Electromagnetic Radiation and Matter

When a photon encounters matter:

-It may impart its energy to a bound electron, exciting that electron to a higher energy state within the atom.

-If the photon has enough energy, it can even ionize the atom by causing an electron to leave the atom entirely, giving the atom a positive charge.

When a free electron is captured by an atom:

-The electron loses some of is energy in the form of a photon. This energy, called binding energy.

when an electron in an excited state:

-It descends to a lower energy state in an atom. The photon that is emitted has a frequency that is determined by the change in energy (delta E)of the electron.

Photon-Electron Interaction

An electron can absorb energy from a photon and jump to a higher energy level.

An electron emits energy as a photon when it jumps to a lower energy level.

electrons can absorb the energy from a photon when they collide and that the electron becomes excited and jumps to a higher energy level

when the electron jumps to a lower energy state, the energy is emitted as a photon.- and vice versa

Photon Emission

The energy change between any two orbitals (delta E) in one element is different from the energy changes in other elements. In all cases, however, an electron moving to a lower energy state releases its energy as a photon.

PHOTON ENERGY ABSORPTION BY MATTER:

The frequency of a photon determines how it will interact with the matter it encounters.

For example, if a photon is released from an atom due to an encounters. to from an n = 4 orbital to

n = 2 orbital, then that photon is able to excite an election in another atom of the same element from n = 2 to n= 4.

Photon absorption by an atomic electron occurs in the photoelectric effect process, in which the photon loses its entire energy to an atomic electron which is in turn liberated from the atom. This process requires the incident photon to have an energy greater than the binding energy of an orbital electron.

What is a characteristic photon?

Characteristic photons are created when orbital electrons of target atoms are removed from their shell and outer-shell electrons fill inner-shell vacancies.

Characteristic Photons

v Atoms and molecules preferentially absorb certain photons those with energies equal to the electron excitation changes that are possible in that substance.

v Thus, after radiation passes through a substance , those particular photon energies will be missing from its spectrum, leaving gaps that appear as dark lines. This pattern of dark lines is the absorption spectrum of the substance and is unique to it.

v A substance can later re-emit photons with the same energy values that it previously absorbed. The emitted photons produce an emission spectrum-pattern of bright lines corresponding to the energy given off by the substance.

(Absorb = Release)

² The photons emitted by electrons generate an emission spectrum.

² The photons absorbed by electrons generate an absorption spectrum.

² Each element has its own set of spectral lines.

when electrons jump to a lower energy level, they emit a photon of a specific energy, which we can observe on a spectrum.

when electrons absorb energy from a continuous spectrum and jump to higher energy levels, the corresponding lines are removed from the spectrum.

AURORA BOREALIS:

An aurora, also commonly known as the polar lights, is a natural light display in Earth's sky, predominantly seen in high-latitude regions. Auroras display dynamic patterns of brilliant lights that appear as curtains, rays, spirals, or dynamic flickers covering the entire sky.

Heat and lonization:

visible light and longer wavelengths are generally converted into thermal energy.

EM radiation of shorter wavelengths, such as ultraviolet light, x-rays, and gamma rays, has enough energy to eject electrons from atoms entirely .

These ejected electrons can impart enough energy to break apart atoms and molecules. And has enough energy to ionize matter and break chemical bonds between those in in molecules and other substances is called ionizing radiation.

opacity and Transparency:

Opaque :Matter that absorbs or reflects all incoming radiation in a particular frequency range. Ex, many windows are made of glass that is opaque to UV light.

Transparent: materials permit radiation in a frequency range to transmit through. Ex, Stained class is transparent to one wavelength of visible light while opaque to others.

BLACK BODY:

All physical objects in the universe emit electromagnetic radiation, and this radiation is a function of temperature. As an object gets hotter, the power of the radiation increases, meaning it gets brighter, and the wavelengths of the radiation decrease.

Black-body : is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. The name "black body" is given because it absorbs all colors of light. A black body also emits black-body radiation.

BLACK BODY RADIATION:

Black body radiation: refers to the spectrum of light emitted by any heated object;

common examples include the heating element of a toaster and the filament of a light bulb.

A straightforward example of a black body is a cavity with a small hole in it. The light entering the hole undergoes so many reflections within the cavity walls that no light can ever be reflected out. If the walls are painted black, making them absorptive, the cavity represents a perfect black body.

A black body is an object that absorbs all radiation.

Black body radiation is electromagnetic waves emitted by a black body.

a black body is a theoretical object because there are no objects that absorb absolutely all radiation that falls upon them, a black body is a model to describe an object if it could in fact absorb all radiation. Emitting a spectrum of radiation with a single peaked length .

the amount or intensity of radiation that is emitted by a black body is related to the temperature of the object and is explained by the Stefan-Boltzmann Law . Ex, Infrared Thermometer

- due to our sun’s temperature, the peak wavelength of radiation emitted from the sun is in the visible range of the electromagnetic spectrum.

( A cooler star would have a smaller peak intensity and longer peak wavelength than our sun and a hotter star would have a larger peak intensity and shorter peak wavelength than our sun,)

Damage to Living Cells:

When ionizing radiation interacts with living tissue, it can damage the molecules in the tissue. Cell membranes, organelles, and other parts of the cell may be affected.

Damage to individual cells can be repaired. The damage from repeated exposure to ionizing radiation can accumulate from many photons in a high intensity doss .

If the damage is not repaired, or if the rate of damage to cells exceeds the rate of repair for a long enough period of time, cancer may develop.(Skin Cancer --Melanoma)

damage do DNA

Effects of UV Exposure

The Sun's Damaging Rays UV radiation occurs in three bands: UVA (315-400 m), UVB (280-315 nm) and UVC (100-280 m). Only UVA and UVB radiation reach Earth's surface and interact with human tissue; UVC is absorbed by ozone in Earth's atmosphere.

The energy in UVA and UVB is less than in UVC, but lower-energy UVA and UVB rays can still damage skin and eye cells. UV radiation can penetrate clouds, so you can still be exposed to UV radiation on overcast days.

UVA rays penetrate the epidermis and disperse in the dermis. Damage to the dermis contributes to wrinkles and sagging skin.

UVA rays also can lead to eye cataracts.

UVB rays penetrate the epidermis and cause redness and sunburn. UVB radiation can also damage DNA, which increases the risk of skin cancer.

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Sunscreen: protects skin from the damaging energy of both UVA and UVB rays

Some sunscreens contain chemicals that absorb the energy from UV radiation and prevent it from penetrating the skin.

(Sunglasses offer protection for eye from these harmful rays.)

Damage From UV light :

Because of the decrease in atmospheric than it did to ultraviolet radiation reaches Earths face now than it did 40 years ago. Prolonged exposure. if radiation is particularly dangerous to people's skin.

damage From High- Energy Radiation

The danger from an high-energy radiation is dose dependent, and it can be minimized by controlling the cumulative amount of time the exposure was and with the appropriate use of distance and shielding.

Ex, technicians often stand behind a metal wall during radiography to minimize their long-term exposure to the rays.

some parts of the body are more susceptible to radiation. cells in your stomach and your reproductive organs are constantly dividing and thus have a greater risk of damaged DNA from radiation exposure. For this reason, these organs are often shielded with lead when the body is scanned with high-energy radiation.

DNA Damage From X-rays:

An incoming X-ray photon can damage DNA. If the damaged DNA is not repaired, it can lead to death of the cell (for example, a skin cell) that contains the DNA, I alterations to the DNA sequence (mutations), and even disease.

l High-energy photons/radiation, also known as ionizing radiation, can damage living tissue, such as skin cells.

l Some cells repair themselves after the damage., such as skin cells after a sunburn.

l DNA can be damaged beyond repair causing the cell to die or to become diseased.such as melanoma, can be caused by excessive damage to the DNA of skin cells.

l Ozone absorbs UV radiation, limiting the amount of harmful radiation that reaches the surface of Earth.