18.1 The Electromagnetic Spectrum

Chapter 18 Objectives  Calculate the frequency or wavelength of light when given one of the two.  Describe the relationship between frequency, energy, color, and wavelength.  Identify at least three different waves of the electromagnetic spectrum and an application of each.  Interpret the interference pattern from a diffraction grating.  Use the concept of polarization to explain what happens as light passes through two polarizers.  Describe at least two implications of special relativity with regards to energy, time, mass, or distance.

Chapter 18 Vocabulary Terms  diffraction grating  electromagnetic  spectrum  electromagnetic wave  gamma ray  inference pattern  microwave  polarization  polarizer  radio wave  rest energy  special relativity  spectrometer  spectrum  time dilation  transmission axis  visible light  x-ray

Inv 18.1 The Electromagnetic Spectrum Investigation Key Question: What is the electromagnetic spectrum?

 The energy field created by electricity and magnetism can oscillate and it supports waves that move.  These waves are called electromagnetic waves The Electromagnetic Spectrum

 Electromagnetic waves have both an electric part and a magnetic part and the two parts exchange energy back and forth.  A 3-D view of an electromagnetic wave shows the electric and magnetic portions The Electromagnetic Spectrum  The wavelength and amplitude of the waves are labeled λ and A, respectively.

 The higher the frequency of the light, the higher the energy of the wave.  Since color is related to energy, there is also a direct relation between color, frequency, and wavelength The Electromagnetic Spectrum

The speed of light waves  The speed of light is incredibly fast (3 × 10 8 m/s) and is represented by its own symbol, c.  The index of refraction (n), is actually the ratio of the speed of light in a material to the speed of light in a vacuum.  The passage of light through matter takes more time because the light is absorbed and re- emitted to pass through neighboring atoms.

18.1 Speed of Light c = f Wavelength (m) Frequency (Hz) Speed of light 3 x 10 8 m/sec

 You are asked for wavelength.  You are given frequency.  Use speed of light, c = ƒ  Solve = c ÷ƒ  = (3 x 10 8 m/s) ÷ ( 600 x Hz)  = 5 x m Calculating wavelength Calculate the wavelength in air of blue-green light that has a frequency of 600 × 1012 Hz.

18.1 Waves of the electromagnetic spectrum  Visible light is a small part of the energy range of electromagnetic waves.  The whole range is called the electromagnetic spectrum and visible light is in the middle of it.

 Radio waves are on the low- frequency end of the spectrum.  Microwaves range in length from approximately 30 cm (about 12 inches) to about 1 mm.  The infrared region (IR) of the electromagnetic spectrum lies between microwaves and visible light Waves of the electromagnetic spectrum

18.1 Medium to high-energy waves  Ultraviolet radiation has a range of wavelengths from 400 down to about 10 nm.  X-rays are high-frequency waves that have great penetrating power and are used extensively in medical and manufacturing applications.  Gamma rays are generated in nuclear reactions.