ELECTROMAGNETIC WAVES AND LIGHT. Physics 5 th Six Weeks

Transcription

1 ELECTROMAGNETIC WAVES AND LIGHT Physics 5 th Six Weeks

2 What are Electromagnetic Waves

3 Electromagnetic Waves Sound and water waves are examples of waves resulting from energy being transferred from particle to particle. Some waves do not require matter in order to transfer energy over a distance. Electromagnetic Waves are made by vibrating electric charges, and can travel through space where no matter is present.

4 As Electric charge flows, a magnetic field is created. As the magnetic field flows, Faraday s Principle of Electromagnetic Induction states, an electric field is created. These two forces continue forward like a, braid one creating the other and so on. Electromagnetic Waves travel outward from a vibrating charge in all directions. An electric charge moving back and forth creates electromagnetic waves. Light is considered electromagnetic radiation because both electrical and magnetic fields vibrate in a light wave.

5 Electromagnetic Spectrum Electromagnetic waves can have a wide variety of. frequencies They may vibrate once a second or trillions of times a second. The entire range of electromagnetic wave frequencies is called the Electromagnetic Spectrum. Different parts of the electromagnetic spectrum interact with matter differently, and as a result they have different names. The portion human eyes can see is called, Visible Light but that is only a very small portion of the spectrum. However, the entire range of the electromagnetic spectrum is are forms of. Light EM Radiation is known as Radiant Energy. The Sun radiates both visible & invisible energy. All these forms fall within the scope of the EM Spectrum

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7 Radio Waves & Microwaves Radio Waves are low frequency electromagnetic waves with wavelengths greater than. 1 meter Cell Phone signals, communication with satellites, and RADAR are common use for radio waves. RADAR works when Radio Waves are transmitted toward an object, by measuring the time required for the waves to bounce off the object and return, the position and movement can be determined. EM Waves with a frequency less than, 1 mm but greater than 1 meter are called Microwaves. Microwaves are used in cooking since their electric field causes water molecules in food to flip billions of times each second. The flipping motion causes the food to be heated. Television broadcasts are also sent via microwaves

8 Infrared Waves Infrared Waves are a type of electromagnetic wave with wavelengths between 1 mm and 750 billionths of a meter. Remote controls use infrared waves to communicate with a TV and computers use infrared waves to read a CD-ROM. Hotter objects emit more infrared waves than do cooler objects. This phenomena can be used to sense warm objects in a dark room using special cameras. Below red Infrared means

9 Visible Light Visible Light is the range of electromagnetic waves that you can detect with your eyes. Visible light differs only from radio waves, microwaves, and infrared waves only by its frequency and wavelength. Visible light has wavelengths between 400 billionths to 750 billionths of a meter. Different wavelengths and frequencies of visible light are seen by the eye as different colors. The main or primary colors of visible light (ordered from longest wavelength to smallest wavelength) are Red, Orange, Yellow, Green, Blue, Indigo, Violet. The order can be remembered as ROY G BIV. ROYGBIV is also the order of the visible light spectrum as frequency and energy increases.

10 Retina Vitreous fluid iris Sclera tough white outer coating of the eye Optic nerve lens cornea pupil Ciliary body has ligaments that hold the lens in place & muscles that adjust the shape of the lens. (behind the Iris) Cornea transparent covering which lets light into the eye and helps protect it. Iris donut-shaped organ which gives the eye its color, the iris can change shape to regulate the amount of light entering the eye. Pupil the hole in the center of the iris, through which light enters. Lens semi-rigid structure that focuses light on the retina. Retina The innermost layer of the eye that contains light receptive cells. Optic nerve nerve that sends messages from eye to the brain Tapedum lucidum- filmy layer some animals have which helps amplify light. Vitreous Fluid (or humor) jelly-like fluid that makes up most of the volume of the eye this fluid acts as a liquid lens, helping to focus light onto the retina.

11 A Journey Through the Eye

12 Rod and Cone Cells (in the retina) Rod cells light and dark Only one type Not good at resolving detail There are more rod cells than cone cells (1000x more) Cone Cells - colors 3 types: red, green, & blue Good for resolving fine detail, such as for reading. Good sensitivity. Used for night vision (in the dark you usually have poor sense of color) Poor sensitivity, needs bright light (so usually works best by day) Choroid layer on the back of the eye, behind the retina that Contains a network of blood vessels. Colored so that the retina Appears black, thus preventing reflection of light within the eyeball.

13 Ultraviolet Waves Ultraviolet waves are electromagnetic waves with wavelengths from 400 billionths to 10 billionths of a meter Ultraviolet waves are powerful enough to enter skin cells, potentially causing skin damage (such as sun burns and wrinkling) or cancer. When UV radiation enters cells it damages DNA and protein molecules. This property allows UV to be used to sterilize medical equipment between uses. Some exposure however is healthy, as UV waves striking the skin enables the body to make Vitamin D which is needed for healthy bones and teeth. Certain proteins in bodily fluids (blood, body oils in fingerprints, sweat, etc.) fluoresce or glow when exposed to UV light. This property is useful in criminology.

14 X-Rays and Gamma Rays X-ray and Gamma Rays are ultra high-frequency, ultra low wavelength electromagnetic waves are so energetic that they can travel through matter, breaking molecular bonds as they go through. X-rays are used by doctors since when they flow through the body onto special photographic film. The denser parts (bones for example) absorb more X-rays than less dense tissues, and they show up darker as a result. Gamma Rays are extremely energetic and are usually only produced by nuclear reactions and explosions. In small, focused amounts, gamma rays are used to destroy cancer cells through radiation therapy.

15 Increasing in energy & frequency

16 In the realm of useless knowledge The first X-ray image by Wilhelm Roentgen 1895 of his wife s hand (note the ring). X-ray images were first known as Roentgenograms He found these rays by accident, by first Putting an electric current through a low pressure gas and noticed that an image was formed on a photographic plate placed near the the gas filled tube. Roentgen later dubbed the wave the X-ray, because at this time their true nature was still unknown. FYI The element Roentgenium (Atomic Number 111) that was discovered in 1994, was named for him

17 Behavior of Light Objects can either absorb, reflect, or allow light to pass through them. The type of material an object is made up of determines whether it will absorb, reflect, or allow light to pass through. Opaque materials only absorb and reflect light, keeping any light from passing through them. Translucent materials allow some light to pass through them, but not enough to see clearly through them. Transparent materials allow almost all light that strikes them to move through them.

18 Polarization A smooth even surface reflects light in only one direction, producing a sharp, clean image A rough surface reflects light in many directions, this is called a diffuse reflection thus making it impossible to see a clean, sharp image. Light vibrates back and forth in a straight line since it operates like a transverse wave. Therefore, filters can be used which can allow only light waves vibrating from a certain plane. Polarized light is light in which waves have been filtered to vibrate in only. One direction

19 Polarization of Light

20 Red, green, and blue are also called the Primary Additive Colors since they add to make white light. Visible Light & Colors Red, Green, and Blue are known as the primary colors of light. When light are mixed together in the correct intensity, white light is produced. R + G + B = W The mixing together of these three colors of light with varying amounts of intensity can produce a wide variety of colors.

21 Light mixing & Colors, Yellow, Magenta & Cyan are referred to as the secondary colors of light since they are made by adding equal intensities of two primary colors of light. R + G = Y R + B = M G + B = C

22 Light & Complimentary Colors Any two colors of light that when mixed together in equal intensity produce white light are known as colors Each Primary color of light has a Secondary color of light as its compliment. For example the compliment of red is cyan R + C = R + (B + G) = White Complementary Colors of Light Red and Cyan Green and Magenta Blue and Yellow complimentary

23 Color addition R + G ---> Yellow R + B ---> Magenta B + G ---> Cyan If magenta light and yellow light are added together, will white light be produced? Short answer: No Long answer: magenta + yellow = (R+B)+(R+G) = R + (R+B+G) = R + White = Pink

24 Color Subtraction pigments are materials that can absorb specific frequencies of light. What do you get if you shine white light on a shirt if it contains pigments that absorb blue light? W - B = (R + G + B) - B = R + G = Yellow What do you get if a cyan light is shone on the same shirt? C - B = (G + B) - B = Green

25 Color, pigment, & absorption Note: a blue shirt appears blue because the pigments dying the shirt absorb red & green light (remember that Red & Green make yellow, so a blue shirt would also absorb yellow) Yellow could then be considered negative blue light A green shirt would absorb magenta (red & blue light) Magenta could be considered negative green light A red shirt would absorb cyan (green & blue light) Cyan could be considered as negative red light Therefore, the opposites would also be true: A cyan shirt would absorb red light and reflect cyan (green & blue) A magenta shirt would absorb green light and reflect magenta (red & blue) A yellow shirt would absorb blue light and reflect yellow (red & green)

26 Why is the sky blue?

27 Why is the Sky Blue v2

28 Light and Refraction Recall that waves bend when they enter or leave different types of media The term for the bending of those waves when they do so is known as refraction. Light waves bend as they enter glass and as they exit it. That bending is due to the difference in the average speed of light in glass and in air. Glass of a certain shape can be used to refract light in order to make an image that appears larger, smaller, closer, or farther than the object being viewed.

29 Light and the Doppler Effect Recall that the Doppler Effect is the apparent change in the frequency of a wave due to the motion of the source of the wave (or the receiver). The Doppler Effect results in waves becoming more frequent, and with a shorter wavelength as an object moves closer, and waves becoming less frequent and with higher wavelengths as the object moves further away. As light is a wave, it undergoes the Doppler Effect as other waves do Note: From what we know of light & light waves, it is impossible to travel beyond the speed of light therefore, there are no such things as light bow waves or light shock waves

30 Light and the Doppler Effect The Doppler Effect in light happens all of the time, but at normal speeds it is not very noticeable. However as something moves faster and faster approaching the speed of light the phenomena is more apparent The Doppler Effect in light results in the red shift and the blue shift As an object moves closer it will be blue tinged (due to higher frequency light waves) As an object moves away it will be red tinged (due to the lower frequency light waves)