Wednesday, June 30, 2010

General science PHYSICS-1

PHYSICS

PRESSURE
  1. Units
    • atmosphere, technical atmosphere
    • mm, cm, inches of mercury
    • mm, cm, inch, foot of water
    • kip, ton-force, pound-force
    • pound per square inch
    • bar, decibar, millibar
    • barye, dyne
    • sthene per square metre, pieze
  2. Pressure in everyday life
    • Transpirational pull in plants (negative pressure caused by surface tension), used to suction water from the water to leaves
    • Casimir effect: physical force betwen two uncharged metal plates in vaccuum. Used in nanotechnology
    • Atmospheric pressure decreases with elevation. Due to this boiling point of water decreases with elevation
    • Blood pressure is the pressure exerted by circulating blood on the walls of blood vessels. For a healthy adult human the pressure should be 115 mm Hg (systolic) and 75 mm Hg (diastolic)
    • A microphone works on the principle of sound pressure. A thin membrane converts sound pressure into an electrical signal
    • Caisson Disease (aka The Bends or Decompression Sickness) occurs due to sudden change in atmospheric pressure. It happens when a person moves from a high pressure environment to a low pressure. Examples include divers returning from depth, workers in caissons during bridge construction, sudden drop in aircraft pressure etc. Can lead to paralysis and death.
    • Vaccuum is a volume of space where pressure is less than atmospheric pressure. Examples include vaccuum cleaners, deep space, incandescent light bulb
GRAVITATION
  1. History of gravitational theory
    • 4th century BCE: Aristotle proposed heavy bodies are attracted towards the center of the universe due to an inner gravitas
    • 628 CE: Brahmagupta recognized a force of attraction. He followed the Heliocentric solar system and propsed gravitational attraction between the Sun and the Earth
    • 1660s: Robert Hooke explains celestial gravity
    • 1687: Isaac Newton proposes law of universal gravitation
    • 1915: Albert Einstein proposes theory of general relativity
  2. Gravitation in everyday life

    : Physics

    Notes

    Speed is the rate of change of distance
    speed = \frac{distance}{time}
    Velocity is the rate of change of displacement. It signifies both the speed and the direction of movement of an object.
    velocity = \frac{displacement}{time}
    Acceleration is the rate of change of velocity.
    acceleration = \frac{velocity}{time}
    Acceleration due to gravity is the acceleration experienced by an object as it falls freely towards the ground. It is constant throughout the surface of the earth.
    g= 9.8 \frac{m}{s^2}
    Momentum is a measure of the quantity of motion possessed by a body.
    momentum = mass * velocity
    Equations of motion
    Let an object be moving for time t at an acceleration a resulting in a displacement s. If the initial velocity of the object is u and the final velocity v, the following equations hold true
    v=u + at
    s = ut + \frac{at^2}{2}
    v^2 - u^2 = 2as
    Newton’s laws of motion
    First law: A body continues in its state of rest or uniform motion unless compelled to change by an unbalanced force
    Second law: A body of mass m under an acceleration a experiences a force F given by F = ma
    Third law: Whenever a body A exerts a force F on another body B, the second body B exerts force -F on A.

    Questions

    1. The universal law of motion was propounded by
      1. Kepler
      2. Galileo
      3. Newton
      4. Copernicus
    2. The gravitational force with which the Sun attracts the Earth is
      1. less than the force with which the Earth attracts the Sun
      2. the same as the force with which the Earth attracts the Sun
      3. more than the force with which the Earth attracts the Sun
      4. constant throughout the year
    3. The mass of a body is different from its weight.
      1. Mass is variable whereas the weight is constant
      2. Mass varies very little at different places whereas weight varies significantly
      3. Mass is constant but weight increases from the pole to the equator
      4. mass is a measure of quantity of matter whereas weight is a force
    4. The weight of a body is
      1. same everywhere on the surface of the earth
      2. maximum at the poles
      3. maximum at the equator
      4. more on hills than in plains
    5. If a body is taken from the Earth to the Moon,
      1. its mass will be different but weight will still be the same
      2. both mass and weight will be different
      3. mass will be the same but weight will be different
      4. mass and weight will both remain unchanged

        PHYSICS: NON-INVASIVE IMAGING

        Overview

      5. Medical imaging is the technique and process used to create images of the human body for medical purposes
      6. Non-invasive imaging is the method of producing images of internal tissues without surgical procedures
      7. Non invasive imaging techniques can be used to produce anatomical assessment of tissues (such as X-rays) as well as functional assessments (such as MRI)
      8. As a discipline, it includes radiology, nuclear medicine, endoscopy, thermography etc
      9. Non-invasive imaging is a vast field with differing technologies such as X-rays, tomography, MRI etc
      10. Non-invasive imaging provide highly valuable diagnostic tools for diagnosing and treating varied ailments such as cancer, fractures, etc
      11. Imaging technologies can be broadly classified into two categories
        • Anatomical imaging modalities: these imaging techniques provide information on the anatomy i.e. the physical structure of the organ/tissue under study
        • Functional imaging modalities: these imaging techniques provide information on the physiological functioning of the organ/tissue under study
      X-RAYS

    6. X-rays were discovered by Wilhem Conrad Rontgen (Germany) in 1895. He won the Nobel in Physics 1901
    7. Radiography is the imaging process that uses X-rays to capture images
    8. In conventional radiography, X-rays from a X-ray tube pass through the patient and are captured by an X-ray sensitive film screen
    9. Nowadays, digital radiography (DR) is becoming popular, in which x-rays strike an array of sensors that convert the signal to digital mode and displays the images on a computer screen
    10. X-rays are the preferred diagnostic tool for studying lungs, heart and skeleton (including fractures) due to their simplicity, available and low cost
    11. X-rays is an anatomical imaging technology
    Fluoroscopy

    • Fluoroscopy is used to obtain real time moving images of the internal structures
    • Fluoroscope systems consist of an X-ray source and a fluorescent screen connected to a closed circuit TV. The patient is position between the source and the screen
    • Fluoroscopes use low x-ray radiation doses
    • Fluoroscopy also involves use of radiocontrast agents that increase the contrast of a specific tissue w.r.t. surrounding tissues by strongly absorbing or scattering the x-rays
    • The radiocontrast agents enable visualization of dynamic processes such as peristalsis in the digestive tract of blood flow in arteries and veins
    • Commonly used contrast agents include Barium and Iodine. These may be administered orally or rectally or injected into the blood stream
    • Used mainly for investigating gastrointestinal functions, orthopaedic surgery and urological surgery
    • Fluoroscopy is a functional imaging technology
    Computed Tomography (CT)

    • Computed Tomography uses X-rays in conjunction with software algorithms to image the body
    • CT generates a three-dimensional image of an object using a large series of X-ray images taken around a single axis of rotation
    • CT produces a volume data which can be manipulated in order to demonstrate various body functions
    • Compared to traditional radiography, CT produces 3d information and has much higher contrast and resolution, but also uses much higher doses of radiation
    • CT scanners were first developed by Sir Godfrey Hounsfield (Britain) in 1972. He won Nobel in Medicine in 1979
    • CT is used primarily for detecting cerebral haemorrhage, pulmonary embolism, aortic dissection, appendicitis and kidney stones
    • CT is an anatomical imaging technology
    Ultrasound

    • Ultrasound was first developed for medical use by John Wild (Britain) in 1949
    • Ultrasonography uses ultrasound (high frequency sound waves) to visualize soft tissues in the body in real time
    • Ultrasound does not involve any ionizing radiation, hence it considered safer than X-rays or CT and is used for obstetrical imaging
    • Ultrasound is limited by its inability to image through air or bone, and by the skill of the examiner
    • Ultrasound is used primarily to study the development of foetus
    • A variant of ultrasound, the colour flow Doppler ultrasound is used in cardiology for diagnosing peripheral vascular disease
    • Ultrasound is a functional imaging technology
    Magnetic Resonance Imaging (MRI)

    • MRI was invented by Paul Lauterbur (USA) and Sir Peter Mansfield (Britain) in the 1970s. They won Nobel in Medicine in 2003
    • MRI uses strong magnetic fields to align atomic nuclei within body tissues, and then uses a radio signal to disturb this alignment and observes the signals generated as the atoms return to their original states
    • The working principle of MRI is called Nuclear Magnetic Resonance (NMR)
    • MRI scans give the best soft tissue contrast of all imaging modalities
    • MRI does not use any ionizing radiation. However, it does use powerful magnetic fields
    • A variant of MRI called Functional MRI measures signal changes in the brain due to neural activity
    • MRI is used primarily for neurological (brain), musculoskeletal, cardiovascular and oncological (cancer) imaging
    • MRI is an anatomical imaging technology
    Nuclear medicine

    • Nuclear medicine uses radioactive isotopes and the principle of radioactive decay to study body functions
    • Nuclear medicine involves the administration into the patients of radio-pharmaceuticals.
      Radio-pharmaceuticals are substances with affinity for certain body tissues that have been labelled with radioactive tracers (called radio-nuclides)
    • The radio-pharmaceuticals administered into the body emit radiation which is detected and converted into images.
    • The radio-pharmaceuticals, once administered, localise (i.e. attach) to specific organs or cell receptors, meaning those particular organs or cells can be studied in isolation
    • Commonly used tracers include Technetium, iodine, gallium and thalium
    • Nuclear medicine is used mainly to study the heart, lungs, thyroid, liver and gallbladder
    • Nuclear medicine mainly provides information about the physiological function of these tissues
    • Since the radio isotopes decay over a period a time, they do not pose a significant threat to normal human functioning
    • Nuclear medicine is a functional imaging technology
    Positron Emission Tomography (PET)

    • PET uses nuclear medicines to produce three dimensional images
    • The PET system detects gamma rays emitted by positron emitting radio-nuclides. Images of the nuclide concentration are reconstructed in 3d by computer algorithms
    • PET is a functional imaging technology
    • PET is often combined with CT and MRI scans, enabling both anatomical and functional imaging simultaneously
    • PET was first developed by David Kuhl (USA) and Roy Edwards (USA) in the 1950s
    • PET is mainly used in oncology (cancer) and neurology (especially dementias)
    • A variant of PET, called Single Positron Emission Computed Tomography (SPECT) detects gamma rays emitted directly by the radio-nuclides

      PHYSICS: MAGNETISM

      Overview

    • The term magnetism describes how materials respond to an applied magnetic field
    • All materials are influenced to a greater or lesser extent by the presence of a magnetic field. Some are attracted (paramagnetism) while some are repulsed (diamagnetism)
    • Substances that are negligibly attracted by magnetic fields are called non-magnetic materials. Eg: copper, aluminium, water, glass
    • The magnetic state of a material depends on its temperature, with the result that a substance may exhibit different magnetic characteristics depending on its temperature
    • Magnetism can arise from either intrinsic magnetic moments contained in particles, or by electric currents applied to the substance
    • Magnet is a material that produces a magnetic field
    • Permanent magnet is a material that retain its magnetic field
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    Types of magnetism

    • Diamagnetism
      • Diamagnetism is the tendency of a material to oppose a magnetic field
      • It appears in all materials. However, in a material with paramagnetic properties, the paramagnetic behaviour dominates
      • Diamagnetic materials do not have unpaired electrons
      • Superconductors are diamagnetic materials
    • Paramagnetism
      • Paramagnetism is the tendency of a material to be attracted to an applied magnetic field
      • Paramagnetism only occurs in the presence of an externally applied magnetic field. When the external field is removed, the magnetisation will drop to zero
      • Paramagnetic materials have one unpaired electron, allowing it to orient in the direction of the magnetic field
      • Oxygen, myoglobin are examples of paramagnets
    • Ferromagnetism
      • Ferromagnetism is the only type of magnetism that can produce forces strong enough to be felt, and is responsible for the magnetic phenomena in everyday life
      • Ferromagnetic materials have unpaired electron, but unlike paramagnets, they remain oriented even after the external magnetic field has been removed
      • Ferromagnetic materials remain magnetized even after the external applied magnetic field has been removed
      • All permanent magnets are either ferromagnets or ferrimagnets
      • Eg: refrigerator magnets
    • Antiferromagnetism
      • Magnetic moments of electrons point in opposite directions
      • Anitferromagnets have zero net magnetic field
      • They are not very common and usually occur only low temperatures
      • Antiferromagnetism disappears above the Neel Temperature and the material becomes paramagnetic
      • Examples include hematite, chromium, iron manganese
    • Ferrimagnetism
      • Neighbouring pairs of electrons point in opposite direction
      • However, ferromagnetic materials retain their magnetisation in the absence of the magnetic field
      • Example is magnetite
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    Electromagnets

    • Electromagnet is a magnet whose magnetic field is produced by the flow of electric current
    • The magnetic field disappears when the current ceases
    • The electromagnet was invented by William Sturgeon (Britain) in 1824
    • Electromagnets are widely used in electrical devices such as motors, generators, loudspeakers, particle accelerators
    • Magnetic Levitation (MAGLEV) trains run on electromagnetic suspension produced by electromagnets
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    Earth’s magnetic field

    • The Earth’s magnetic field, which extends several tens of thousands of km into space is called the magnetosphere
    • The earth’s magnetic field is explained by dynamo theory. The theory explains the mechanism by which celestial bodies like the earth, or a star generate magnetic fields. According to the theory, earth’s magnetic field is produced by electric currents in the liquid outer core
    • The magnetic north pole of the Earth is located near the geographic south pole, and the magnetic south pole is located near the geographic north pole. This can be explained by understanding that the north pole of a suspended magnet points towards the north, indicating that the geographic north pole should have south polarity
    • The earth’s magnetic poles move with time due to magnetic changes in the earth’s core. Currently, the magnetic north pole lies near Ellesmore Island in northern Canada, while the south pole is near Wilkes Land, Antarctica. The north pole is moving northwest by about 64 km/year and the south pole is moving northwest by 10-15 km/year

      PHYSICS: ELECTRICITY

      Overview

    • Electricity is an extraordinarily versatile source of energy
    • Electricity is the backbone of modern industrial society
    • The phenomenon of electricity includes concepts such as
      • Electric charge: a property of subatomic particles that determines their electromagnetic interactions
      • Electric current: a movement or flow of charged particles
      • Electric field: influence of charged particles on other charged particles in the vicinity
      • Electric potential: capacity of an electric field to do work
      • Electromagnetism: interaction between electric and magnetic fields
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    TIMELINE OF EARLY DISCOVERIES/INVENTIONS


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    BASIC ELECTRICAL COMPONENTS
    1. Resistors
      1. Resistors are materials that resist the flow of current through them
      2. They dissipate energy in the form of heat
      3. Ohmic materials are those materials whose resistance remains constant over a range of temperatures and currents. Non-ohmic materials have resistances that change
      4. The unit of resistance is Ohm
    2. Capacitors
      1. Capacitors are devices that store electric energy in the form of electric charge
      2. They usually consist of two conducting plates separated by a thin insulating layer
      3. Capacitors block steady state current i.e. DC current
      4. The unit of capacitance is Farad
    3. Inductors
      1. Inductors are conductors that store energy in a magnetic field, which is produced in response to an electrical current
      2. Inductors allow steady current, but oppose rapidly changing currents
      3. The unit of inductance is Henry
    4. Transformers
      1. A transformer is a device that transfers electrical energy from one circuit into another
      2. This transfer occurs through inductively coupled conductors, where varying current in one circuit creates a varying magnetic field (and hence voltage) in the other circuit
      3. Transformers can be used to step-up or step-down voltages from high voltage transmission lines to appliances in homes
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    ELECTRICITY IN NATURE
    1. Electric shock
      1. A voltage applied to the human body causes an electric current through the tissues
      2. In general, greater the voltage applied, greater the current passed through the tissues
      3. Voltages 100-250 V can be lethal in humans, although as low 32V has been lethal sometimes. Lethality increases dramatically beyond 250V
      4. If the current is sufficiently high, it can cause muscle contractions, fibrillation of the heart and tissue burns
      5. DC tends to cause continuous muscle contractions making the victim hold on to a live conductor, thereby increasing risk of tissue burn
      6. AC tends to interfere with heart function, increasing risk of cardiac arrest
      7. AC at high frequencies, causes current to travel on the surface due to skin effect. This results in severe burn but is usually not fatal
    2. Electrical phenomena
      1. Touch, friction and chemical bonding are all due to interactions between electrical fields on the atomic scale
      2. The Earth’s magnetic arises from a natural dynamo of circulating currents in the planet’s core
      3. Piezoelectric crystals like quartz and sugar generate electric current when subject to mechanical pressure
      4. Electric eels detect and stun their prey via high voltages (500 V) generated from muscle cells called electrocytes
      5. Electrical currents, called Action Potential, are used for nervous system communication in all animals, including humans
    • Objects falling freely towards the earth’s surface have an acceleration due to gravity g = 9.8 \frac{m}{s^2} This is also known as g-force
    • Escape velocity is the speed needed to break free from a gravitational field. On the surface of the Earth it is 11.2 km/s
    • Weightlessness occurs in orbit when all gravitational forces acting on an object are uniformly distributed. Weightlessness does not occur due to an absence of gravity.
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