Chapter 14 Light and Color

God said, “Let there be light”; and there was light. And God saw that the light was good: and God divided the light form the darkness.

Genesis 1: 3-4

Theories of Light • Isaac Newton first studies light… • He defined light as particles… • In Newton’s “particle theory of light”, he postulated that light was tiny streams of particles emitted by a light source.

Theories of Light • Other scientists of the time proposed light was a wave.

• The “wave theory of light” postulates that light consists of waves rather than particles.

• During the civil war, James Maxwell demonstrated that light was two transverse waves vibrating at right angles to each other.

Theories of Light • These two waves act together as a single electromagnetic wave…

Theories of Light • Maxwell said that electromagnetic waves are similar to other waves (sound and water)…they undergo reflection, refraction, diffraction, and interference.

• He said they are different in that they do not need a medium, they can travel through the vacuum of space. • Electromagnetic waves are much, much faster also… 300,000 km/s!!!

Theories of Light • Light is a small part of the electromagnetic spectrum… • Maxwell proposed that the spectrum contained other waves as well that were higher and lower in frequency than light.

• Hertz in 1888 proved the existence of radio waves, which are lower in frequency than light and therefore confirmed what Maxwell proposed.

Theories of Light • Maxwell calculated that all electromagnetic waves travel at a speed of 300,000 km/s in empty space… • It can be represented by the equation… c = x f Speed of light = wavelength times frequency

The Dual Nature of Light • Max Planck and Albert Einstein showed that light cannot be simply classified as a wave or particle… • Rather, light has the characteristics of both particles and waves… • Transmitted light is wavelike… • The manner in which light interacts with matter is particle like…

Quantum Theory of Light • The theory that light has both a wave nature and a particle nature is called the quantum theory of light… ..\DSDUQT.mov

Quantum Theory of Light • Quantum theory says that light is tiny bundles of energy called photons… • When interacting with matter, photons act like particles, but when traveling through space, photons act like electromagnetic waves.

The Electromagnetic Spectrum • We can only perceive part of the frequencies of which light is a part… • We can only see “visible light”…

The Electromagnetic Spectrum

The Electromagnetic Spectrum • The spectrum can be divided into seven broad categories from low frequency to high: – Radio waves – Microwaves – Infrared waves – Visible light – Ultraviolet waves – X-rays – Gamma rays

Radio Waves • The lowest frequency waves • Higher frequency waves are used for television..

• Higher still are used for cell phones

Microwaves • Used in microwave ovens • Also used for radar

Infrared Radiation • Best known as heat waves… • Cannot be perceived by our eyes, but it can be felt as warmth • Infrared rays are used to “see” in the dark by solders and police

Visible Light • This is the only part of the spectrum you can see…

Ultraviolet Radiation • Has three categories: UVA UVB UVC • UVC is the most dangerous and is fortunately blocked by our ozone layer… • UV is often used to sterilize medical instruments… • UV rays are necessary to produce vitamin D…

X-rays • X-rays are useful because they can “see” through matter…

Gamma Rays • The most dangerous of the spectrum… • They are very harmful to tissues…

Einstein’s Theory of Relativity • Einstein discovered interesting consequences due to the speed of light in a vacuum being constant.

Einstein’s Theory of Relativity • He called them his “Theory of Relativity” 1. all motion must be measured relative to some reference point.

2. the speed of light is constant relative to any observer.

Einstein’s Theory of Relativity • These principles lead to bizarre things happening when traveling at speeds close to the speed of light… 1. Time dilation: Time slows down for the object moving at high speeds.

Einstein’s Theory of Relativity 2. Length contraction: Objects appear shorter in the direction of the motion.

• Slow speed • Super fast!

Einstein’s Theory of Relativity 3. Mass increase: the mass of the object moving at high speeds increases.

A Universal Speed Limit • The speed of light is considered a universal speed limit… • Nothing in the physical universe can move faster than the speed of light in a vacuum.

Gravitational Effects • Einstein showed that time and length are also affected by gravity.

Gravitational Effects • Time runs more slowly the greater the gravitational field.

Gravitational Effects • Length is contracted.

The End