29.3 Photon Energies and the Electromagnetic Spectrum
A photon is a quantum of radiation.
The speed of light is the energy of a single photon.
Energy in eV is useful when working with small systems.
Many calculations will be easier with these.
The radiation is composed of particles.
The first of the characteristics of UV, x rays, and rays, which start with frequencies just above violet in the visible spectrum, was mentioned previously in this book.
These types of radiation have different characteristics than visible light.
The photon energy is larger at high frequencies.
Major categories are shown as a function of photon energy in eV.
There are certain characteristics of EM radiation that are attributable to photon energy alone.
The effects of a photon are dependent on the amount of energy it carries.
This is enough energy to ionize thousands of atoms, since only 10 to 1000 eV are needed per ionization.
A single -ray photon can cause significant damage to biological tissue, killing cells or damaging their ability to reproduce.
Exposure to ionizing radiation can cause cancer when cell reproduction is disrupted.
Cancer cells are sensitive to the disruption caused by ionizing radiation.
Ionizing radiation has positive uses in cancer treatment as well as risks in producing cancer.
Roentgen took the first x-ray images.
The hand is owned by his wife.
Since a collision with a single atom or molecule is unlikely to absorb all the ray's energy, high photon energy allows rays to penetrate materials.
rays can be useful as probes, and they are sometimes used in medical scans.
x rays are slightly less dangerous than rays at lower photon energies.
The German physicist W. C. Roentgen discovered that X rays were ideal for medical use in 1895.
x rays were used for medical diagnostics within a year of their discovery.
The 1901 Nobel Prize was given to Roentgen for his discovery of x rays.
Without having to make detailed calculations of the intermediate steps, we can consider the initial and final forms of energy.
X rays are produced when electrons strike the copper anode.
The particles interact individually with the material they strike.
The electrons ejected from a hot filament in a vacuum tube can be accelerated through a high voltage.
Thermal energy can be converted by the electrons when they strike the anode.
Since the electrons act individually, they are also produced.
The x-ray photon gets the energy of the electron.
Older TV and computer screens as well as x-ray machines have different versions of the CRT, which is a tube with accelerated electrons at the cathode.
The electrons can give all of their energy to a single photon.
The electron is powered by electrical potential energy.
The charge of the electron is the maximum photon energy.
The result can be applied to many similar situations.
If you accelerate a single elementary charge, like that of an electron, through a potential, then its energy in eV has the same numerical value.
A maximum energy of 50 keV can be generated by a 50.0-kV potential.
The x-ray tube can produce up to 100 keV x-ray photons.
Many x-ray tubes have different voltages so that different x rays can be generated.
When electrons strike a material, the X-ray spectrum is obtained.
The bremsstrahlung part of the spectrum is smooth.
Both processes produce x-ray particles.
The spectrum of x rays obtained from an x-ray tube is shown in Figure 29.14.
The spectrum has two distinct features.
The smooth distribution is caused by the electrons being decelerated.
It is apparent that the maximum energy is unlikely, because a curve like this is obtained by detecting many photons.
Characteristic x rays come from different types of anode material.
They are similar to lines in atomic spectrum, which show the energy levels of atoms.
Atomic physics explores phenomena such as x rays.
The de-excitation of atoms is what causes UV.
Electric discharge, nuclear explosion, thermal agitation, and exposure to x rays are some of the processes in which these atoms can be given energy.
The effects of a UV photon are different from those of visible light.
UV has some of the same effects as rays and x rays.
It can cause skin cancer and be used as a sterilizer.
The major difference is that several UV photons are required to disrupt cell reproduction or kill a bacterium, whereas single -ray and X-ray photons can do the same damage.
One of the benefits of UV is that it causes the production of vitamins D and E in the skin, unlike visible light which does not cause this.
Infantile jaundice can be treated by exposing the baby to the sun's UV rays, called phototherapy, which can help prevent the build up of potentially toxic bilirubin in the blood.
Short-wavelength UV is absorbed by air and must be studied in a vacuum.
The equation and appropriate constants can be used to find the photon energy and compare it to the energy information in Table 29.1.
This photon energy can be used to break up a tightly bound molecule since they are bound by 10 eV.
A dozen weakly bound molecules could be destroyed by this photon energy.
The high photon energy of UV causes it to disrupt atoms and molecules.
All but the longest-wavelength UV is easily blocked by sunglasses.
Ozone in the upper atmosphere protects sensitive organisms from the sun's UV rays.
The protection for us from damage to the ozone layer has been reduced by the addition of such chemicals.
The outer electron shells in atoms and Molecules are the order of the energies.
This means that they can be absorbed.
A single photon can cause a nerve impulse in the retina by altering a receptor molecule.
Only atoms and Molecules that have the correct quantized energy step can absorb or emit Photons.
If a red photon encounters a molecule that has an energy step, the photon can be absorbed.
There is an energy step for the red and violet, but there is no energy step for the violet.
There are some noticeable differences between the two ends of the visible spectrum.
Red light is used to illuminate darkrooms where black-and-white film is developed.
Since violet light has a higher photon energy, dyes that absorb violet tend to fade more quickly than dyes that don't.
If you look at some faded posters in a store, you will see that the blues and violets are the last to fade.
Other dyes, such as red and green, absorb blue and violet photons, the higher energies of which break up their weakly bound molecule.
Blue and violet dyes reflect those colors and do not absorb the more energetic photons.
The answer is related to photon energy.
It is nearly impossible to have two photons absorbed at the same time, since individual atoms interact with each other.
Because of its lower photon energy, visible light can sometimes pass through many kilometers of a substance, while higher frequencies like UV, x ray, and rays are absorbed, because they have sufficient photon energy to ionize the material.
If 10.0% of a 100W light bulb's energy output is in the visible range, you can calculate the number of visible photons emitted per second.
If we can find the energy per photon, we can determine the number of photons per second.
The power is given in Watts, which are joules per second.
The power in visible light production is 10% of 100 W.
The number of particles per second is proof that individual particles are insignificant.
quantization becomes essentially continuous or classical on the scale.
It is possible for the eye to see the 100 watt lightbulb in many kilometers away.
IR is strongly absorbed by water because water has many states separated by energies on the order of to well within the IR and microwave energy ranges.
In the IR range, the skin is almost black with an emissivity near 1 because there are many states in water in the skin that can absorb IR photon energies.
Some molecules have this property.
Air is very transparent to many IR frequencies.
microwaves do not extend to as high frequencies as IR does.
Microwave ovens are an efficient way of putting energy into food because food absorbs microwaves more strongly than other materials.
If you want to warm up with a heat lamp or cook pizza in the microwave, you'll need a lot of photons because the IR and microwaves have low energy densities.
It is not possible for visible light, IR, microwaves, and all lower frequencies to produce ionising with a single photon.
When visible, IR, or microwave radiation is hazardous, the hazard is due to huge numbers of photons acting together.
The thermal effects of visible, IR, and microwave radiation can be produced by any heat source.
Strong electric and magnetic fields can be produced by acting together.
The material can be ionized by such fields.
Some people think that living near power lines is bad for one's health, but ongoing studies show that their strengths are not enough to cause damage.
The correlation of ill effects with power lines is not shown in demographic studies.
A decade ago, the American Physical Society issued a report on power-line fields, which concluded that there was no correlation between cancer and power-line fields.
Because of their low photon energy, it is almost impossible to detect individual photons having frequencies below microwave frequencies.
The particles are there.
A continuous wave can be modeled.
At low frequencies, the electric and magnetic fields are not quantized.
Another example of the correspondence principle is this one.
Use red, green, and blue light to make a rainbow.
The wavelength of a beam can be changed.
The light can be viewed as a solid beam or individual photons.