Electromagnetic Energy Prepared by: Timothy John D. Matoy

Photons First described by ancient Greeks Today, they are known as electromagnetic Energy No mass, no identifiable form They do have electric and magnetic fields that are continuously changing in sinusoidal fashion.

Photons A photon is the smallest quantity of any type of electromagnetic energy. A photon may be pictured as a small bundle of energy, sometimes called quantum.

James Clerk Maxwell Late in 19th century. Showed that visible light has both electric and magnetic properties, hence the term electromagnetic energy.

Properties of EM Radiation It can travel through empty space. It travels with the speed of light. It travels in a wave-like fashion.

Velocity The velocity of all electromagnetic radiation is 3 x108 m/s or 186,000 miles per second.

Wavelength The distance from one crest to another, from one valley to another, or from any point on the sine wave to the next corresponding point.

Frequency Is the number of wavelength that pass a point of observation per second.

Wave Equation V = λf Velocity = wavelength x frequency

Electromagnetic Wave Equation C = λf Speed of light = wavelength x frequency

Practice problem The highest energy x-ray produced at 120 kVp has a frequency of 2.50 x1019 Hz. What is the wavelength?

Practice Problem What is the frequency of a certain electromagnetic wave with a wavelength of 300 cm?

Sample problem The speed of sound in air is approximately 340 m/s. The highest treble tone that the person can hear is about 20 kHz. What is the wavelength of this sound? 1.7 cm

Electromagnetic Spectrum The frequency range of electromagnetic energy extends from approximately 102 to 1024 Hz. The wavelength are approximately 107 to 10-16 m.

Electromagnetic Spectrum

Visible light What your eye detects Has a wavelength of 4000 to 8000 angstroms 1 angstrom = 1.0 x10-10 m 1 nm = 1.0 x10-9 m = 10 angstrom 400 nm for violet 700 nm for red Refraction, rainbow

Radiofrequency Relatively low energy and relatively very long wavelength

Ionizing Radiation Gamma ray X-ray RF and VL are identified by Frequency Ionizing radiation is identified by energy 80 kVp – produces from 0 to 80 kVp

Wave-Particle Duality Photons interact with matter most easily when matter is approximately the same size as the photon wavelength. All radiation with wavelength longer than those of x-radiation interacts primarily as a wave phenomenon. X-rays interact with electons Uv with molecules VL cones and rods, living cells Microwaves hamburger

Quantum Theory “X-rays are created with the speed of light (c), and they exist with the velocity (c) or they do not exist at all” – Max Planck German physicist Receive a nobel prize in 1918 – whose mathematical and physical theories synthesized. Rel. bet. F and e

Planck’s Quantum Equation E = hf Where: E = photon energy h = Planck’s constant f = photon frequency

The Constant of Proportionality Also known as Planck’s constant (h), has a numeric value of 4.15 x10-15 eVs or 6.63 x10-34 Js.

What is the frequency of a 70 keV x-ray? Sample problem What is the frequency of a 70 keV x-ray? 1.69 x1019 Hz.

Practice Problem What is the energy of a 960 kHz electromagnetic wave?

Practice Problem What is the frequency of a 86 keV x-ray?

Matter and Energy Law of conservation of matter Law of conservation of energy

Theory of Relativity E = mc2 Where: E = energy in joules m = mass in kg c = velocity of light in m/s 1 Joule = 6.24 x1018 eV

Sample problem What is the energy equivalence of an electron (mass = 9.109 x10-31 kg), as measured in joules and electron volts? 81.972 x10-15 J 51.15 x104 eV

What is the mass equivalence of a 90 keV x-ray? Practice Problem What is the mass equivalence of a 90 keV x-ray?

What is the mass equivalence of a 340-nm photon of UV light? Practice Problem What is the mass equivalence of a 340-nm photon of UV light?