How are X-rays made

The transfer or conversion of energy is always associated with the emission of electromagnetic waves. We met this concept in its simplest form in Chapter 2, when we looked at the transfer of infrared radiation (i.e. heat). This emission of photons occurs because all objects contain electrically charged particles and, whenever an electrically charged particles accelerates, it emits electromagnetic waves. 

All objects at temperatures above absolute zero contain some thermal energy, so electrically charged particles within them continually undergo thermal motion. If we could cool matter to 0 K, then the thermal motion would cease and the matter would not emit any radiation. Again, we saw this idea in Chapter 2. 

But absolute zero is unattainable, so all particles move. Furthermore, the particles never retain an invariant speed because inelastic collisions cause some particles to decelerate and others to accelerate. As a result, everything emits some electromagnetic waves, even if merely in the context of a dynamic thermal equilibrium with the object exchanging energy with its surroundings. 

We simplify the argument here in fact, the energy E of the photon relates to the frequency v of the photon and also the work function j of the metal, according to the equation E = hv — (j . 

The word gradient here implies the slope of a graph of particle velocity (as y ) against time (as x ). 

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