General Outcome C2 - Students will describe the properties of the electromagnetic spectrum and their applications in medical technologies, communication systems and remote-sensing technologies used to study the universe.

30–C2.1kdescribe the range of the electromagnetic spectrum from long, low-frequency radio waves through microwaves, infrared (IR) rays, visible light rays and ultraviolet (UV) radiation to very short, high-frequency waves, such as X-rays and gamma rays
30–C2.2k compare and contrast, to each other, the various constituents of the electromagnetic spectrum, on the basis of source, frequency, wavelength and energy, and their effect on living tissue; e.g., UV radiation on human skin and photosynthetic organisms; gamma radiation on living cells; visible light on plants, phytoplankton and humans; artificial illumination on the growth of plants
30–C2.3k recognize that Earth’s atmosphere absorbs certain frequencies of EMR
30–C2.4k investigate and describe, qualitatively, the phenomena of reflection, refraction, diffraction and polarization of visible light
30–C2.5k compare and contrast the properties of radiation, from any region of the electromagnetic spectrum, with those of visible light; i.e., wavelength, frequency, speed, reflection, refraction, diffraction, penetrability
30–C2.6k investigate and describe the relationships of the variables in the universal wave equation v = λ × f
30–C2.7k explain, in general terms, the design of telescopes that are used to gather information about the universe through the collection of as much EMR as possible; i.e., reflecting and refracting optical and radio telescopes
30–C2.8k explain that nuclear fusion in the sun, represented by the equation ²₁H + ²₁H → ³₂He + ¹₀n, produces a wide spectrum of EMR
30–C2.9k describe, in general terms, how a spectroscope can be used to determine the composition of incandescent objects or substances, and the conditions necessary to produce emission (bright line) and absorption (dark line) spectra, in terms of light source and temperature
30–C2.10k describe technologies used to study stars

• spectroscopes used to analyze the distribution of energy in a star’s continuous emission spectrum can be used to estimate the surface temperature of the star
• Doppler-shift technology used to measure the speed of distant stars provides evidence that the universe is expanding

30-C2.11k describe, in general terms, the evolution of stars and the existence of black holes, white dwarves and neutron stars.

2.1 Electromagnetic Radiation

Electromagnetic radiation (EMR) is a vibration of perpendicular (at 90o) electric field and magnetic field.
We can see part of the electromagnetic spectrum as visible light. Other animals can see other parts of the electromagnetic spectrum.
Ex. Some snakes see infrared (IR, heat).
Ex. Butterflies see visible light like us so they look colorful, however moths see ultraviolet (UV) so they look colorful to each other but not us.

Wavelength (λ) – the length of a wave, measured in meters.
Frequency (f) – how many waves (cycles) go past a point in one second, measured in hertz (Hz)
Speed of light (c) – light travels at 3.00×10⁸ m/s
c = f × λ


Example: 4.5 × 10⁴ waves pass a point in 6.2 μs. What is the frequency?
EMR Spectrum

• A continuous spectrum of EMR that we have divided into different parts by use.
• We are very familiar with visible light which is the part of the EMR spectrum we can see.
• The sections naturally blur into each other.
• Parts are separated by legal definitions, and generally by use. For example you can’t just broadcast any radio signal because it might interfere with important signals (GPS, airplane or EMS communications, etc…). A North American radio won’t pick up signals in Europe because they use different frequencies.
• As wavelength increases (gets longer) the energy of the EMR goes down. As the wavelength decreases (gets shorter) the energy of the EMR goes up.
• As the frequency increases (gets higher) the energy of the EMR goes up. As the frequency decrease (gets lower) the energy of the EMR goes down.

Parts of the EMR Spectrum

• Radio Waves
• Radio waves are used for communications, very specific microwaves are used for cooking (they heat water).
• Satellite TV, radio, radar, car key remotes, garage door remotes, Bluetooth, WiFi, cell phones are all examples of sending and receiving radio signals. We all use them every day.
• Microwaves
• Microwaves oven are dangerous only because of the amount of energy used, 750 W. Cell phones use microwaves as well but aren’t dangerous because of the low power 0.003 W. It takes thousands of cell phones to equal the power of a microwave.
• Think of the difference of standing in front of a flash light 10W vs a huge spot light 700W. The spot light will burn you due to the power.
• Infrared Radiation (IR)
• We can feel this a radiant heat. A heat lamp glows red only so that you know that it is on.
• At the agrena the heaters in the stands release IR that people feel, but they don’t glow (visible light) because they are placed where no one will touch them by accident.
• Your cell phone can often see IR. Take a remote control (TV) and look at it while you push a button on your remote. Try both cameras (front and back) as some phone now have IR filters to get a better picture on one of the cameras. Different buttons will produce different flash patterns.
• Visible Light
• We see the light reflected off of object to see color. White is all colors, black is no color.
• Most people can see the full rainbow: ROYGBIV. Some people are color blind and can’t distinguish between some colors.
• Ionizing Radiation
• All sections with frequencies above visible light (UV, X-ray, Gamma ray and cosmic ray) are ionizing radiation. Each wave has enough energy to knock electrons off of atoms and cause a chemical reaction. If the reaction takes place in your cell’s DNA it can cause cancer. This is why they are all dangerous.
• Tanning is your body reacting to the damage caused by UV light. No level of tanning is completely safe. People with darker skin have more melanin which absorbs UV light and protects their cells better than fair skinned people.
• Ultraviolet (UV)
• UV is ionizing radiation that we can use to speed up a chemical reaction. Some chemicals will mix and make plastics and the reaction can be sped up using UV light. For example a dentist.
• Our body uses UV light to process vitamin D, 5 min of face and hands is enough exposure.
• X-Rays
• UV is stopped by skin whereas X-rays go through you. Your bones are dense enough to stop the X-ray. Sometime doctors will inject or have people drink a liquid (barium) that will stop X-rays and allow the doctor to see what soft organs are doing on an X-ray.
• Gamma Rays
• Come from radioactive materials. Extremely high energy and very dangerous. They will kill you not make you big and green.
• Used for research, metal exposed to gamma rays behaves like it is much older for fast metal aging, can “see” through thick metal for welding X-rays.
• Used to kill cancer by concentrating a lethal dose of Gamma Rays on the cancerous tumor but rotates around giving the rest of your body a small radiation dose.
• Gamma rays can be projected into the body from outside. Radioactive elements that release gamma rays can be absorbed , injected or implanted into a patient’s body to directly target tumors.

2.2 Astronomy

Stars

• The natural source of EMR in the universe is stars. Our closest star is called Sol and is better known as our Sun.
• Astronomers observed that our Sun’s light is not exactly the same as other stars. Different stars emit slightly different EMR and scientists wondered why.
• constellation: a group of stars perceived as being in the shape of a figure or a design
• Stars are powered by gravity pulling everything in and nuclear fusion making it hot (15 million oC) and pushing outwards.
• We’ll look at fusion in the next unit.
• Just like the Earth, there are multiple layers to the Sun
• Different parts of the Sun emit different EMR depending on the temperature. The hotter the part the higher the energy and frequency of the emitted EMR.
• Different wavelengths will penetrate the atmosphere to the surface.
• UV, X-rays and Gamma rays are dangerous but fortunately they are absorbed by the atmosphere so they don’t hurt us.
• Due to its wave nature EMR has the properties:
• Refraction – EMR will bend when it goes from one medium (material) to another.
• Reflection – EMR will bounce off of reflective surfaces (flat metal).
• Telescope - To magnify star we use telescopes. A telescope uses a mirror to focus the light energy over a very large area onto the small area of your eye. The reason that you can’t see some stars is they are too dark, there isn’t enough light energy entering your eye to activate your retina cells.
  Modern telescopes use mirrors that are meters across and can see much further out into space. Ideally, we move the telescope into space to avoid atmospheric interference.
• False-Color Images Since we can’t see any EMR other than visible light, some telescopes convert other parts of EMR into visible light so we can see what it senses. NASA’s great observatory program put multiple telescopes into space to measure all parts of the EM spectrum. Several other groups (European Space Agency, Japan, China, Russia) have also made space telescopes.
• Polarization – confining a wave to vibrate in one direction
• Diffraction – The bending of light as it passes through small openings.
• Resolution – being able to distinguish between two light sources
  When lights are close together it is often hard to determine if there are 2 light close together or 1 large light.
• Refraction – using a prism to split light into its spectrum (component colors).

Analyzing Starlight

• When low pressure gasses are heated they emit light. Scientists use diffraction gratings or prisms to split the light into the rainbow of colors.
• They were surprised to notice dark lines in the rainbow.
• With research scientists realized that each element absorbs specific colors. By matching the dark lines to each elements unique pattern, they can identify what elements are in stars, planets, etc.. by looking at them

Doppler Shift

• Waves change frequency if the source is moving.
• This is why the sound of a car changes as it drives past.
• The light of stars is changed due to the doppler shift
• Red shifted stars are moving away from the Earth
• Blue shifted stars are moving towards the Earth
• The light from all stars are red shifted compared to the light from our sun. This means that all stars are moving away from the Earth. This shows that the universe is expanding.

Distances in Space

• One light second is the distance light travels is one second
• 1 ls = 3.00 × 10⁸ m
• The moon is one light second away.
• The sun is 8 light minutes away.
• Pluto is 4 light hours away.
• One light year is the distance light travels in one year
• 1 ly = 9.46 × 10¹⁵ m
• The closest star is 4.24 ly away.
• Our galaxy is 100 000 ly in diameter

Reflection

• Light will bounce off of a mirror.
• By using a curved mirror we can focus the light energy of a large area onto the small area of our eye.
• This concentrates (amplifies) the light energy so our eye can see it.

Our eyes can only see visible light. To see the other parts of the electromagnetic spectrum we use false color images. That is when a computer takes a sensor image and changes it to visible light. Stars

• A star starts as a big ball of hydrogen gas.
• Due to its mass, the force of gravity in the middle is strong enough to crush hydrogen atoms together into helium through nuclear fusion.
• The heat of fusion causes the gas to expand.
• A star is a balance of the force of gravity inwards and the force of the heat expanding outwards.

Life of a Star

Small Star

• Small star < 1.5 * size of our Sun
• Initial fusion starts forming a yellow star.
• Heat expansion forces the star to grow to red giant.
• As a red giant the outside cools and drifts away as a nebula.
• The core forms a white dwarf star.
• Not enough mass to form a black hole, forms a white dwarf.

Large Star

• Large star > 1.5 * size of our Sun
• Initial fusion starts forming a yellow star.
• Rapid heat expansion forces the star to grow to super giant.
• As it expands fusion slows and gravity drives the mass into the center.
• The in rushing gas causes a huge rush of fusion causing a supernova explosion leaving a neutron star or a black hole.
• Has enough mass to cause a supernova and form a neutron star or a black hole.

Chapter 2 Summary

Chapter 2 Review Questions

Unit C Conclusion

Unit C Review Questions