Homework # 9 Page 121 Questions: 1-4

AIM: How can you describe light? Textbook: Page 117

Light The Wave Nature of Light The Particle Nature of Light

The Nuclear Atom and Unanswered Questions Rutherford’s Model: Did not explain how the atom’s electrons are arranged in the space around the nucleus. Why the negatively charged electrons are not pulled into the atom’s positively charged nucleus. Why atoms of Cl, K and Ar behave the way they do.

How do Cl, Ar and K behave?

Chlorine and Iron (steel wool) Atoms of chlorine react readily with atoms of many other elements.

Argon gas fills the interior of this incandescent bulb. Why is Ar unreactive?

Potassium Potassium is stored in kerosene or oil to prevent its atoms from reacting with the O 2 and H 2 O in the air.

The Wave Nature of Light

Light is given off in a variety of chemical combustion (a) Combustion (C) Cyalume light sticks (B) A lightning bug

Reading: Light is a pair of wave You know that light is an ordinary, everyday phenomenon. But what is it exactly? Scientists (starting with James Clerk Maxwell in 1864) describe light as an electromagnetic wave. That is, light is actually a pair of waves: a wave of electric field and a wave of magnetic field. They travel in the same direction but the up-and-down part of each wave is perpendicular to the other. For this reason light is also called electromagnetic radiation.

Reading: Light is also a photon Light is also a photon: a particle with a definite ‘size’. That light is both a particle and a wave is a difficult idea and scientists have wrestled with the problem for centuries, at least since Isaac Newton wrote about light. In the early years of the twentieth century Albert Einstein and Max Planck showed some compelling reasons to think of light as a particle. In this activity we will deal with light in both ways. The ‘size’ of a photon is its energy. The energy of a photon is directly related to the fact that it is also a wave: its frequency. Fundamentally, light is a form of energy.

1. Light: The Wave – Particle Duality OR

2. Continuous Spectrum

The Electromagnetic Spectrum Frequency increases Wavelength Decreases

3. Electromagnetic Radiation Is a form of energy that exhibits wave like behavior as it travels through space

the FlavorWave Oven work? Radio wavesMicrowaves Infrared WavesVisible light

querels or disintegrations per second. X- rays Gamma rays Ultraviolet rays

3. Electromagnetic Radiation Radio waves Microwaves Infrared Visible light Ultraviolet X-ray Gamma ray

4. Wave Tell me three characteristics to describe a wave

λ lambda

Any of the parts of the wave that are pointing up like mountains are called crests. Any part that is sloping down like a valley is a trough. A. Crests and Troughs

The amplitude is the distance from the trough or peak to the mid-point of a wave. Amplitude is a measure of how big the wave is. B. The Amplitude

C. Frequency (nu) Frequency ( ν ): Measured in Hertz, Hz The number of oscillations per second. ν 857 Hz =857 waves/ sec= 857/s = 857 s -1

c = the speed of light, 3.00 x 10 8 m/s λ = the wavelength in meters (λ is the Greek letter lambda) ν = the frequency of light in Hz (1/s) ( ν is the Greek letter nu) 5. Speed of Light c = λ ν All the electromagnetic waves travel at the same speed, you can use the formula

In the following examples, which has the greatest amplitude? B A C B

The amplitude of this diagram is: 2

1

.7

Remember, Wavelength tells you the type of light And, Amplitude tells you about the intensity of the light

1.The wavelength of the wave in the diagram above is given by letter ______. Answer: A The wavelength is the distance from crest to crest (or from trough to trough) (or between any two corresponding points on adjacent waves).

2. The amplitude of the wave in the diagram above is given by letter _____. Answer: D The amplitude is the distance from rest to crest or from rest to trough.

3. Indicate the interval that represents one full wavelength. a. A to C b. B to D c. A to G d. C to G 3. Answer: D The wavelength is the distance from crest to crest, trough to trough, or from a point on one wave cycle to the corresponding point on the next adjacent wave cycle.

1. Microwaves are used to transmit information. What is the wavelength of a microwave having a frequency of 3.44 x 10 9 Hz? c = λ ν λ = c ν Data C = 3.00 x 10 8 m/s λ = ? ν = 3.44 x 10 9 Hz or 3.44 x 10 9 sec -1

λ = c ν Data λ = ? C = 3.00 x 10 8 m/s ν = 3.44 x 10 9 Hz or 3.44 x 10 9 sec -1 λ = 3.00 x 10 8 m/sec 3.44 x 10 9 sec -1 λ = 8.72 x m

2. Radio station WGBB on Long Island, New York, broadcast its AM signal, a form of electromagnetic radiation, at a frequency of 1240 KHz. What is the wavelength of these radio waves in meters? λ = ? C = 3.00 x 10 8 m/s ν = 1240 x 10 3 sec KHz: K = 10 3 Hz = sec -1

λ = c ν λ = 3.00 x 10 8 m/sec 1240 x 10 3 sec -1 λ = 242 m

3. A certain shade of green light has a wavelength of 550 nm. What is the frequency of this light in hertz? c = λ ν ν = c λ 550 nm x m nm = 550 x m

A certain shade of green light has a wavelength of 550 nm. What is the frequency of this light in hertz? c = λ ν ν = c λ ν = __3.00 x 10 8 m/sec___ 550 x m ν = 5.45 x s -1 ν = 5.5 x Hz