Geophysics and Medical Physics

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GEOPHYSICS AND MEDICAL PHYSICS VOLCANO: The interior of the earth is at a high temperature of about 50000C.At this temperature the rock and minerals will be in molten form and they are called Lava. Due to the high temperature, pressure builds up and when the pressure is large enough, the molten lava erupts through the volcano. Thus volcano serves as opening of safety valve as in a pressure cooker. After volcano, the pressure inside the earth decrease and this causes change in interior structure
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  GEOPHYSICS AND MEDICAL PHYSICSVOLCANO: The interior of the earth is at a high temperature of about 5000 0 C.At this temperature therock and minerals will be in molten form and they are called Lava. Due to the hightemperature, pressure builds up and when the pressure is large enough, the molten lavaerupts through the volcano. Thus volcano serves as opening of safety valve as in a pressurecooker.After volcano, the pressure inside the earth decrease and this causes change in interiorstructureEARTH QUAKEThe surface of the earth is made up of layers of rocks called tectonic plates. Due to changein the interior structure of the earth, the plates start moving. This is due to change inpressure and temperature. When a plate moves, the earth above it slides vertically down.This causes the seismic waves on the surface of the earth. The amplitude of the wave ismeasured using an instrument called seismograph. Thus seismograph measures the intensityof earth quake.Unit of Earth quake:The intensity of earth quake is measured in Ritcherscale.This unit is defined asR= log 10 (A)Where A is the amplitude of vertical vibration in micrometer.IfA=1 micro meter, R= 0This 1 µm vibration can be due to motion of a lorry or a train.If A =1 m = 10 6 µm, R = 6Thus R=0 is generally allowed R=6 can be disastrous.During tsunami (Dec 2004), R=9.this includes A= 1km.(Tsunami –Tidal waves)  The sea bed was lifted by 1km upward which caused Tidal waves. Tsunami can be caused bythree reasons1. When meteors fall into the sea2. When volcano eruption occurs under the sea3. When Earthquake occurs at seabed. RAINFALL UNIT  Rainfall is measured as volume of water collected per unit area.Unit of Rainfall == height.Consider a vessel of mouth area a, exposed to rainfall. If V is the volume of water collected,thenAmount of Rainfall =V/A in cm PROBLEM: A mug of mouth area 100cm 2 is exposed to rainfall. If collected one liter of rain waterduring a rainfall, calculate the amount of rainfall in that regionRainfall = V/A = 1000/100 = 10cm LIGHTNING ARRESTOR The charge density in a metal is proportional to its curvature. Sharp points are more curvedand therefore at sharp points, charge density is minimum i.e. sharp points can accommodatemore charges.Lightning is caused when a positively charged cloud collides with a negatively charged cloud.This causes lightning and thunder. To avoid lightning affecting our buildings, we use lightningarrestor, which is metal rod with sharp ends facing the sky. Lightning arrestor is placed at Obj100   Obj101Obj102   Obj103  the top of a tall building. This attracts the charged clouds and the charges are grounded inthe earth using thick conducting wire, like copper.Lightning arrestors provide safety for the building and also for the neighboring area. Whenthere is no lightning arrestor as in a village, the tallest tree will attract the charges fromthe clouds. For this reason one should avoid standing under a tree during lightning. COSMIC SHOWERS: Cosmic means outer space. Cosmic rays are those emerging from the outer space. Theelectromagnetic radiation from the outer space interacts with the atmosphere of the earthand charged particles are produced. These particles enter the earth as showers, which arecalled cosmic shower.The cosmic shower approaches earth from all directions. The cosmic shower enters theNorth Pole (N) and South Pole (s) of the Earth.Near the Equator the charged particles cannot enter as they will be deflected in circularpath (see fig)  The deflection of charged particles is due to earth’s magnetic field. This region is called VanAllen belt. This belt provides protection for animals and plant life. In the north and southpoles, there is no such protection and so animals and plants are scarce in Polar Regions. COLIDGE TUBE; Coolidge tube is an apparatus for producing X-rays. PRINCIPLE :When fast moving electrons hit a metal target-rays are liberated. APPARATUS: The figure shows a Coolidge tube. The filament emits electrons and they are acceleratedtowards the positive potential. When the electrons hit the metal target-rays are generated.The wave length of X-ray is about 1 AU (one angstrom unit) (1 AU=10 -10 m) the wavelengthdepends on the applied high voltage. When the voltage is low, we get soft x-rays. When thevoltage is high, we get Hard X-rays. The hard X-ray is used for scientific purpose andindustrial applications. The soft X-rays for medical applications. PROPERTIES OF X-RAYS: 1. It has velocity of light (3 x 10 8 m/s)
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