Name: Moseley’s Law
Uploaded: 2019-07-19
Duration: 7 min 40 s
Description: Moseley’s law is an empirical law concerning the characteristic x-rays that are emitted by atoms. Let's watch this video to learn about Moseley's law.

Question

Draw a labelled diagram of a Coolidge tube and explain the origin of X-rays. What is the relation between the minimum wavelength of the continuous spectrum and the voltage applied across the X-ray tube? Give necessary formula.

Accepted Answer

The basic shape of the original Coolidge tube consisted of a spherical bulb with two cylindrical arms extending out on opposite sides

As the cathode filament is heated, it emits electrons. These electrons are accelerated towards the positively charged anode and when the electrons strike the anode, they change direction and emit x-rays with a continuous range of energies. The maximum energy of the x-rays is the same as the kinetic energy of the electrons striking the anode.

The intensity of the x-ray can be controlled by changing the filament current. Higher the accelerating potential, the smaller the wavelength of x-ray produced. Hence, greater is the penetrating power.

The high energy electrons get decelerated by Coulomb’s interaction with the target atom. These decelerating electrons emit continuous X-rays (or bremsstrahlung). When an electron loses its entire energy in a single Coulomb's interaction then X-rays of minimum wavelength (cut-off wavelength) are emitted.

The cut-off wavelength or maximum energy (frequency)of the continuous X-ray spectrum is $K_{0} = {hν}_{\max} = \frac{hc}{λ_{\min .}}$

Or $λ_{\min} = \frac{hc}{K_{0}} or \frac{hc}{eV}$ , where $V$ = accelerating voltage between the anode and cathode, BY putting the values, we have

$λmin = \frac{12375}{V}$

Draw a labelled diagram of a Coolidge tube and explain the origin of X-rays. What is the relation between the minimum wavelength of the continuous spectrum and the voltage applied across the X-ray tube? Give necessary formula.

Important Questions on X-Rays

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