X rays are waves of electromagnetic
energy which behave
in much the same way as light rays, but at wavelengths approximately 1000 times
shorter than the wavelength of light. X rays can pass uninterrupted through
low-densitysubstances such as tissue, whereas higher-density targets reflect or
absorb the X rays because there is less space between the atoms for the short
waves to pass through. Thus, an x ray image shows dark areas where the rays
traveledcompletely through the target (such as with flesh) and light areas
where therays were blocked by dense material (such as bone).
a cathode-ray tube emitted certain invisible rays that could
penetrate paper and wood and, the first person in the world to see through
human flesh, even saw a perfectly clear outline of the bones in his own hand.
The most important application of the x ray, however, was in
medicine, Modern medical x-ray machines are grouped into two
categories: "hard" or "soft" x rays. Soft x rays, which
operate at a relatively low frequency, are usedto image bones and internal
organs and, unless repeated excessively, cause little tissue damage. Hard x
rays, very high frequencies designed to destroy molecules within specific cells
thus destroying tissue, are used in radiotherapy, particularly in the treatment
of cancer. The high voltage necessary to generate hard x rays is usually
produced using cyclotrons or synchrotrons….
JOINTS AND BONES
Practise good posture and healthy habits, to avoid unnecessary stress to bones and joints:Always sit with both feet on the floor or foot rail.Always stand on both feet, distributing the weight and stress evenly.Keep your back straight; never remain stooped over while working or studying. If needed, bring the table up, or get a lower chair so you do not stoop.Lift and carry lighter loads. It is better to take multiple trips, than to lift or carry unnecessarily heavy loads at once.Carry things on both shoulders, and make sure your backpack straps are even so that both shoulders are level.Keep the head level; avoid holding the head bent forward nor to one side.Sleep on pillows of the appropriate height, so that the back is straight while you sleep.Avoid sitting, standing, or lying with the back arched.Forbear from pulling at fingers to crack the joints.Wear comfortable, loose clothes.Avoid sitting on the spinal column or tail bone.Sit on the hip and leg bones with adequate back support and proper height alignment to a counter, table or desk.
rthritis is a category of rheumatic diseases.Arheumatic diseases may cause pain, stiffness, and swelling in the joints, muscles, tendons, ligaments, and bones