What is light?

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

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

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

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

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?

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

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

Objects are TRANSPARENT, TRANSLUCENT AND OPAQUE to light

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

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

Calculations for Light

Speed of light (ALL EM WAVES) c = f λ c = f λWhere –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

Calculating Speed of Light? Who, when, and how Ancient Greeks: light travels instantaneously Ancient Greeks: light travels instantaneously Galileo: hypothesized light had a finite speed and realized it was faster than sound but his method was not sensitive enough to measure (Uncovering lanterns) Galileo: hypothesized light had a finite speed and realized it was faster than sound but his method was not sensitive enough to measure (Uncovering lanterns) Olaus Roemer (danish) ~1670 determined light speed was finite. He was studying the time of eclipse of Io (one of Jupiter’s moons) and noticed time discrepancies. Calculated 220,000,000m/s. (Huygens conferred with him) Olaus Roemer (danish) ~1670 determined light speed was finite. He was studying the time of eclipse of Io (one of Jupiter’s moons) and noticed time discrepancies. Calculated 220,000,000m/s. (Huygens conferred with him)

When Earth and Jupiter are on the same side of the sun (E1 and J1 in Figure), eclipses occur ahead of schedule by up to 11 mins; when on opposite sides of sun, they are delayed by up to 11 mins When Earth and Jupiter are on the same side of the sun (E1 and J1 in Figure), eclipses occur ahead of schedule by up to 11 mins; when on opposite sides of sun, they are delayed by up to 11 mins Olaus Roemer Olaus Roemer Olaus Roemer Olaus Roemer

Albert Michelson (USA 1926) First ran experiments at 27yrs, then again 47 yrs later at age 74. Calculated time for light to make a round trip between 2 mountains in California 35 km apart. Awarded Nobel Prize. His value was 299,799,600 m/s Albert Michelson (USA 1926) First ran experiments at 27yrs, then again 47 yrs later at age 74. Calculated time for light to make a round trip between 2 mountains in California 35 km apart. Awarded Nobel Prize. His value was 299,799,600 m/s The actual value for light (as determined with lasers, atomic clocks and in a vacuum) is 299,792,458 m/s The actual value for light (as determined with lasers, atomic clocks and in a vacuum) is 299,792,458 m/s

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

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

Visible Spectrum Visible 400 nm 700 nm 7.5 x Hz 4.3 x Hz Violet Red High Freq, Short λLow Freq, Long λ

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___________

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

Radio Waves As big as Made by

Microwaves As big as Made by.

Infrared As big as Made by

Visible Light As big as Made by

Ultraviolet As big as Made by

X-rays As big as Made by

Gamma Rays As big as Made by No Picture Available

Example 1:The wavelength of an electromagnetic wave measures 3.63 x 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 m) f = (3.00 x 10 8 m/s) / (3.63 x m) f = 8.26 x Hz f = 8.26 x Hz UV UV

Eye anatomy Biologix: The eye Vision and Perception Eye anatomy Biologix: The eye Vision and Perception (29min) Eye anatomy Biologix: The eye Vision and Perception

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

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

Cone cells: detect color 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.)

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

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

Luminous objects fluorescence fluorescence Phosphorescence Phosphorescence Incandescence Incandescence