Light Flashcards
Electromagnetic waves
Waves made form vibrating electric and magnetic fields that regenerate each other. These waves emanate (move outward) from the vibrating charge
Electromagnetic waves velocity
Electromagnetic wave traveling through space never changes its speed - gravity can change the frequency of light or deflect light, bit it can’t change the speed of light
Radiation frequency
Light is electromagnetic radiation within a particular frequncy range 4.3 x 10^14 to 7 x 10^14 vibrations per second ROYGBIV Red is low frequency (long wavelength)
Electromagnetic spectrum
Classification of electromagnetic waves according to frequency - kHz = low frequency radio waves - MHz = middle of AM radio band - 80-108 MHz = FM radio band - 50 MHz = very high frequency (VHF) ** The frequency of an electromagnetic wave as it vibrates through space is identical to the frequency of the oscillating electric charge generating it. - higher the frequency of the vibrating charge, the shorter the wavelength of radiant energy
Electromagnetic spectrum parts
Radio - microwaves - infrared - visible (ROYGBIV) - ultraviolet, x-ray, gamma ray
Transparent materials
Light is an energy-carrying electromagnetic wave that emanates from vibrating electrons in atoms - the way a receiving material responds when light is incident upon it depends on the frequency of the light and on the natural frequency of the electronss in the material - lass and water allow light to pass though in straight lines
Light speed in transparent materials
C = speed of light (300,000 km/sec) - glass = 0.67c - water = 0.75c - diamond = 0.41c When emerging back into air, it returns to c
Opaque materials
Light is absorbed without reemitting it - vibrations given by light to their atoms and molecules are turned into random kinetic energy (internal energy) - in metal, when light shines on it, electrons vibrate and reflect (shiny appearance) - earth’s atmosphere is opaque to high-frequency UV light
Opaque materials cont
Light incident on a wet surface bounce around inside the transparent wet region before it reaches your eyes, more absorption of light to the wet surface = image of darker surface
Excitation
A more distant electron from the nucleus is in a “higher energy state” or at a “higher energy level” - when many atoms in a material are excited, many photons with many frequencies are emitted that correspond to many different levels excited - characteristic colors of light (neon)
Excited
When an electron is raised to a higher energy level
De-excitation
This is temporary and returns to its lower energy state while emitting radiant energy ** light is emitted when an electron in an atom makes a “quantum jump” form a a higher to a lower energy level
Photon
Pulse of electromagnetic radiation caused by electrons dropping from higher to lower energy levels in an excited atom - frequency of a photon is directly proportional to its energy
Emission spectrum
Distribution of wavelengths in the light from a luminous source - each element has its own characteristic pattern of electron energy levels and emits light with its own characteristic pattern of frequencies
Emission spectra
- each component color is focused at a definite position, according to its frequency. A given frequency corresponds to a definite wavelength - therefore, colors are referred to in terms of their wavelength
Incandescence
Light that is produced as a result of high temperature - it is a form of thermal radiation - contains an infinite number of frequencies, spread smoothly across the spectrum
Absorption spectra
- continuous spectrum interrupted by dark lines or bands that result from the absorption of ight of certain frequencies by a substance through which the radiant energy passes - atoms will most strongly absorb light having the frequencies to which it is tuned - the positions of the dark lines correspond exactly to the positions of lines in an emission spectrum of the same gas - we determine speed of stars by studying the spectra the emit
Fluorescence
Property of certain substances to absorb radiation of one frequency and to re-emit radiation of lower frequency - it occurs when an atom is boosted up to an excited state and loses its energy in two or more downward jumps to a lower energy state
Phosphorescence
A type of light emission that is the same as fluorescence except for a delay between excitation and de-excitation, which provides an afterglow - due to atoms being excited to energy states that do not defy rapidly - glow in the dark objects
Lasers
Light Amplification by Stimulated Emission of Radiation - devices that produce a beam of coherent light - beam of photons of the same frequency, phase, and direction - beam spreads and weakenes very little - all lasers have an active medium (gas, liquid, solid
Lasers cont
- the atoms are excited by an external energy source. When a single photon from an atom that undergoes de-excitation can start a chain reaction such that another atom is struck and stimulating it into emission - light is initially moving in random directions, but is reflected by mirrors. The light that escapes through the more transparent-mirrored end makes up the laser beam
Present lasers
- produce beams from infrared through UV - it is not a source of energy, it is a converter of energy - laser-light frequency are much higher frequencies than radio or television and therefore can carry more info (bar code)
Lasers used medically
- microsurgery - kill cancer cells - interstitial lastre coagulation - pain relief (stimulates release of endorphins) - stimulates health and growth of new tissues
