1. Chapter 27 Light

2. All things either reflect or emit light. Emit -- to give off

3. What is light? Particle or wave Newton and most philosophers before him thought that light consisted of particles. Light seemed to move in straight lines instead of spreading out as waves do. Huygens provided evidence that under some circumstances light does spread out. Other scientists later found more evidence to support the wave theory.

4. Then came Einstein In 1905 Einstein published a theory explaining the photoelectric effect. According to this theory, light consists of particles called photons. Photons are massless bundles of concentrated electromagnetic energy.

5. So what is light? Particle or Wave? Light is both a wave and a particle. We call this the dual nature of light. Sometimes light acts as a particle Sometimes light acts as a wave.

6. It was not known whether light travels instantaneously or with finite speed until the late 1600s. The Speed of Light Now we just ask google

7. Measuring the Speed of Light- Michelson in 1880

8. The Results Michelson’s experimental value for the speed of light was 299,920,000 m/sec. We shall use 300,000,000 m/sec. In scientific notation, it is 3x10 8 m/sec. Michelson received the 1907 Nobel Prize in physics for this experiment. He was the first American scientist to receive this prize.

9. Electromagnetic Waves Electromagnetic –Part electric part magnetic. All light is made up of an alternating electric and magnetic field. Light is a small part of what we call the electromagnetic spectrum.

10. The Electromagnetic Spectrum The electromagnetic spectrum consists of: Radio waves Microwaves Infrared Visible light Ultraviolet X-rays Gamma Rays Increasing Frequency Increasing energy Decreasing Wavelength

11. More about light. The light that comes from the sun is made up of many different wavelengths. All light can be broken down into all of the wavelengths that make up the light. All elements have their own signature of light when they burn. Astronomers use this to see what distant stars and galaxies are made of.

12. Continuum, Absorption, Emission

13. Emission Lines Every element has a DIFFERENT finger print.

14. Polarized Light Light being emitted from a source is said to be polarized if all the amplitude of the waves is aligned in the same direction.

15. Try these I like to listen to KSJS on the radio. I tunes my radio to 90.5MHz. What is the wavelength of the station? Visible light ranges from deep red, roughly 700 nm, to violet, roughly 400 nm. Let’s calculate their frequencies. The X-Ray range starts around 3 x 10 16 Hz. What is the wavelength of these waves?