Electromagnetic Energy

Prepared by: Timothy John D. Matoy

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.

Photons

Late in 19th century.

Showed that visible light has both electric and magnetic properties, hence the term electromagnetic energy.

James Clerk Maxwell

It can travel through empty space.

It travels with the speed of light.

It travels in a wave-like fashion.

Properties of EM Radiation

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

Velocity

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.

Wavelength

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

Frequency

V = λf

Velocity = wavelength x frequency

Wave Equation

C = λf

Speed of light = wavelength x frequency

Electromagnetic Wave Equation

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?

Practice 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?

Sample problem

The frequency range of electromagnetic energy extends from approximately 102 to 1024 Hz.

The wavelength are approximately 107 to 10-16 m.

Electromagnetic Spectrum

Electromagnetic Spectrum

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

Visible light

Relatively low energy and relatively very long wavelength

Radiofrequency

Gamma rayX-ray

Ionizing Radiation

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.

Wave-Particle Duality

“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

Quantum Theory

E = hf

Where:E = photon energyh = Planck’s constantf = photon frequency

Planck’s Quantum Equation

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

The Constant of Proportionality

What is the frequency of a 70 keV x-ray?

Sample problem

What is the energy of a 960 kHz electromagnetic wave?

Practice Problem

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

Practice Problem

Law of conservation of matter

Law of conservation of energy

Matter and Energy

E = mc2

Where:E = energy in joulesm = mass in kgc = velocity of light in m/s

1 Joule = 6.24 x1018 eV

Theory of Relativity

What is the energy equivalence of an electron (mass = 9.109 x10-31 kg), as measured in joules and electron volts?

Sample problem

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

Practice Problem

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

Practice Problem