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Homework Help: How are electricity and magnetism related?

  1. May 5, 2007 #1
    I know that electric fields generate magnetic fields (when you put a compass next to a wire that has current in it the needle moves indicating that a mag. field is present). I know that changing magnetic fields can generate electric fields or induced emf.

    What does electromagnetic waves have to do with this though? It says in my textbook that whenever a charged particle accelerates it radiates energy. Why is this? So the EM waves are actually a combination of magnetic and electric fields?
  2. jcsd
  3. May 5, 2007 #2
    Alright, now I've read about how alternating electric fields generate waves and I know that alternating electric fields will create alternating magnetic fields and the alternating magnetic fields will geneterate its own wave perpendicular to the electric wave. These waves created by the fields are just energy right? All waves are propagations of energy correct? Is there like a mathematical formula to cancel out the units of the electric field and the magnetic field to get Joules? I'm just astonished at how a wave can form from varying fields of electricity and magnetism.
  4. May 5, 2007 #3
    electricity and magnetism are related in that the magnetic force is merely the electric force in another inertial reference frame.
  5. May 5, 2007 #4
    Youre looking for the equation E=hf. An EM waves energy equals its frequency times Planks constant. This provided evidence for the photon theory and the wave-particle nature of light
  6. May 5, 2007 #5
    Is that means that a charged particles (mass) annihilate at some time when they radiate all of their energy?
  7. May 5, 2007 #6
    Not usually. The most obvious example of E=hf is an atom absorbing a photon of light, an electron jumping up to a higher energy level, the electron dropping back down to a lower energy level, and emitting a photon. The change in energy is proportional to the frequency of light used, and the only absorbable frequencies are those that correspond to the atoms specific energy levels.

    However, when a particle encounters its respective antiparticle (an electron and a positron), the 2 annhilate each other. The mass is converted to energy (E=mc^2) and photons are created of frequency E/h

    Mass doesnt usually just turn into energy though. Electrons in an atom are not classical particles. They are orbiting the nucleus and should be constantly giving off energy, but they only do so when they drop to a lower orbital
  8. May 5, 2007 #7
    I was kind of talking about an electron or proton on its own.
    Like there is a single electron(or a proton), traveling in space @ some speed. So, it is generating a magnetic field (right?). And let's say this magnetic force do work on a particle.
    So, that means that moving electron or proton has lost some energy equals to the work done on the particle.

    So, from where does that energy comes from? I am thinking right now that the moving proton or electron would lose its kinetic energy rather than getting its mass converted to energy.
    Am I right though?

  9. May 6, 2007 #8
    When a magnetic field exerts a force on a moving charge, the force is perpendicular to the velocity and the field (right hand rule). In this case, the work done on the particle is zero because force is perpendicular to displacement. Im not sure about the other case where a magnet does work on another stationary magnet
  10. May 6, 2007 #9
    That does make sense!
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