Радијација и својства на светлината

Зрачење и бранови Најголем дел од информациите околу нас ги добиваме во форма на бранови Звукот е форма на бран. Светлината ја добиваме воформа на бран. Енергијата (информацијата) што се пренесува од едно на друго место се нарекува ЗРАЧЕЊЕ.

Информација од космосот Од 1930 година е возможно да се студираат покрај обичната светлина и други зраци пр. radio зраци, X-зраци, gamma зраци, cosmic зраци, neutrinos, Треба да ги осознаеме основните својства на светлината

Што е светлината? Честичка? Бран? Или е и двете

Што е бранот? Не е механички феномен...туку е форма...настаната како резултат на движење на материјата-масата.

бранови: димензии v = f x  Амплитуда A= висина на бранот над “нулта позиција” Бранова должина  = должина на еден циклус Фреквенција f = зачестеност на бранот, поголема бранова должина е пропорционална со помала фреквенција Брзина v= брзина на бран v = f x 

period = 1 / frequency или frequency = 1 / period Фреквенција фреквенција: вибрации на бранот во единица време. единици се Hertz (Hz) 1-Hz = 1 vibration/sec = 1 cycle/sec 103 Hz = kHz (AM radio frequencies) 106 Hz = MHz (FM radio frequencies) Период: време за комплетирање на еден циклус вибрации –инверзно од фреквенција period = 1 / frequency или frequency = 1 / period

Брзина на бран Брзината на бранот зависи од медиумот низ кој бранот патува. Звучните бранови се движат со брзина од 330 – 350 m/s во воздух и 4 пати побрзо низ вода. Брзината на бранот е поврзана со фреквенцијата и со брановата должина на бранот. брзина на бра = frequency x бр.должина

Светлината е бран Светлината е вид на зрачење; тоа е тип на бран што патува низ просторот. Светлосните зраци се фундаментално различни од другите бранови (звучни бранови на пример). На светлината НЕ И ТРЕБА МЕДИУМ за да патува од едно надруго место. Брзината на светлината во вакуум се нарекува брзина на светлината, c. c = 300,000 km/s

Терминологија Радијација: Светлина: Електромагнетно зрачење: Начин на трансфер на енергијата во форма на бран Светлина: Е друг термин за електромагнето зрачење Електромагнетно зрачење: Познато и како светлина, трансферира енергија од едно на друго место Видлива светлина: Електромагнетно зрачење што е видливо за човечкото око Need to understand these

Group Question Determine the wavelength of your group’s favorite radio station. Assume you are 100 km (~60 miles) from the station transmitter. Calculate how long it takes for the radio waves to arrive at your location from the radio station transmitter. Wave speed = frequency x wavelength Speed of light (radio waves) = c = 3x 108m/sec Distance = speed x time x103 Hz (AM radio frequencies) x106 Hz (FM radio frequencies)

Creating Electromagnetic Waves All matter is made up of atoms. Atoms are, in turn, made up of smaller particles: protons, electrons, and neutrons. Two of the elementary particles that make up atoms possess a property described as electrical charge. The charges on each are equal and opposite. electron: - charge proton: + charge

Charged Particle Interactions Any electrically charged object exerts a force on other charged objects. Electrons negatively charged Protons positively charged Like charges repel one another. Unlike charges attract.

Electrical Force Electrical force: is a universal force (every charged particle affects every other charged particle) may be attractive or repulsive force is always directed along the line connecting two charges depends on the product of the two charges depends on the distance between the two charges squared (obeys the “inverse square rule”) Today, physicists describe electric forces in terms of an electrical field produced by the presence of electrical charge.

Charged Particles and Electric Fields Electric field strength proportional to 1/r2 . An electric field extends outward in all directions from any positively charged particle. If a charged particle moves, its electric field changes. The resulting disturbance travels through space as a wave.

Magnetic Fields If an electric field changes with time (let’s say the source charge wiggles), then a magnetic field is created, coupled to the time-variant electric field. Magnetic fields influence behavior of magnetized objects. Earth’s magnetic field causes compass needles to point N bar magnets electromagnets A simplistic explanation of magnetic fields

Electromagnetism Electric and magnetic fields do not exist as independent entities. They are different aspects of a single phenomenon: Electromagnetism (EMR) Together, they constitute an electromagnetic wave that carries energy and information from one part of the universe to another.

Фреквенција и енергија Светлината пренесува енергија (E) низ просторот. Енергијата е поврзана со фреквенцијата на светлосниот бран со релацијата E = hf Каде h = Planck’ова константа Брзината на светлосниот бран v е дефинирана како: v = f а за светлината, c = f така, E е пропорционално со f или E е пропорционално 1/

Создавање на светлината Светлината е создадена преку движење на набиени честички т.е. Честички кои имаат полнеж. Материјата е создадена од атоми, во чија стрултура, пак, има честички кои носат полнеж. Движењето на овие набиени честички создава светлина. Светлина не е само она што го гледаме!!!.

Електромагнетен спектар

Својства на светлината ПОларизација Рефлекција Рефракција Дисперзија Дифракција интерференција

Рефлексија и рефракција Еден изолоран светлосен бран патува по права линија, а тој правец на движење оже да се промени под некои услови, кога бранот наидува на материјална пречка Светлината може да го смени правецот при: рефлекcија од некоја површина, Огледало, објекти рефракција (or bending of a ray of light) as кога зракот патува од еден во друг транспарентен медиум. Молив во чиста вода Светлина низ парче стакло

Дисперзија Електромагнетните бранови може да стапат во интеракција со позитивни или негативни честички од дадена материја и патуваат побавно во било кој медиум отколку во вакуум, поради таквите интеракции Промената во брзината на еден светлосен бран предизвикува бранот да се рефрактира Бидејќи брзината на електромагнетниот бран во даден медиум се менува и зависи од брановата должина, тогаш содржината на рефрактираната светлина зависи од брановата должина. Овој ефект се нарекува дисперзија.

Видлива светлина Дадена призма може да ја разложи белата светлина на нејзините составни компоненти Составена од 7 бои (Roy G. Biv), познато како спектар Red (~ 700 nm or 7000 Å) Orange Yellow Green Blue Indigo Violet (~ 400 nm or 4000 Å) The sequence of colors red, orange, yellow, green, blue, and violet may be remembered by memorizing the name of that fine fellow "ROY G. BV". This was originally "ROY G. BIV", because it used to be common to call the region between blue and violet "indigo". In modern usage, indigo is not usually distinguished as a separate color in the visible spectrum; thus Roy no longer has any vowels in his last name. (from http://csep10.phys.utk.edu/astr162/lect/light/spectrum.html )

Видлив Спектар Red Orange Yellow Green Blue Violet

Интерференција на бранови Interference: способност на два независни брана да се засилат или да се поништат меѓусебно. Constructive interference occurs when two wave motions reinforce each other, resulting in a wave of greater amplitude. Destructive interference occurs when two waves exactly cancel, so that no net motion remains.

Radiation and Temperature What determines the type of electromagnetic radiation emitted by the Sun, stars, and other astronomical objects? Temperature Electromagnetic radiation is emitted when electric charges accelerate, changing either the speed or the direction of their motion. The hotter the object, the faster the atoms move in the object, jostling one another, colliding with more electrons, changing their motions with each collision. Each collision results in the emission of electromagnetic radiation- radio, infrared, visible, ultraviolet, x-rays. How much of each depends on the temperature of the object producing the radiation.

Measuring Temperature Atoms and molecules that make up matter are in constant random motion. Temperature is a direct measure of this internal motion. The higher the temperature, the faster (on average) the random motion of particles in matter. Temperature of an object represents the average thermal energy of particles that make up that object.

TWO MAJOR SCALES °F and °C Fahrenheit scale based on temperature that salt water freezes 0°F (lower than pure water). Related to Celsius (or Centigrade) by the formula: F = 9/5 C + 32 C = 5/9(F - 32). Celsius is the metric temperature scale, and thus the one used by scientists

ABSOLUTE SCALE K AND °C Celsius (originally Centigrade) based on freezing and boiling point of pure water, chosen to be 0°C and 100°C Kelvin based on absolute coldest temperature possible (absolute zero) Related by K = C – 273.15 C = K + 273.15 Kelvin is the SI unit, and thus also used by the scientific community. For a good web page on this, go to: http://zebu.uoregon.edu/~js/glossary/temperature_scale.html

All molecular motion stops Temperature Scales Temperature Scale Hydrogen fuses Water boils Water freezes All molecular motion stops Fahrenheit 18,000,032oF 212oF 32oF -459oF Celsius 10,000,000oC 100oC 0oC -273oC Kelvin 10,000,273 K 273 K 373 K 0 K

Radiation Laws Blackbody Radiation Wien’s Law Stefan-Boltzmann Law Planck Spectrum Characteristics of Radiator Wien’s Law Relates wavelength at which a blackbody emits its maximum energy, max, to the temperature, T, of the blackbody. Stefan-Boltzmann Law Relates total energy emitted per second per square meter by a blackbody, E, to the 4th power of its absolute temperature T.

Blackbody Radiation Consider an idealized object that absorbs all the electromagnetic radiation that falls on it - called a “blackbody.” A blackbody absorbs all energy incident on it and heats up until it is emitting energy at the same rate that it absorbs energy. The equilibrium temperature reached is a function of the total energy striking the blackbody each second.

Characteristics of Blackbody Radiation A blackbody with a temperature higher than absolute zero emits some energy at all frequencies (or wavelengths). A blackbody at higher temperature emits more energy at all frequencies (or wavelengths) than does a cooler one. The higher the temperature of a blackbody, the higher the frequency (the shorter the wavelength) at which the maximum energy is emitted.

Blackbody Radiation Blackbody radiation: the distribution of radiation emitted by any heated object. The curve peaks at a single, well-defined frequency and falls off to lesser values above and below that frequency. The overall shape (intensity vs frequency) is characteristic of the radiation emitted by any object, regardless of its size, shape, composition, or temperature.

Planck Spectrum As an object is heated, the radiation it emits peaks at higher and higher frequencies. Shown here are curves corresponding to temperatures of 300 K (room temperature), 1000 K (glow dull red), 4000 K (red hot), and 7000 K (white hot).

“Red Hot” As something begins to heat-up, there probably isn’t any visible information to tell you it is warming up. Once it starts to glow red, you have learned it’s hot – don’t touch. Like the stove burners. As it continues getting hotter, it changes to orange, then yellow, green, blue and white. White because all visible wavelengths are represented fairly evenly. With light, black is the absence of color (wavelengths), and white is the presence of all color (wavelengths). This is opposite of pigments where white is absences of color and black is all color combined. Rarely will something have a “sharp blackbody peak” in green, which is why it is rare to see.

This relationship is known as Wien’s law. The Sun and stars emit energy that approximates the energy from a blackbody. It is possible to estimate their temperatures by measuring the energy they emit as a function of wavelength - that is, by measuring their color. The wavelength at which a blackbody emits its maximum energy can be calculated by  max = 3,000,000 / T where the wavelength  max is in nanometers (10-9 m) and the temperature T is in kelvin. This relationship is known as Wien’s law.

Hotter objects are brighter and “bluer” than cooler objects. Effect of Temperature Hotter objects are brighter and “bluer” than cooler objects.

Getting Warmer Top picture: a cool gas cloud. 2nd from top: a “cool” infrared emitting star appears reddish. Notice how little the other colors contribute relative to red. 2nd from bottom: our star, the Sun Bottom picture: a star cluster of very hot UV stars. Notice how they appear white.

Electromagnetic Radiation

Problem - Wien’s law The average surface temperature of the Sun is about 5800 K. At what wavelength is maximum energy emitted from the Sun? If T = 5800 K and max = 3,000,000 / T , then max = 3,000,000 / 5800 = 520 nm. 520 nm is at the middle of the visible light portion of the electromagnetic spectrum. The human eye is most sensitive to the wavelengths at which the Sun puts out the most energy.

Stefan-Boltzmann Law If add up the contributions from all parts of the E-M spectrum, obtain the total energy emitted by a blackbody over all wavelengths. That total energy emitted per second per square meter by a blackbody at temperature T is proportional to the 4th power of its absolute temperature. This is known as the Stefan-Boltzmann law, E = T4 where E stands for the total energy and  is a constant number.

Problem - Stefan-Boltzmann Law ET = T4 The average surface temperature of the Sun is about 5800 K. If the Sun were twice as hot, 2 T = 2 x 5800 K = 11,600 K, how much more energy would it radiate than it does now? The energy radiated by the Sun would be 24 or 16 times more than now.

Electromagnetic Spectrum

Electromagnetic Energy from the Sun

Why Do We Need Space Telescopes? Because not all light can make it through the atmosphere – which is a good thing in some cases. Such as Gamma ray, x-ray, and most UV radiation are unable to penetrate the atmosphere and reach down to the ground. If the atmosphere is said to be transparent to a wavelength of light, then that wavelength actually reaches the ground, such as visible light (which is why we see it). Thus, the atmosphere is said to have a window to that wavelength. If the atmosphere is said to be opaque to a wavelength, then it is unable to penetrate the atmosphere and reach the ground. As you can see from the diagram above and on page 71 of your text, some forms of radiation can penetrate to a certain depth, but never actually reach the ground where we are, like infrared.

Opacity of the Atmosphere Only a small fraction of the radiation produced by astronomical objects actually reaches our eyes because atoms and molecules in the Earth's atmosphere absorb certain wavelengths and transmit others. Opacity is proportional to the amount of radiation that is absorbed by the atmosphere. Wavelength (angstroms) Half-Absorption Altitude (km)