THE ELECTROMAGNETIC SPECTRUM Chapter 17 in text; Pg 551

LIGHT PHENOMENON Isaac Newton ( ) believed light consisted of particles By 1900 most scientists believed that light behaved as a wave.

THE ELECTROMAGNETIC SPECTRUM The electromagnetic spectrum represents the range of energy from low energy, low frequency radio waves with long wavelengths up to high energy, high frequency gamma waves with small wavelengths.

CONSIDER THIS… Around us, millions of waves are travelling back and forth. Most of these waves aren’t dangerous. The waves are combined together to form something called the Electromagnetic Spectrum (EM Spectrum). Each wave has a certain frequency and wavelength. The less dangerous waves have a low frequency and long wavelength. The further up the spectrum you get, the waves start to have higher frequencies and shorter wavelengths. These waves travel at : C= 3.0 x 10 8 m/s The speed of light

EMS Most of the electromagnetic spectrum is invisible to the human eye.

THE SPECTRUM Radio Waves Microwaves Infrared Visible Ultraviolet X-Rays Gamma Rays Low frequency and long wavelength High frequency and short wavelength About the size of… Buildings Humans Honey bee Pinpoint Protozoans Molecules Atoms Atomic Nuclei These waves aren’t that dangerous These waves are very dangerous

FREQUENCY RANGES OF VISIBLE LIGHT Red light has a frequency of roughly 4.3 × Hz, and a wavelength of about 7.0 × 10 ­7 m (700nm). Violet light, at the other end of the visible range, has nearly double the frequency—7.5 × Hz—and (since the speed of light is the same in either case) just over half the wavelength— 4.0 × 10 ­7 m (400nm).

The radiation to which our eyes are most sensitive has a wavelength near the middle of this range, at about 5.5 x m (550 nm), in the yellow- green region of the spectrum.

It is no coincidence that this wavelength falls within the range of wavelengths at which the Sun emits most of its electromagnetic energy— our eyes have evolved to take greatest advantage of the available light.

The frequency (f) of a wave is the number of waves to cross a point in 1 second (units are Hertz – cycles/sec or sec -1 ) λ is the wavelength- the distance from crest to crest on a wave Remember

The product of wavelength and frequency always equals the speed of light. C = λf Why does this make sense? NOTE: C is a constant value= 3.00 x 10 8 m/s

VISIBLE LIGHT Primary Colors of Light

The colors we see in objects are the colors that are reflected, all other colors are absorbed. A red t-shirt appears red because red is reflected to our eyes and the other colors are absorbed. When all colors are being reflected we see white light (white isn’t really a color)

When all wavelengths of light are being absorbed we see black (black also, isn’t really a color) A false-color image is made when the satellite records data about brightness of the light waves reflecting off the Earth's surface.

These brightnesses are represented by numerical values - and these values can then be color-coded. It is just like painting by number. The next slide shows a true color vs. false color image of the planet Uranus. Satellite images can be gathered in true color (what our eyes would see) and false color (to make it look better)

The true color image on left is how our eyes would see it. The false color image is enhanced to bring out subtle details to make it easier to study Uranus’ cloud structure.

ATOMS AND LIGHT The movement of electrons inside of atoms produces light and other electromagnetic radiation. Sunlight produces every color in the rainbow but… Each element gives off only certain frequencies of light, called spectral lines. In effect each element has its own signature of spectral lines allowing us to identify which element we have or what stars are made of.

Below is a picture of the spectral lines given off by hydrogen. Note there are 3 different frequencies.

The emission spectra makes it possible to identify inaccessible substances. Most of our knowledge of the universe comes from studying the emission spectra of stars. Below is the spectra of a few more elements. Helium

Neon Argon

In a star, there are many elements present. The way we can tell which are there is to look at the spectrum of the star. From spectral lines astronomers can determine not only the element, but the temperature and density of that element in the stardensity Emission lines can also tell us about the magnetic field of the star. The width of the line can tell us how fast the material is movingmagnetic field

If the lines shift back and forth, it means that the star may be orbiting another star - the spectrum will give the information to estimate the mass and size of the star system and the companion star.mass

Around a compact object (black hole, neutron star), the material is heated to the point it gives off X-rays, and the material falls onto the black hole or neutron star. By looking at the spectrum of X-rays being emitted by that object and its surrounding disk, we can learn about these objects.

Albert Einstein returned to the idea that light existed as particles. He proposed that light could be described as quanta of energy that behave as if they were particles. Light quanta are called photons. While it was difficult for scientists to believe (they can be stubborn) it did explain the photoelectric effect (previously a mystery)

PHOTONS

A certain frequency has to be achieved or the effect does not work The photoelectric effect – When light shines on metals, electrons (photoelectrons) are ejected from their surface. Red light will not cause electrons to eject!

The photoelectric effect has practical applications in photoelectrical cells used for solar powered cars, and solar powered calculators.

VIDEO: OVERVIEW OF THE EMS

WAVE “TYPES” OF THE EMS

RADIO WAVES Radio waves are hardly dangerous at all. These are mainly the waves that are travelling around you. Of course, they aren’t visible. But we know they are there because they transmit from certain devices and other devices receive them. Transmitters of radio waves can sometimes be natural. Sparks and lightning transmit radio waves, which is why you get radio interference during a thunderstorm. BBC Transmitter Long wave: Around 1-2km in length Medium wave: Used by BBC Radio 5 (around 100m in length) VHF: ‘Very High Frequency’. 2m in length. Used by BBC Radio 1 UHF: ‘Ultra High Frequency’. Used by Police and TV transmissions. Less than a metre in length.

MICROWAVES Microwaves are a type of wave used by Mobile Phones and of course, a microwave itself. Microwaves are used to cook various types of food, as the molecules vibrate which cause them to become hot. Mobile Phones use microwaves. But because they are small, it needs sight of a transmitter. This is why sometimes you get a low signal on your phone. Microwaves are also used for radar.

INFRARED Infrared waves are given off by hot objects, including yourself! Remote controls use infrared light. You can use infrared light to see in the dark. The police use thermal imaging (which use IR waves) during the night to locate criminals. IR waves are useful for high speed chases because if the criminal leaves the car somewhere and runs, the police will be able to pickup the heat from the car using thermal imaging. The military also use thermal imaging to locate enemies in scopes, usually with snipers. Also used to heat food, lizards…

VISIBLE LIGHT Visible light is what you see. The waves are given off by anything hot enough to glow. A good example of this is the Sun. It is around 5600 degrees. White light is actually a range of colors mixed together to form one. If you pass white light through a prism, the light will refract. Refraction Also called color spectrum

Visible light is a small portion of this spectrum. This is the only part of this energy range that our eyes can detect. What we see is a rainbow of colors. RedOrangeYellowGreenBlueIndigoViolet ROY G BIV

ULTRAVIOLET (UV) Ultraviolet light is given off in great quantities by the Sun which is what causes sunburns. Ultraviolet is used in sun beds, as it ‘tans’ your body. It is also used greatly in detecting forged bank notes. Large doses of UV light can cause skin cancer. The positive to sun exposure is that it aids in the bodies production of Vitamin D. UV light attracts insects so restaurants and fish bars use lamps to attract the insects away from the food then electrocute them. UV Lamp

X-RAYS X-Rays are usually used by doctors to examine your body or a part of your body. This is good for security too, as people can examine your body to check if you have any harmful weapons or substance on you (airports, etc). Over exposure to X-Rays can cause cell damage and a variety of cancers. X-Ray of the skull

GAMMA RAYS The most powerful electromagnetic wave are Gamma waves. Gamma rays can kill living cells, making them very dangerous. However, doctors use them to kill cancer cells. This is called Radiotherapy.

VIDEO TO REVIEW EMS Click on the sun to view