Medical x-rays provide images of the body but utilize radiation that in large doses can damage cells. A completely different technology, magnetic resonance imaging (MRI), emerged in the late 1970s. It produces highly detailed images of soft tissues and requires no x-radiation. MRI is based on nuclear magnetic resonance, a technique developed to probe molecular structure. Ironically, public anxiety about radioactivity and nuclear energy kept the word “nuclear” out of the name of this new kind of imaging, which otherwise might have been called NMRI (nuclear magnetic resonance imaging). Precessing Protons:To understand the MRI, let’s think about a molecule that contains hydrogen, like a molecule of water or fat. The nuclei of these hydrogen atoms are protons. Each proton possesses an intrinsic spin, so that it acts much like a spinning top. Now suppose we put the molecule between the pole-pieces of a magnet, so the protons are in a magnetic field. Each proton now turns around the field direction like a little gyroscope. (See diagram.) This motion is called precession.As they precess, the protons, according to quantum mechanics, can have only two orientations. Because of the magnetic field, these two orientations correspond to slightly different energies. If we shine radio waves on these protons, and the radio waves have just the right frequency, the lower energy protons can absorb photons of radiation and flip over. (Quantum mechanics tells us that the photon’s energy is proportional to its frequency.) By observing the details of this energy absorption, which depend on the environment of the protons, we can figure out, for example, if the protons are in water or in fat. If we analyze many such measurements, we can get an image of a “slice” of the body, as shown. Notice the detail can be seen in the soft tissues. MRI images can show features as small as 1 mm.

Sun's rays are considered as coming parallel to the earth because the size of the Sun is over 200 times to the size of the earth. The diameter of the sun is about 830,000 miles and  they distance to the sun is about 93,000,000 miles.
One more interesting phenomenon :sun's rays between clouds spread in many directions, making the sun appear as if it's just behind the clouds .The spreading  effect makes parallel lines appear to meet at a distance. Due to the same reason  the parallal railway tracks appear to converge at far off point.The rays coming from the sun can be assumed to be like the railway tracks, except that the rails are much farther apart,  because light rays from the sun cover the whole Earth. That means as you stand between the rays looking toward the sun, the beams will appear to radiate out from a point in front of you to positions o­n either side of you

We know that the temperature of a liquid do not increase when it start boiling.The heat suppied to the liquid is utilised in evaporating the liquid.Please keep in mind that we are not talking about increase in boiling point with increase in pressure.(pressure cooker).We are interested in boiling a liquid at existing pressure.

If heated uniformly throughout,A liquid can be heated to a temperature higher than its boiling point (at existing pressure) and this phenomenon is known as superheating.This phenomenon can be easily observed while heating water inside a Microwave oven.