1. Pearson Prentice Hall Physical Science: Concepts in Action
Chapter 18
The Electromagnetic Spectrum and Light

2. 18.1 Electromagnetic Waves
Objectives:
1. Describe the characteristics of electromagnetic waves in a vacuum
2. Calculate the wavelength and frequency of an electromagnetic wave
3. Describe the evidence for the dual nature of electromagnetic radiation
4. Describe how the intensity of light changes with distance from a light source

3. Characteristics of EM Waves
Def: electromagnetic waves are transverse waves consisting of changing electric fields and changing magnetic fields
Def: an electric field is a region of space that exerts electric forces on charged particles
Def: a magnetic field is a region of space that produces magnetic forces
Magnetic forces are produced by magnets, changing electric fields and vibrating charges

4. EM waves can travel through a vacuum as well as through matter
Def: EM radiation is the transfer of energy by EM waves traveling through matter or across space
Light and all EM waves travel at the same speed but the wavelength (λ) & frequency (f) can differ
The speed of light (& all EM waves) is 3.00 x 108 m/s

5. Calculations Speed = wavelength x frequency
For EM waves, speed = 3.0 x 108 m/s
Frequency = speed/wavelength OR f= c/λ
Wavelength = speed/frequency OR λ=c/f
The units for speed (c) are m/s
The unit for wavelength (λ) is m
The unit for frequency (f) is Hz (1/seconds)

6. EM Radiation/ Light Intensity
EM radiation sometimes behaves like a wave and sometimes like a particle
Light, therefore, is classified both as an EM wave and as a particle
Def: a photon is an EM packet of energy
Each photon’s energy is proportional to the frequency of the light
The intensity of light decreases as photons travel farther from the source

7. 18.2 The Electromagnetic Spectrum
Objectives:
1. Rank and classify EM waves based on their f (frequency) and λ (wavelength)
2. Describe the uses for different waves of the EM spectrum

8. Rank and Classify
The prism separates the wavelengths present in sunlight which is visible light
From longest to shortest: ROY G B(I)V
The electromagnetic spectrum includes visible plus invisible radiation
Increasing frequency from left to right (longest to shortest): radio waves, infrared rays, visible light, UV ray, X rays, and gamma rays

9. Uses for EM Waves
Radio waves are used in radio, television, microwaves and radar
The shortest radio waves are microwaves
Radar is an acronym: radio detection and ranging
Radar often uses the Doppler effect to determine how fast something is moving
Infrared rays are used as a source of heat & to discover areas of heat difference

10. Thermograms use infrared to sensors to show differences in temperature of objects
Visible light is used to see, stay safe and communicate
UV rays are used in health, medicine and agriculture
X rays are used in medicine, industry and transportation to make pictures of the inside of solid objects
Gamma rays are used medically to kill cancer cells, make brain pictures and in certain industrial situations such as checking pipelines for cracks or other damage

11. 1. Describe three types of materials that affect the behavior of light
Objectives:
1. Describe three types of materials that affect the behavior of light
2. Explain how light behaves when it enters a new medium

12. Three Types of Materials
The behavior of light is affected by transparent, translucent and opaque materials
Transparent materials transmits light, allowing most light to pass through it
Translucent material scatters light
Opaque material either absorbs or reflects all the light that strikes it
No light passes through opaque materials

13. How Light Behaves
When light strikes a new medium, the light can be reflected, absorbed or transmitted
When light is transmitted, it can be refracted, polarized or scattered
Def: an image is a copy of an object formed by reflected light waves
Def: regular reflection is parallel light waves striking a surface and reflecting all in the same direction

14. Def: diffuse reflection is parallel light waves striking a rough, uneven surface, reflecting in many directions
Def: refraction is the bending of light waves
Def: a mirage is a false, distorted image
Mirages occur due to light traveling faster in hot air than in cool air
It is a form of refraction
Def: polarization is light with waves that vibrate only in one direction
Def: scattering is light redirect as it passes through a medium