Light is an electromagnetic wave (EM)

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Alexander Briggs
5 years ago
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1 What is light?

2 Light is a form of energy. Light travels in a straight line Light speed is 3.0 x 10 8 m/s Light is carried by photons Light can travel through a vacuum Light is a transverse wave Light is an electromagnetic wave (EM)

3 All electromagnetic waves are transverse waves. They have electric and magnetic components which vibrate perpendicular to each other.

4 Dual Nature of Light Light is a Particle and a Wave! Light behaves like a wave when it travels in empty space. Light behaves like a particle when it interacts with matter.

5 What can you see? Light is the ONLY thing you see! All visible objects either emit (luminous) or reflect light (illuminated).

6 The objects which we see can be placed into one of two categories 1. Luminous objects are objects which generate their own light. (Sun) 2. Illuminated objects are objects which are capable of reflecting light to our eyes. (Moon) What are we? And what does it mean to reflect? Are mirrors required?

7 The bottom line is: without light, there would be no sight.

8 When light strikes an object it can be REFLECTED, TRANSMITTED or ABSORBED.

9 Objects are TRANSPARENT, TRANSLUCENT AND OPAQUE to light

10 Transparent: all light transmitted Transulcent: some light transmitted Opaque: no light transmitted

11 Ultraviolet light oscillates at too high a frequency for electrons in glass molecules, while infrared is too low. Visible light is just right. Making glass transparent to visible light and opaque to infrared and ultraviolet

12 Calculations for Light

13 Speed of light (ALL EM WAVES) c = f λ Where c is the speed of light in m/s in a vacuum f is frequency in hertz λ is wavelength in meters c = 3.00 x 10 8 m/s

14 Since all EM WAVES travel at same speed, the only difference between them is wavelength, frequecny and energy

17 "Courtesy of the Advanced Light Source, Berkeley Lab."

19 Refer to the chart of the EM Spectrum answer the following: As wavelength increases, frequency and energy As frequency increases, wavelength and energy Longest EM Wave Shortest EM Wave Longest Visible Light Color Shortest Visible Light Color

20 Refer to the chart of the EM Spectrum answer the following: As wavelength increases, frequency decreases and energy decreases As frequency increases, wavelength decreases and energy increases Longest EM Wave radio Shortest EM Wave gamma ray Longest Visible Light Color red Shortest Visible Light Color violet

21 740nm 370nm

22 Wavelength: 1m to m Frequency: 3 x 10 9 to 3 x 10 4 Hz Uses: Telecommunications, TV, Radio Dangers: none

23 Radio Waves Made by As big as

24 Wavelength: 0.001m to 1m Frequency: 3 x to 3 x 10 9 Hz Uses: Telecommunications, RADAR, Cooking Dangers: can produce burns, cataracts, cancer (?)

25 Microwaves Made by As big as.

26 Wavelength: 740nm to 0.01m Frequency: 4 x to 3 x Hz Uses: Heating, cooking, TV remotes, night-vision Dangers: can burn

27 Infrared Made by As big as

28 Wavelength: 370nm (violet) to 740nm (red) Frequency: 8 x to 4 x Hz Uses: seeing Dangers: eye damage from bright lights Visible light is best at getting through our atmosphere which is why we use it to see!

29 Visible Light Made by As big as

30 Wavelength: 10-9 m to 370nm Frequency: 3 x to 8 x Hz Uses: discos, tanning salons, counterfeit detections, pollination Dangers: skin cancer Bees see in UV to help them find pollen!

31 Ultraviolet Made by As big as

Wavelength: 10-12 to 10-7 m Frequency: 3 x 10 20 to 3

32 Wavelength: to 10-7 m Frequency: 3 x to 3 x Hz Uses: medical imagery, security Dangers: cancer Hand with Rings by Wilhelm Röntgen. The first "medical" X-ray of his wife's hand taken on 22 December 1895.

33 X-rays Made by As big as

34 Wavelength: to 10-9 m Frequency: 3 x to 3 x Hz Uses: cancer treatment, observing the universe Dangers: cancer ( )

35 Gamma Rays No Made by Picture Available As big as

36 The Dangers of the EM Spectrum As the wavelength of EM spectrum changes, the way the different wavelengths interact with matter also changes. As the frequency increases, wavelength gets smaller. Eventually the waves are so small that they can interact with cells, DNA and atoms. This is called IONISING RADIATION. NON-IONISING IONISING

37 Example 1: The wavelength of an electromagnetic wave measures 3.63 x 10-9 m. What is the frequency of this waveform? Is it an infrared wave? Why or Why not? f = (3.00 x 10 8 m/s) / (3.63 x 10-9 m) f = 8.26 x Hz UV

38 How we see Color and Intensity sensitive cells on retina image inverted due to refraction by lens. Signal sent to brain via optic nerve

39 Rod Cells: sensitive to brightness Obeys inverse square law Brightness is inversely related to the square of the distance from the source

40 Cone cells: detect color Detect the 3 primary colors of light: red, blue, and green (not to be confused with the primary colors of pigment (red, blue and yellow) you learned in elementary school.)

41 What we see: In visible spectrum nm If you see red, object absorbs all frequencies of visible light but red, ie object reflects red White: combination of all visible light frequencies, all frequencies reflected Black: combination of all visible light frequencies absorbed, no frequencies reflected

42 Colors of Light Primary Blue Red Green Secondary B + R = Magenta B + G = Cyan R + G = Yellow

Which type of electromagnetic wave has a wavelength longer than that of yellow light? A. Infrared radiation C. X-rays B. Gamma Rays D.

Which type of electromagnetic wave has a wavelength longer than that of yellow light? A. Infrared radiation C. X-rays B. Gamma Rays D. UV Rays Science Starter! 10.14-15.13! THE UNIVERSE AND ELECTROMAGNETIC