S2 2.1 The Electromagnetic Spectrum

2.1 The Electromagnetic Spectrum

The Electromagnetic Spectrum

• ​The first person in the world to figure out that light was an electromagnetic wave was James Clerk Maxwell.

• Electromagnetic waves are transverse waves caused by changing electric and magnetic fields.

• Since these waves consist of fields in space and not an interaction of matter, they don't require a medium to propagate and can travel through the vacuum of space.

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The Electromagnetic Spectrum

• ​The full range of frequencies of electromagnetic waves is called the electromagnetic spectrum.

• The electromagnetic spectrum contains the spectrum of visible light and several forms of radiation that aren't visible.

• The visible spectrum consists of different frequencies of light corresponding to different colors.

Multiple Choice

Microwaves, gamma rays, and radio waves are all types of what?

• Electromagnetic waves
• Types of electronics

• Mechanical waves

• Oppenheimer's pet's names

Drag and Drop

Light consists of oscillating ​

Placeholder

(E) and ​

Placeholder

(B) fields.​

Drag these tiles and drop them in the correct blank above

electric

magnetic

beta

blue

red

electromagnetic

infrared

ultraviolet

Dropdown

Light in a vacuum always moves at about

Select answer

m/s

Origin of Light

• ​Electrons in an atom emit light when they move from a higher energy level to a lower energy level.

• The frequency of the emitted light is directly proportional to the energy given off by the electrons.

• The higher the energy given off by the electron transition, the higher the frequency of the emitted light.

• This energy is expressed by the equation E = hf, where h represents Planck's constant, which is 6.626×10^-34 Joule seconds (Js).

Common Light Source: Blackbody Radiation

• ​A blackbody absorbs all the radiation incident upon it, heats up, and then re-radiates energy.

• The spectrum of blackbody radiation depends only on the body's temperature, and not on the type of radiation incident upon it.

• When blackbodies emit radiation, they glow to a certain extent, such as burning coals, incandescent light bulbs, and the sun.

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Common Light Source: Fluorescence

• Fluorescence is the emission of light caused by the excitation of atoms in a substance.

• In fluorescence, a substance absorbs light at a particular wavelength and nearly immediately emits light of longer wavelength.

• The emission spectrum produces discrete frequencies for specific glowing gases, such as those from a mercury vapor lamp.

Common Light Source: Light Emitting Diode (LED)

• LEDs are electronic devices that give off light in specific bands of energy, which is a very efficient way to generate light.

• In a LED, the recombination of electrons and electron holes in a semiconductor produces light in a process called electroluminescence

• The wavelength of the light depends on the energy band gap of the semiconductors used.

Visisble Light

• When white light passes through a prism, it is split apart into its separate wavelengths.

• Each wavelength is seen as a slightly different color, and each has a specific frequency.

• From lowest frequency to highest, the colors are red, orange, yellow, green, blue, indigo, violet (or Roy G Biv).

• The human eye can see electromagnetic wavelengths from about 380 nm (violet) to 750 nm (red).

Infrared Radiation

• Infrared waves blend with the red light on one end of the visible light spectrum, and have wavelengths of roughly 0.750 to 300 μm.

• Infrared waves with wavelengths closer to the red light are called near infrared, while hose with wavelengths closer to microwaves are called far infrared.

• Night–vision glasses can detect human presence in the dark, because you can see infrared light emitted by skin and by other warm objects.

Ultraviolet Radiation

• Ultraviolet (or UV) radiation has wavelengths roughly from 10 to 400 nm.

• The sun emits UV waves in three recognized energy ranges: UVA, UVB, and UVC.

• UVA have the longest wavelengths, UVB have the next longest, and UVC have the shortest and highest energy wavelengths.

• The atmosphere blocks most of the sun's UV radiation, including all UVC.

• About 95 percent of the UV radiation that reaches Earth is UVA.

Multiple Choice

Infrared waves have higher frequencies than microwaves. Which statement best compares the energy of these two types of waves?

• The energy relates to amplitude only. Frequency has no effect on energy.

• Infrared waves and microwaves have the same energy.
• Infrared waves have higher energy than microwaves.
• Microwaves have higher energy than infrared waves.

Multiple Choice

Which color of the visible light spectrum has the highest frequency and the shortest wavelength?

• Violet
• Red
• Green
• Yellow

Multiple Choice

1. A radio station broadcasts a radio wave with a wavelength of 3.0 meters.  What is the frequency of the wave?

• 200,000,000 Hz
• 50,000,000 Hz
• 1,000,000 Hz
• 100,000,000 Hz

Multiple Choice

1. A TV station broadcasts its signal with a frequency of 60MHz.  What is the wavelength of the wave?

• 5 meters
• 100 meters
• 2 meters
• 10 meters

Reorder

Reorder the following from shortest wavelength to the longest wavelength.

• gamma rays

• x-rays

• ultraviolet

• visible light

• infrared

1

2

3

4

5

• 1
• 2
• 3
• 4
• 5

Match

Match the following

• Radio waves

• Microwaves

• Infrared

• UV rays

• Gamma Rays

Has the longest wavelengths and the lowest frequency

Used in cell phone communication and police radar systems

It is used in thermal imaging

Overexposure to this can result in sunburns and skin cancer

Has the highest energy of all electromagnetic radiation and is the most damaging to human tissue

• Has the longest wavelengths and the lowest frequency

• Used in cell phone communication and police radar systems

• It is used in thermal imaging

• Overexposure to this can result in sunburns and skin cancer

• Has the highest energy of all electromagnetic radiation and is the most damaging to human tissue