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11.
They have injurious effect on human bodies. Exposure of human body to X-rays causes reddening of the skin. The long exposures result into surface sores.
12.
When X-rays fall on certain metals, secondary X-rays are produced, which are characteristic rays of the metal. The secondary X-rays are accompanied by fast moving electrons. 60. Text Book of Physics, op cit., pp. 97-98
"This discussion shows that, at a point where an electromagnetic wave is passing, the electric and the magnetic field vectors oscillate in phase along mutually perpendicular directions, and are both located in a plane which is perpendicular to the direction of prepagation of the wave. To be more specific, these oscillations have the following meaning. If at any point at a specific time, the E and B vectors have zero values, their values will increase with the time along two mutually perpendicular directions, then reach their maximum values simultaneously and start decreasing; again reaching zero. Then they reverse their directions, reach their maxima and again decrease. This way the field vectors oscillate along mutually perpendicular directions, remaining confined to a plane which is perpendicular to the direction of the electromagnetic wave, so long as the wave is propagated through that point.
It should also be noted that in this process, the kinetic energy of the charge oscillating between the two spheres is radiated away in the form of the energy of electromagnetic radiation, which propagates in the space. The frequency of the waves generated is the same as the frequency of the oscillation of charge between the spheres. The expression c (velocity) λ (wavelength) xf (frequency) holds true. Thus, if one wants to generate waves of 300 meter wavelength, the frequency of oscillations should be
λ = 300 =
Jain Educationa International
300 × 106 f
Seven years after the experiments by Hertz, Jagdishchandra Bose produced electromagnetic waves in the range of wavelength 5 mm to 25 mm. Around the same time an Italian Scientist Marconi succeeded in sending and receiving electromagnetic waves over a distance of several miles.
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