The Electromagnetic Spectrum and Visible Light

The Electromagnetic Spectrum

Overview of Electromagnetic Radiation

The electromagnetic spectrum is a continuum of electromagnetic radiation that includes all wavelengths and frequencies. Electromagnetic radiation is the flow of energy through space as electric and magnetic fields oscillate perpendicular to each other.

• Electromagnetic Radiation: Energy that travels at the speed of light (c) through space as oscillating electric and magnetic fields.

• Physicists such as Max Planck and Albert Einstein described this radiation as being made of discrete packets called photons.

• Each photon carries a specific amount of energy, which depends on its frequency.

Wavelength, Frequency, and Energy

• Wavelength (λ): The distance between two consecutive peaks of a wave, usually measured in meters (m), nanometers (nm), or other units.

• Frequency (ν): The number of wave cycles that pass a given point per second, measured in hertz (Hz) or s-1.

• Energy (E): The energy of a photon is directly proportional to its frequency and inversely proportional to its wavelength.

The relationships are given by the following equations:

• Speed of light: $c = \lambda \nu$

• Photon energy: $E = h\nu$

Where:

• $c$ = speed of light ($3.00 \times 10^8$ m/s)

• $\lambda$ = wavelength

• $\nu$ = frequency

• $h$ = Planck's constant ($6.626 \times 10^{-34}$ J·s)

Regions of the Electromagnetic Spectrum

The electromagnetic spectrum is divided into several regions based on wavelength and frequency:

Region	Wavelength Range	Frequency Range	Example Uses
Radio Waves	> 1 m	< 3 × 108 Hz	Broadcast radio, TV
Microwaves	1 mm – 1 m	3 × 108 – 3 × 1011 Hz	Microwave ovens, radar
Infrared (IR)	700 nm – 1 mm	3 × 1011 – 4 × 1014 Hz	Remote controls, thermal imaging
Visible Light	400 – 700 nm	4 × 1014 – 7.5 × 1014 Hz	Human vision
Ultraviolet (UV)	10 nm – 400 nm	7.5 × 1014 – 3 × 1016 Hz	Sunburn, sterilization
X-Rays	0.01 nm – 10 nm	3 × 1016 – 3 × 1019 Hz	Medical imaging
Gamma Rays	< 0.01 nm	> 3 × 1019 Hz	Cancer treatment, nuclear reactions

Mnemonic for Spectrum Order

• Mnemonic: "Large Radio Martians Invaded Very Unusual X-Ray Guns"

• This helps remember the order: Radio, Microwave, Infrared, Visible, Ultraviolet, X-Ray, Gamma

Energy and Frequency Relationship

• As you move from radio waves to gamma rays, wavelength decreases and frequency increases.

• Higher frequency radiation (e.g., X-rays, gamma rays) carries more energy per photon.

• Lower frequency radiation (e.g., radio waves) carries less energy per photon.

Visible Light Spectrum

The visible light spectrum is the small portion of the electromagnetic spectrum that can be detected by the human eye, ranging from approximately 400 nm (violet) to 700 nm (red).

• Red: ~700 nm (lowest energy, longest wavelength)

• Violet: ~400 nm (highest energy, shortest wavelength)

• Colors in order: Red, Orange, Yellow, Green, Blue, Indigo, Violet

Key Equations

• Relationship between wavelength and frequency: $c = \lambda \nu$

• Energy of a photon: $E = h\nu$

Examples and Applications

• Example: Which kind of electromagnetic radiation contains the greatest amount of energy per atom?

  • Answer: X-Ray (since energy increases with frequency and X-rays have higher frequency than microwaves, radios, ultraviolet, and infrared)

• Practice: Which of the following sources of electromagnetic radiation will have the highest energy?

  • Given options: Light A (595 nm), Light B (0.0333 cm), Light C (0.000150 m), Light D (291 nm)

  • Answer: Light D (291 nm) – shortest wavelength, highest energy

Practice Problems

• Problem: A carbon-oxygen double bond within a sugar molecule absorbs electromagnetic radiation at a frequency of $6.0 \times 10^{13}$ s-1. What portion of the electromagnetic spectrum does this represent?

  • Answer: Infrared (IR)

• Problem: X-Ray detectors use oscillators to convert X-rays into light. Which of the following would be picked up by an X-Ray detector: radiation with a wavelength of 0.85 nm or a frequency of $6.52 \times 10^{17}$ s-1?

  • Both values fall within the X-ray region of the spectrum.

Additional info: The notes include both conceptual explanations and practice questions, making them suitable for GOB Chemistry students studying the electromagnetic spectrum and its applications.