next corresponding point
What 3 wave parameters are needed to describe electromagnetic energy?
velocity, frequency, and wavelength
With a given velocity what is the relationship of wavelength and frequency?
they are inversely proportional
What is the wave equation?
velocity = frequency x wavelength
What is the equation for electromagnetic wave?
c=frequency x wavelength
If frequency increases then wavelength
The electromagnetic spectrum includes what/
the entire range of electromagnetic energy
What are the 3 regions of the electromagnetic spectrum that are important to radiography?
visible light, x and gamma rays, and RF
What are all the portions of the electromagnetic spectrum?
visible light, x and gamma rays, RF, ultraviolet light, infrared light, and microwave radiation
What modality is not a part of the electromagnetic spectrum?
How is light measured
How are xrays described (units)
electron volt (eV)
Photons travel in...
What is refraction?
when a photon is deviated from its straight path by going from one transparent medium to another
Visible light makes up how much of the segment of the electromagnetic spectrum
it makes up the smallest segment
Sunlight has 2 types of invisible light called
infrared and ultraviolet
What are the characteristics of infrared light?
it consists of photons with wavelengths longer than those of visible light but shorter than those of microwaves.
What is another name for infrared light?
On the electromagnetic spectrum, where does ultraviolet light fall?
between visible light and ionizing radiation
What light is responsible for sunburn?
ultraviolet light is responsible fore the molecular interactions that cause sunburn
How are communication broadcasts usually identified regarding frequency of transmission?
radiofrequency or RF
RF has low ____ and long ____
How long RF is microwave radiation?
very short wavelength
Do xrays have a higher frequency or lower frequency/wavelength?
higher frequency/much shorter wavelength than other types
xrays are emitted from...
the electron cloud of an atom that has been stimulated artificially
Where do gamma rays come from?
inside the nucleus of a radioactive atom
If a gamma ray and xray have the same energy, can you tell them apart?
How are each identified?
1. visible light
What is the difference between a photon of xradiation and a photon of light?
x-radiation has a much higher frequency and a shorter wavelength than visible light
Why is the differences between x-radiation and visible light so important?
Because they result in differences in the way the photons interact with matter
visible light photons tend to behave more like ____ than ____
x-ray photons tend to behave more like ____ than ____
Both visible light photons and x-ray photons have both types of behavior and this is known as...
When do photons interact most easily with matter?
the the matter is approximately the same size as the photon wavelength
x-rays interact with
electrons and atoms
x-rays behave as though they were
visible light is a ____ ____ of the electromagnetic spectrum
On either side of the visible light spectrum are...
ultraviolet light and infrared light
What kinds of light cannot be detected by the eye?
ultraviolet and infrared
How can we "see" ultraviolet and infrared light?
the visible light spectrum extends from ...
from short wavelength violet radiation through green and yellow to long wavelength red radiation
When a photon of light strikes an object, what happens?
it sets the object's molecules into vibration. The orbital electrons of some atoms of certain molecules are excited to an energy level that is higher than normal. The energy is immediately re-emitted as another photon of light and it is reflected
what determines what wavelengths of light are reflected?
the atomic and molecular structures of any object
visible light behaves like a
With light the shorter the photon wavelength, the what?
higher the photon energy
electromagnetic energy attenuation is the reduction in intensity that results from...
scattering and absorption
Describe something that is radiopaque
structures that absorb x-rays
describe something that is radiolucent
something that transmits x-rays
What is the formula for inverse square law?
I1/I2 = D2^2/D1^2
The decrease in intensity that is inversely proportional to the square of the distance of the object from the source mathematically called...
the inverse square law
The inverse square law can be applied to distances greater than...
7 times the longest dimension of the source
According to the inverse square law if the distance fro the source is doubled, what happens to the intensity of the radiation?
it is reduced to 1/4
According to the inverse square law if the distance is halved the intensity is...
increased by a factor of 4
x-ray energy generally ranges from
10keV to 50 MeV
an x-ray photon can be thought of as containing...
an electric field and magnetic field that vary sinusoidally at right angles to each other with a beginning and end that have diminishing amplitude.
X-rays are created with the __ __ __ and they exist with ___ or not at all.
speed of light; velocity
Who got the Nobel Prize in 1918 for mathematical and physical theories that synthesized our understanding of electromagnetic radiation?
Max Panck, a physicist from Germany