What is Electomagnetic: Definition and 26 Discussions

The electromagnetic spectrum is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energies.
The electromagnetic spectrum covers electromagnetic waves with frequencies ranging from below one hertz to above 1025 hertz, corresponding to wavelengths from thousands of kilometers down to a fraction of the size of an atomic nucleus. This frequency range is divided into separate bands, and the electromagnetic waves within each frequency band are called by different names; beginning at the low frequency (long wavelength) end of the spectrum these are: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays at the high-frequency (short wavelength) end. The electromagnetic waves in each of these bands have different characteristics, such as how they are produced, how they interact with matter, and their practical applications. The limit for long wavelengths is the size of the universe itself, while it is thought that the short wavelength limit is in the vicinity of the Planck length. Gamma rays, X-rays, and high ultraviolet are classified as ionizing radiation as their photons have enough energy to ionize atoms, causing chemical reactions.
In most of the frequency bands above, a technique called spectroscopy can be used to physically separate waves of different frequencies, producing a spectrum showing the constituent frequencies. Spectroscopy is used to study the interactions of electromagnetic waves with matter. Other technological uses are described under electromagnetic radiation.

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  1. S

    B Inductive Reactance of Solenoid with Solid Metal Core With respect to frquency

    Hi. Consider the Solenoid/Inductor Like one the Picture. There is Air gap between the coil and inserted solid metal. Hi. Consider the Solenoid/Inductor Like one the Picture. There is Air gap between the coil and inserted solid metal. The solid metal is from Aluminum or Copper (Both have...
  2. abdulbadii

    I Outright understanding L/R inductor time constant

    How is the real understanding, when an external constant E potential (voltage) is imposed/applied on a LR circuit, that is being charged as the characteristic L/R inductor time constant: the greater R the shorter time inductor get (full) charged This absolutely independent to the E; it could...
  3. C

    I Understanding the critic of this author for conventional S field

    I joined an article by Davis and Onoochin. I have troubles to understanding his critic of the conventional field momentum interpretation (sec. 3). More precisely, while I am able to check that eq. (23) is true, and that the field is of the order ##1/r^5##, I don't understand in which way this...
  4. janjan

    I Measurement of charge in motion

    In Purcell's E&M Section5.3 "Measurement of charge in motion", he said when a charge is in motion, the force on test charges may not be in the direction of radius vector r. And in next paragraph, he defined Q by averaging over all directions. However, he just measured the radial component of...
  5. Anne Ross

    Hi I’m Anne and I’m interested in the physics of the brain

    I am interested in consciousness and it’s material basis - in the brain, we presume! I’m interested in whether or not part of the electromagnetic field of the brain is consciousness as claimed by Susan Pocket and various others. She claims that the conscious qualities we see such as a red car...
  6. chandrahas

    B Containing a plasma with a oscillating cusp?

    I've recently learned that conductors can achieve stability when placed in an alternating electric field. This is because of Lenz's law. So I was wondering if we could levitate a conductor and stabilize it, can we do the same thing with a plasma? If we can create a magnetic cusp, but oscillate...
  7. B

    Determine a cable core diameter for RF current carrying loop

    Basic Question Alert ! (I need to brush up my basics and need your help) Problem Statement: I wish to make a current carring cable loop to generate a controlled magnetic field. http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/curloo.html As I understand, the magnetic field generated depends...
  8. H

    Why do we need a switch before a relay?

    So in high current circuits which involve say a starter motor in a car we need a starter relay since a normal switch cannot handle the high current flow. I think the reason I'm asking this question is because I don't understand what exactly makes the relay be able to handle the current unlike...
  9. Toby_phys

    The slowing down of a Farady disc

    Homework Statement A homopolar generator consists of a metal disc of radius ##a## and a central axle which has radius ##a/4##. The disc has resistivity ##\rho## and thickness ##t##. It is rotated in a uniform magnetic field ##B## about an axis through the centre, which is parallel to ##B## and...
  10. B

    Electromagnetic Levitation for a stationary hoverboard - How can I do it?

    I am University Student currently working on a project to make a stationary hover board. This is just a prototype and does not need to support a human and only needs to support about 1kg but with as much "lift" or distance between the magnets as possible - (100mm?) Ideally we want to be able to...
  11. cluelessGUY

    Magnet clamp repelling in coil

    I have a practical question. I want to make a rubber (silicone) hose/plug that is pinched closed by two magnets ( very strong magnets such as ones from a hard drive the Neodymium kind). I want to place then into a coil and when I want the liquid to flow, I want to turn on the coil and have the...
  12. L

    I Electromagnetic Force in Special Relativity

    Hi! I came out with a problem last night I wasn't able to solve: Let's assume we have a condensator with a uniform electric field E confined in its inside, lying on the z axes. Let's also assume we have a piece of a ferromagnetic object aligned with the condensator at time t = 0, on the y-axes...
  13. Alvis

    Not a homwork problem, Fresnel Equations

    Homework Statement I was just curious, I know you can derive the critical angle using Snell's law..but could you use it using the Fresnel Equations of reflection, both of them? Homework Equations |r|=1 internal reflection of light...
  14. A

    ANSYS System Coupling: Mechanical-Electrical Inquiry

    I have an inquiry about how to make a system coupling between mechanical and electrical system in ANSYS program.
  15. F

    Maxwell's equation has well defined divergence?

    Homework Statement How to I explain that maxwell's equation has well defined divergence Homework Equations All four EM Maxwell's equation The Attempt at a Solution I discussed it by showing one of the property of Maxwell's equation that is the Divergence of a Gradient is always zero (With...
  16. J

    When can I use Helmholtz equation for electromagnetics

    The complete Maxwell wave equation for electromagnetic field using the double curl operator "∇×∇×". Only when the transverse condition is hold, this operator can equal to the Laplace operator and form the helmholtz. My question is what's the condition can we use the helmoltz equation instead of...
  17. Ryan Reed

    How does the EM force transmit charge information?

    If photons are the force carrier of the EM force, and they have no charge, how do they give the information between two charged particles? How would a proton know the difference between a electron and positron?
  18. Maximtopsecret

    Lorentz transormation for electomagnetic field

    Homework Statement In laboratory's frame the angle between vectors E and H is given φ. Find the frame where these vectors will be parallel. Homework Equations The Attempt at a Solution I suppose I should require equal angle between each of the E' and H' and axes in the ''new'' frame. Means...
  19. O

    Radar antenna: measuring H or E?

    Hi there, Maybe this is a stupid question. Maybe not. I want to make a statement in my thesis that says that all radar antennas on satellites derive the EM field by: receiving the time-varying H field, and from the induced current derive the EM field. Am I correct in saying that? Or are there...
  20. R

    Electromagnetic induction of a wire in a complete circuit

    Say for you had a wire in a complete circuit inside a magnetic field (pointing inwards) perpendicular to the wire. You move the wire across (to the right) , cutting lines of flux, this induces a current in the wire. The induced current acts upwards using the dynamo rule (thumb is motion...
  21. amjad-sh

    Electomagnetic oscillation in lc circuit

    Hi, We know that when we connect a charged capacitor to a coil, the capacitor will discharge in the coil that means that the current will flow in the circuit in decreasing manner with respect to time .So an emf will be created in a way that oppose the decrease. Bin will has the same...
  22. D

    Electomagnetic wave frequency and photons

    If i calculate the frequency of light with λ = 600nm ... Frequency (v) = c/λ = 49.9654 x 1012 Hz (waves per second) Can i say this is the frequency of photons i.e. 49.9654 x 1012 Hz (waves per second) Thanks DD
  23. M

    Faraday's law of electomagnetic induction

    A piece of copper wire is formed into a single circular loop of radius 13 cm. A magnetic field is oriented parallel to the normal to the loop, and it increases from 0 to 0.60 T in a time of 0.45 s. The wire has a resistance per unit length of 3.3 x 10-2 ohm/m. What is the average electrical...
  24. P

    Electromagnetic Waves: Wave Length & X-Rays vs Microwaves

    just working on some problems and wondering if anyone could help, it's about wavelength (radiation waves), I just need to make sure that x-rays are smaller than microwaves..I keep looking over my notes and need this one part if anyone could just let me know that I have this fact straight so I...
  25. L

    What happens when a magnetized strip is moved past a coil of wire?

    When a strip of magnetic material, variably magnetized, is embedded in a plastic card that is moved past a small coil of wire, what happens in the coil. What is a practical application of this? I have no idea what this means, I don't understand Physics and my teacher doesn't help either. He...
  26. E

    Electromagnetic Waves: What & Why

    What are electromagnetic waves? Why are they so important? Thanks in advance