1. Chapter 15
Section 2 The Nature of Light
Objectives
Recognize that light has both wave and particle characteristics.
Relate the energy of light to the frequency of electromagnetic waves.
Describe different parts of the electromagnetic spectrum.
Explain how electromagnetic waves are used in communication, medicine, and other areas.

2. Chapter 15 Bellringer Section 2 The Nature of Light
Visible light is composed of waves that have several different wavelengths. What happens to light that passes through a prism?
Why do we see rainbows on rainy days?
An airplane can be detected by radar. When radio waves strike an airplane, they are reflected back to a detector and the airplane shows up on a radar screen. Explain how stealth airplanes fly through the air without being detected by radar.
Radio waves that carry radio station transmissions and gamma rays that destroy cancer cells are both electromagnetic waves. What property makes one wave harmless and the other destructive?

3. Chapter 15 Waves and Particles
Section 2 The Nature of Light
Waves and Particles
The two most commonly used models describe light either as a wave or as a stream of particles.
Light produces interference patterns like water waves.
Light can be modeled as a wave.
This model describes light as transverse waves that do not require a medium in which to travel.
Light waves are also called electromagnetic waves because they consist of changing electric and magnetic fields.

4. Waves and Particles, continued
Chapter 15
Section 2 The Nature of Light
Waves and Particles, continued
The wave model of light explains much of the observed behavior of light.
Light waves may reflect, refract, or diffract.
Light waves also interfere with one another.
The wave model of light cannot explain some observations.
When light strikes a piece of metal, electrons may fly off the metal’s surface.

5. Waves and Particles, continued
Chapter 15
Section 2 The Nature of Light
Waves and Particles, continued
Light can be modeled as a stream of particles.
In the particle model of light, the energy of light is contained in packets called photons.
A photon is a unit or quantum of light.
A beam of light is considered to be a stream of photons.
Photons do not have mass.
The energy in a photon is located in a particular place.

6. The Dual Nature of Light
Chapter 15
Section 2 The Nature of Light
The Dual Nature of Light

7. Waves and Particles, continued
Chapter 15
Section 2 The Nature of Light
Waves and Particles, continued
The model of light used depends on the situation.
The energy of light is proportional to frequency.
The speed of light depends on the medium.

8. Chapter 15
Section 2 The Nature of Light

9. Chapter 15
Section 2 The Nature of Light
Energy of a Photon

10. Waves and Particles, continued
Chapter 15
Section 2 The Nature of Light
Waves and Particles, continued
The brightness of light depends on intensity.
The quantity that measures the amount of light illuminating a surface is called intensity.
Intensity is the rate at which energy flows through a given area of space.
Like the intensity of sound, the intensity of light from a light source decreases as the light spreads out in spherical wave fronts.

11. Chapter 15 Section 2 The Nature of Light Section 2 The Nature of Light
Figure 13, p. 502

12. The Electromagnetic Spectrum , continued
Chapter 15
Section 2 The Nature of Light
The Electromagnetic Spectrum , continued
The electromagnetic spectrum consists of light at all possible energies, frequencies, and wavelengths.
Sunlight contains ultraviolet light.
The invisible light that lies just beyond violet light falls into the ultraviolet (UV) portion of the spectrum.
X rays and gamma rays are used in medicine.
X rays have wavelengths less than 10–8 m.
The highest energy electromagnetic waves are gamma rays.

13. Electromagnetic Spectrum
Chapter 15
Section 2 The Nature of Light
Electromagnetic Spectrum

14. The Electromagnetic Spectrum, continued
Chapter 15
Section 2 The Nature of Light
The Electromagnetic Spectrum, continued
Infrared light can be felt as warmth.
Infrared (IR) wavelengths are slightly longer than red light.
Microwaves are used in cooking and communication.
Microwaves have wavelengths in the range of centimeters.
Radio waves are used in communications and radar.
Radio waves have wavelengths that range from tenths of a meter to millions of meters.
Air-traffic control towers use radar to determine the locations of aircraft.
Radar, radio detection and ranging, is a system that uses reflected radio waves to determine the velocity and location of objects.

15. Electromagnetic Spectrum
Chapter 15
Section 2 The Nature of Light
Electromagnetic Spectrum