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##### Intros
###### Lessons
1. Fundamentals of light
2. Nature of light and introduction to light fundamentals
3. Luminous body Vs. Illuminated body
##### Examples
###### Lessons
1. What is the frequency of red light, $\lambda$ = 635nm?
1. Calculate the distance covered by light in feet for 1ns.
1. What is the length of green light that lasts for 4.0 fs?
2. How many wavelengths of green light ($\lambda$ = 550 nm) are included in such a pulse?
1. Calculate the distance from Earth to the moon knowing that a pulse of light sent to the moon takes 2.562s to return back to Earth.
1. Light takes 16 minutes to cross Earth's orbit (3.0× 1011m). calculate the speed of light
1. What is the illumination on a wall if it is lighted by 1750-lm light bulb which is 1.50 m away from the wall?
1. A lamp is moved from 40cm to 80cm above the pages of a book. What is the illumination before and after the lam is moved?
1. The illumination on desktop is 3.0 × 102lx. The source providing the illumination is 2.0m above the desk. What is the intensity (luminous flux) of the lamp?
###### Topic Notes

In this lesson, we will learn:

• What is light?
• Source of light
• Light is the visible part of electromagnetic waves
• Light range frequencies
• Visible light colors and wavelengths
• Ray model of light
• Solving problems involving the speed of light
• Solving illumination problems

Notes:

Introduction to Light Fundamentals
• Light is emitted and reflected from objects around us
• Light is a small visible part of electromagnetic waves.
• Light travel along straight line in vacuum or other uniform medium
• The nature of light is explained by two models; particle model and wave model
• Light frequency changes upon moving along the electromagnetic spectrum
• Light is the range of frequencies of electromagnetic waves
• Light waves have wavelength about 400nm to 700nm
• Shortest wavelengths are seen as violet light
• Longest wavelengths are seen as red light
• Knowing that light travels along a straight line in vacuum or any uniform medium leads us to the ray model of light.
• A ray of light is a straight line representing the path of a narrow beam of light. Speed of Light
• Speed of light is represented by letter $c$
• Speed of light is constant in the air and is 3.00×108m/s
• Recall the equation $V=\lambda f$ to find the speed of waves, we can modify the equation in terms of speed of light $c=\lambda f$

Luminous body Vs. Illuminated body
• Luminous body emits light waves (sun, lamp)
• Illuminated body reflects waves produced by an outside source (moon, bridge)
• Luminous flux, is the rate at which light is emitted from a source
• Unit of luminous flux is the lumen
• The mount of illumination of a surface called illuminance,

• $E =$ lumens per square meter $= lm/m^{2}$ OR lux, lx
$E = \frac{P}{4 \pi d^{2}}$
$P =$ luminous flux of the source
$d =$ distance between the surface and the source