PROPERTIES OF LIGHT Objective 1 Distinguish between wave

PROPERTIES OF LIGHT Objective: 1) Distinguish between wave fronts and rays 2) Apply the law of reflection to solve real world problems 3) Explain refraction in terms of Snell’s Law and the index of refraction 4) Relate color vision and light

BELLWORK The table at the left represents the decibel level for several sound sources. Use the table to make comparisons of the intensities of the following sounds. How many times more intense is the front row of a Smashin' Pumpkins concert than a. . the 15 th row of the same concert? b. . the average factory? c. . normal speech? d. . the library after school? e. . the sound which most humans can just barely hear?

• As the car approached with its siren blasting, the pitch of the siren sound (a measure of the siren's frequency) was high; and then suddenly after the car passed by, the pitch of the siren sound was low

The Doppler Effect and Light • A moving light source is said to be red-shifted or blue-shifted. • If an astronomer describes the wavelength of a star to be blue-shifted, is the star moving towards the observatory or away from the observatory?

Light and the Electromagnetic Spectrum • Electromagnetic waves are waves which are capable of traveling through a vacuum. • Electromagnetic waves are produced by a vibrating electric charge and consist of both an electric and a magnetic component. • Electromagnetic waves exist with an enormous range of frequencies. This continuous range of frequencies is known as the electromagnetic spectrum

Visible Light • The visible light spectrum: the type of electromagnetic wave which stimulates the retina of our eyes • The visible light region ranges from 700 nm to 400 nm • This narrow band of visible light is also known as ROYGBIV

Vision: photons of visible light carry the activation energy to bend retinal molecules (derived from Vitamin A, retinol) from the cis- isomer to the trans- isomer. This stimulates the optical nerve so your brain can interpret photons of light as colors and shapes to see.

HOW ARE ELECTROMAGNETIC WAVES DISTINGUISHED FROM MECHANICAL WAVES? A. They can travel through materials and mechanical waves cannot B. They come in a range of frequencies and mechanical waves exist with only certain frequencies C. They can travel through a region void of matter and mechanical waves cannot D. They cannot transport energy and mechanical waves can transport energy E. They have an infinite speed and mechanical waves have a finite speed

INTERPRETING THE ELECTROMAGNETIC SPECTRUM 1. Which region of the electromagnetic spectrum has the highest frequency? 2. Which region of the electromagnetic spectrum has the longest wavelength? 3. Which region of the electromagnetic spectrum will travel with the fastest speed? 4. Which color of the visible light spectrum has the greatest frequency? 5. Which color of the visible light spectrum has the greatest wavelength?

EXAMPLE The Bohr model of the hydrogen atom consists of a proton of mass 1. 67 x 10 -27 kg and an orbiting electron of mass 9. 11 x 10 -31 kg. In one of its orbits, the electron is 5. 3 x 10 -11 m from the proton and in another orbit it is 10. 6 x 10 -11 m from the proton. A. What color of light is emitted by the electron during this transition when it’s wavelength is 656 nm? B. Given that the wavespeed for light = speed of light, c and c= f, at what frequency does the lightwave vibrate? C. If the electron jumps from the larger orbit to the smaller one, what is the change in the gravitational potential energy of the atom? D. The energy transmitted by a wave corresponds to its frequency. E = hν = hf… How does this energy compare to U?

A) The color associated with this wavelength is red (in the Balmer series for hydrogen) B) The frequency is found by f = c/ = (3. 00 x 108 m/s )/ (656 x 10 -9 m) = 4. 57 x 1014 Hz = 4. 57 x 1011 k. Hz

C) The change in gravitational potential energy, DU = U 1 – U 2. Therefore, the atom loses -9. 6 x 10 -58 J of potential energy so the light emitted has 9. 6 x 10 -58 J of Energy.

D) E = hν = (6. 63 x 10 -34 Js)(5. 13 x 1014 s-1) = 3. 03 x 10 -19 J Where did all the energy go? Why is some of the gravitational potential energy “lost”?

INDEPENDENT PRACTICE • P. 498 - 499; 3, 6, 8, 10, 11, 12, 16, 19, 20, 26 • P. 684; 70, 71, 72, 77, 78, 80