The Generation of Electromagnetic Waves

James Clerk Maxwell

summarized the connection between electricity and magnetism via a set of equations; unified them with the physics of light by discovering that light is an electromagnetic wave

Maxwell’s equations

first one is Gauss’s law, second equation is similar to the first but applies to magnetic fields, third one is Faraday’s law, fourth is Ampere’s law

Faraday’s law

says a changing magnetic field gives rise to an electric field

Ampere’s law

says than a changing electric field gives rise to a magnetic field

Maxwell’s displacement current

final term in the fourth of Maxwell’s equations, refers to changing electric field between the plates of a discharging capacitor

Electromagnetic wave

created by the combined effects of the oscillating electric and magnetic fields

Speed of light

3×10⁸ m/s

Wave

how we describe the transference of energy through a substance without any of the substance itself being transported

Longitudinal wave

wave in which the the components of the material move back and forth in the same direction as the wave

Transverse wave

wave in which the direction of vibration is perpendicular to the direction of the wave

Wavelength

horizontal length between repeating cycles of a wave

Amplitude

maximum height of vibration, intensity of the wave

Wave frequency

how many full wavelengths pass through a given point per second, measured in hertz

Hertz

1 hertz=1 wavelength/second

Velocity of a wave

v=λf

Speed of sound

300 m/s

Sound vs light

sound is slower, cannot travel through the vacuum of space; light is a million times faster than sound, can travel through the vacuum of space

Wavelength of a light wave

λ=c/f

Frequency of a light wave

f=c/λ

Visible Spectrum

400-700 nanometers

Infrared radiation

longer in wavelength and lower in frequency than red, can be felt as heat

Microwave/radio wave

used in long-distance communication

Microwave ovens

has a mini particle accelerator that causes electrons to emit microwave radiation, metal mesh prevents microwaves from escaping

Ultraviolet radiation

higher in frequency and short in wavelength than violet, energetic enough to break apart skin cells

X-rays

can penetrate many materials due to their small size

Wilhem Rontgen

found that X-rays are emitted by electrons accelerated by high voltages, took the first X-ray photograph of his wife’s hand

Gamma rays

have the highest frequency and shortest wavelength, come from atomic nuclei undergoing radioactive decay

Ionizing radiation

UV and beyond, capable of breaking apart atoms in the human body