CSIR-NET and GATE physics: Electric and Magnetic fields

CSIR-NET and GATE physics: Electric and Magnetic fields: "We will now discuss electric and magnetic field vectors (E and B)at a point in the absence of charge. Now let us place a charge q at poi..."


1. X-Rays are emitted from metal when metal surface is hit by high energy electrons. The electrons penetrate close to the nucleus and displace electrons around the nucleus. The enerfy change is equal to hf where f is the frequency and is very high for radiation emitted.
2. X-Rays are EM waves of very high frequency and short wavelength near about a 100 times shorter then the wavelength of visible light.
3. Moseley’s law : Moseley measured the frequencies of characteristic X-rays from large number of elements and plotted the square root of th frequency against its position number in the periodic table.
His observations are mathematically expressed as
√(v) = a(Z-b)
v = the frequency of characteristic X-rays from the elements\
Z = atomic number
a, b are constants
Bragg’s law :Atomic structure of crystals can be studied by X Ray analysis and was started in 1914 by Sir William Bragg with notable achievements.
Bragg's law is :- 2d sin θ = n λ
d = interplanar spacing of the crystal on which X-rays are incident
θ = is the incident angle at which X-rays are strongly reflected.
n = 1,2,3 …
λ = wave length of X-rays
Application of Bragg’s law : By using a monochromatic X-ray beam (having a single wave length) and noting the angles of strong reflection, the interplanar spacing d and several information about the structure of the crystals can be obtained.
4. x-rays do not contain charged particles. hence they are not deflected by electric or magnetic field.

5. They effect a photographic plate. The effect is stronger than light.
6. When incident on certain materials barium platinocyanide, X rays cause fluorescence.

7. When passed through a gas, X rays ionize the molecules of the gas.

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