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.