<< Chapter < Page Chapter >> Page >

Electromagnetic spectrum: rules of thumb

Three rules that apply to electromagnetic waves in general are as follows:

  • High-frequency electromagnetic waves are more energetic and are more able to penetrate than low-frequency waves.
  • High-frequency electromagnetic waves can carry more information per unit time than low-frequency waves.
  • The shorter the wavelength of any electromagnetic wave probing a material, the smaller the detail it is possible to resolve.

Note that there are exceptions to these rules of thumb.

Transmission, reflection, and absorption

What happens when an electromagnetic wave impinges on a material? If the material is transparent to the particular frequency, then the wave can largely be transmitted. If the material is opaque to the frequency, then the wave can be totally reflected. The wave can also be absorbed by the material, indicating that there is some interaction between the wave and the material, such as the thermal agitation of molecules.

Of course it is possible to have partial transmission, reflection, and absorption. We normally associate these properties with visible light, but they do apply to all electromagnetic waves. What is not obvious is that something that is transparent to light may be opaque at other frequencies. For example, ordinary glass is transparent to visible light but largely opaque to ultraviolet radiation. Human skin is opaque to visible light—we cannot see through people—but transparent to X-rays.

Radio and tv waves

The broad category of radio waves    is defined to contain any electromagnetic wave produced by currents in wires and circuits. Its name derives from their most common use as a carrier of audio information (i.e., radio). The name is applied to electromagnetic waves of similar frequencies regardless of source. Radio waves from outer space, for example, do not come from alien radio stations. They are created by many astronomical phenomena, and their study has revealed much about nature on the largest scales.

There are many uses for radio waves, and so the category is divided into many subcategories, including microwaves and those electromagnetic waves used for AM and FM radio, cellular telephones, and TV.

The lowest commonly encountered radio frequencies are produced by high-voltage AC power transmission lines at frequencies of 50 or 60 Hz. (See [link] .) These extremely long wavelength electromagnetic waves (about 6000 km!) are one means of energy loss in long-distance power transmission.

A high-voltage traction power line is shown to the side of a roadway. The power line in the photo has two transmission poles supporting the cables.
This high-voltage traction power line running to Eutingen Railway Substation in Germany radiates electromagnetic waves with very long wavelengths. (credit: Zonk43, Wikimedia Commons)

There is an ongoing controversy regarding potential health hazards associated with exposure to these electromagnetic fields ( E size 12{E} {} -fields). Some people suspect that living near such transmission lines may cause a variety of illnesses, including cancer. But demographic data are either inconclusive or simply do not support the hazard theory. Recent reports that have looked at many European and American epidemiological studies have found no increase in risk for cancer due to exposure to E size 12{E} {} -fields.

Questions & Answers

Please i really find it dificult solving equations on physic, can anyone help me out?
Big Reply
what is the equation?
fersnels biprism spectrometer how to determined
Bala Reply
how to study the hall effect to calculate the hall effect coefficient of the given semiconductor have to calculate the carrier density by carrier mobility.
what is the difference between atomic physics and momentum
Nana Reply
find the dimensional equation of work,power,and moment of a force show work?
Emmanuel Reply
What's sup guys
cul and you all
cool you bro
so what is going on here
hello peeps
Michelson Morley experiment
Riya Reply
how are you
am good
Calculate the final velocity attained, when a ball is given a velocity of 2.5m/s, acceleration of 0.67m/s² and reaches its point in 10s. Good luck!!!
Eklu Reply
vf=vi+at vf=2.5+ 0.67*10 vf= 2.5 + 6.7 vf = 9.2
s = vi t +1/2at sq s=58.5 s=v av X t vf= 9.2
how 2.68
v=u+at where v=final velocity u=initial velocity a=acceleration t=time
express your height in Cm
Emmanuel Reply
my project is Sol gel process how to prepare this process pls tell me
the dimension of work and energy is ML2T2 find the unit of work and energy hence drive for work?
Emmanuel Reply
Two bodies P and Quarter each of mass 1000g. Moved in the same direction with speed of 10m/s and 20m/s respectively. Calculate the impulse of P and Q obeying newton's 3rd law of motion
Shimolla Reply
definition for wave?
Doc Reply
A disturbance that travel from one medium to another and without causing permanent change to its displacement
In physics, a wave is a disturbance that transfers energy through matter or space, with little or no associated mass transport (Mass transfer). ... There are two main types ofwaves: mechanical and electromagnetic. Mechanicalwaves propagate through a physical matter, whose substance is being deformed
thanks jare
Note: LINEAR MOMENTUM Linear momentum is defined as the product of a system’s mass multiplied by its velocity: size 12{p=mv} {}
what is physic
zalmia Reply
please gave me answar
Study of matter and energy
physics is the science of matter and energy and their interactions
physics is the technology behind air and matter
hi sir
how easy to understanding physics sir
Easy to learn
31. Calculate the initial (from rest) acceleration of a proton in a 5.00×106 N/C electric field (such as created by a research Van de Graaff). Explicitly show how you follow the steps in the Problem-Solving Strategy for electrostatics.
Catina Reply
A tennis ball is projected at an angle and attains a range of 78. if the velocity is 30metres per second, calculate the angle
what friction
Wisdom Reply
question on friction
the rubbing of one object or surface against another.
momentum is the product of mass and it's velocity.
what are bioelements?
Friction is a force that exist between two objects in contact. e.g. friction between road and car tires.
With regards to a shielded cable, is there an induced current on the shield when the center conductor is carrying an AC Current? What is the formula?
John Reply
what is phenomena
remilekun Reply
no idea
its phenomenon, an observable fact.

Get the best College physics course in your pocket!

Source:  OpenStax, College physics. OpenStax CNX. Jul 27, 2015 Download for free at http://legacy.cnx.org/content/col11406/1.9
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'College physics' conversation and receive update notifications?