Download Waves and Particles, continued Section 2 The Nature of Light

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.
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Chapter 15
Section 2 The Nature of Light
Bellringer
1. Visible light is composed of waves that have several different
wavelengths. What happens to light that passes through a
prism?
2. Why do we see rainbows on rainy days?
3. 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.
4. 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?
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Chapter 15
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.
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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.
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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.
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Chapter 15
Section 2 The Nature of Light
The Dual Nature of Light
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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.
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Chapter 15
Section 2 The Nature of Light
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Chapter 15
Section 2 The Nature of Light
Energy of a Photon
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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.
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Chapter 15
Section 2 The Nature of Light
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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.
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Chapter 15
Section 2 The Nature of Light
Electromagnetic Spectrum
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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.
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Chapter 15
Section 2 The Nature of Light
Electromagnetic Spectrum
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