PHYSICS: NON-INVASIVE IMAGING
ü Medical imaging is the technique and process used to create images of the human body for medical purposes
ü Non-invasive imaging is the method of producing images of internal tissues without surgical procedures
ü 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)
ü As a discipline, it includes radiology, nuclear medicine, endoscopy, thermography etc
ü Non-invasive imaging is a vast field with differing technologies such as X-rays, tomography, MRI etc
ü Non-invasive imaging provide highly valuable diagnostic tools for diagnosing and treating varied ailments such as cancer, fractures, etc
ü Imaging technologies can be broadly classified into two categories
Ø Anatomical imaging modalities: these imaging techniques provide information on the anatomy i.e. the physical structure of the organ/tissue under study
Ø Functional imaging modalities: these imaging techniques provide information on the physiological functioning of the organ/tissue under study
X-RAYS
ü X-rays were discovered by Wilhem Conrad Rontgen (Germany) in 1895. He won the Nobel in Physics 1901
ü Radiography is the imaging process that uses X-rays to capture images
ü In conventional radiography, X-rays from a X-ray tube pass through the patient and are captured by an X-ray sensitive film screen
ü 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
ü X-rays are the preferred diagnostic tool for studying lungs, heart and skeleton (including fractures) due to their simplicity, available and low cost
ü X-rays is an anatomical imaging technology
Fluoroscopy
ü Fluoroscopy is used to obtain real time moving images of the internal structures
ü 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
ü Fluoroscopes use low x-ray radiation doses
ü Fluoroscopy also involves use of radiocontrast agents that increase the contrast of a specific tissue w.r.t. surrounding tissuesby strongly absorbing or scattering the x-rays
ü The radiocontrast agents enable visualization of dynamic processes such as peristalsis in the digestive tract of blood flow in arteries and veins
ü Commonly used contrast agents include Barium and Iodine. These may be administered orally or rectally or injected into the blood stream
ü Used mainly for investigating gastrointestinal functions, orthopaedic surgery and urological surgery
ü Fluoroscopy is a functional imaging technology
Computed Tomography (CT)
ü Computed Tomography uses X-rays in conjunction with software algorithms to image the body
ü CT generates a three-dimensional image of an object using a large series of X-ray images taken around a single axis of rotation
ü CT produces a volume data which can be manipulated in order to demonstrate various body functions
ü Compared to traditional radiography, CT produces 3d information and has much higher contrast and resolution, but also uses much higher doses of radiation
ü CT scanners were first developed by Sir Godfrey Hounsfield (Britain) in 1972. He won Nobel in Medicine in 1979
ü CT is used primarily for detecting cerebral haemorrhage, pulmonary embolism, aortic dissection, appendicitis and kidney stones
ü CT is an anatomical imaging technology
Ultrasound
ü Ultrasound was first developed for medical use by John Wild (Britain) in 1949
ü Ultrasonography uses ultrasound (high frequency sound waves) to visualize soft tissues in the body in real time
ü Ultrasound does not involve any ionizing radiation, hence it considered safer than X-rays or CT and is used for obstetrical imaging
ü Ultrasound is limited by its inability to image through air or bone, and by the skill of the examiner
ü Ultrasound is used primarily to study the development of foetus
ü A variant of ultrasound, the colour flow Doppler ultrasound is used in cardiology for diagnosing peripheral vascular disease
ü Ultrasound is a functional imaging technology
Magnetic Resonance Imaging (MRI)
ü MRI was invented by Paul Lauterbur (USA) and Sir Peter Mansfield (Britain) in the 1970s. They won Nobel in Medicine in 2003
ü 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
ü The working principle of MRI is called Nuclear Magnetic Resonance (NMR)
ü MRI scans give the best soft tissue contrast of all imaging modalities
ü MRI does not use any ionizing radiation. However, it does use powerful magnetic fields
ü A variant of MRI called Functional MRI measures signal changes in the brain due to neural activity
ü MRI is used primarily for neurological (brain), musculoskeletal, cardiovascular and oncological (cancer) imaging
ü MRI is an anatomical imaging technology
Nuclear medicine
ü Nuclear medicine uses radioactive isotopes and the principle of radioactive decay to study body functions
ü 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)
Radio-pharmaceuticals are substances with affinity for certain body tissues that have been labelled with radioactive tracers (called radio-nuclides)
ü The radio-pharmaceuticals administered into the body emit radiation which is detected and converted into images.
ü 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
ü Commonly used tracers include Technetium, iodine, gallium and thalium
ü Nuclear medicine is used mainly to study the heart, lungs, thyroid, liver and gallbladder
ü Nuclear medicine mainly provides information about the physiological function of these tissues
ü Since the radio isotopes decay over a period a time, they do not pose a significant threat to normal human functioning
ü Nuclear medicine is a functional imaging technology
Positron Emission Tomography (PET)
ü PET uses nuclear medicines to produce three dimensional images
ü The PET system detects gamma rays emitted by positron emitting radio-nuclides. Images of the nuclide concentration are reconstructed in 3d by computer algorithms
ü PET is a functional imaging technology
ü PET is often combined with CT and MRI scans, enabling both anatomical and functional imaging simultaneously
ü PET was first developed by David Kuhl (USA) and Roy Edwards (USA) in the 1950s
ü PET is mainly used in oncology (cancer) and neurology (especially dementias)
ü A variant of PET, called Single Positron Emission Computed Tomography (SPECT) detects gamma rays emitted directly by the radio-nuclides
PHYSICS: MAGNETISM
ü The term magnetism describes how materials respond to an applied magnetic field
ü 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)
ü Substances that are negligibly attracted by magnetic fields are called non-magnetic materials. Eg: copper, aluminium, water, glass
ü 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
ü Magnetism can arise from either intrinsic magnetic moments contained in particles, or by electric currents applied to the substance
ü Magnet is a material that produces a magnetic field
ü Permanent magnet is a material that retain its magnetic field
Types of magnetism
ü Diamagnetism
Ø Diamagnetism is the tendency of a material to oppose a magnetic field
Ø It appears in all materials. However, in a material with paramagnetic properties, the paramagnetic behaviour dominates
Ø Diamagnetic materials do not have unpaired electrons
Ø Superconductors are diamagnetic materials
ü Paramagnetism
Ø Paramagnetism is the tendency of a material to be attracted to an applied magnetic field
Ø Paramagnetism only occurs in the presence of an externally applied magnetic field. When the external field is removed, the magnetisation will drop to zero
Ø Paramagnetic materials have one unpaired electron, allowing it to orient in the direction of the magnetic field
Ø Oxygen, myoglobin are examples of paramagnets
ü Ferromagnetism
Ø 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
Ø Ferromagnetic materials have unpaired electron, but unlike paramagnets, they remain oriented even after the external magnetic field has been removed
Ø Ferromagnetic materials remain magnetized even after the external applied magnetic field has been removed
Ø All permanent magnets are either ferromagnets or ferrimagnets
Ø Eg: refrigerator magnets
ü Antiferromagnetism
Ø Magnetic moments of electrons point in opposite directions
Ø Anitferromagnets have zero net magnetic field
Ø They are not very common and usually occur only low temperatures
Ø Antiferromagnetism disappears above the Neel Temperature and the material becomes paramagnetic
Ø Examples include hematite, chromium, iron manganese
ü Ferrimagnetism
Ø Neighbouring pairs of electrons point in opposite direction
Ø However, ferromagnetic materials retain their magnetisation in the absence of the magnetic field
Ø Example is magnetite
Electromagnets
ü Electromagnet is a magnet whose magnetic field is produced by the flow of electric current
ü The magnetic field disappears when the current ceases
ü The electromagnet was invented by William Sturgeon (Britain) in 1824
ü Electromagnets are widely used in electrical devices such as motors, generators, loudspeakers, particle accelerators
ü Magnetic Levitation (MAGLEV) trains run on electromagnetic suspension produced by electromagnets
Earth’s magnetic field
ü The Earth’s magnetic field, which extends several tens of thousands of km into space is called the magnetosphere
ü 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
ü 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
ü 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
ü Electricity is an extraordinarily versatile source of energy
ü Electricity is the backbone of modern industrial society
ü The phenomenon of electricity includes concepts such as
Ø Electric charge: a property of subatomic particles that determines their electromagnetic interactions
Ø Electric current: a movement or flow of charged particles
Ø Electric field: influence of charged particles on other charged particles in the vicinity
Ø Electric potential: capacity of an electric field to do work
Ø Electromagnetism: interaction between electric and magnetic fields
TIMELINE OF EARLY DISCOVERIES/INVENTIONS
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
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
PHYSICS: PARTICLE PHYSICS
ü The atom was discovered by John Dalton in 1802
ü However, even more fundamental particles were discovered in the 20th century
ü Particle physics focuses on subatomic particles including electrons, protons and neutrons
ü Many fundamental particles do not occur in nature but can be created in high energy collisions of other particles
Standard Model of particle physics
ü The Standard Model describes the current classification of elementary particles
ü It describes strong, weak and electromagnetic forces using gauge bosons
ü The Standard Model does not include gravitation, dark matter and dark energy
ü The Standard Model was developed by Sheldon Glashow, Steven Weinberg and Abdus Salam in the 1960s. They won Nobel in Physics in 1979
ü The Model contains 24 fundamental particles
ü It predicts the existence of the Higgs Boson, which is yet to discovered
ü All particles of the Standard Model have been observed in experiments, except the Higgs Boson
Elementary particles
ü All elementary particles are either fermions or bosons
ü Fermions are particles associated with matter, while bosons are particles associated with force
ü Fermions can be divided into Quarks and Leptons
ü Bosons can be divided into Gauge Bosons and Other Bosons (including Higgs Boson)
ü Protons and neutrons are examples of Hadrons, which are composites of Quarks
ü Electrons are elementary particles by themselves
Important particle physics labs
| Facility | Location | Established | Famous for |
| Brookhaven National Lab | New York | 1947 | World’s first heavy ion collider World’s only polarized proton collider |
| Budker Institute of Nuclear Physics | Novosibirsk (Russia) | 1959 | World’s first particle accelerator |
| European Organization for Nuclear Research | Geneva | 1954 | World’s largest particle physics lab Birthplace of World Wide Web Large Hadron Collider (LHC) |
| German Electron Synchrotron (DESY) | Hamburg | 1959 | |
| Fermilab | Chicago | 1967 | Tevatron – world’s second largest particle accelerator |
| High Energy Accelerator Research Organization (KEK) | Tsukuba (Japan) | ||
| SLAC National Accelerator Lab | Stanford University | 1962 | Longest linear accelerator in the world |
PHYSICS: NUCLEAR PHYSICS
Nuclear Fission
ü Nuclear fission is a reaction in which the nucleus of an atom splits into smaller parts
ü Nuclear fission can either release energy or absorb energy: for nuclei lighter than iron fission absorbs energy, while for nuclei heavier than iron it releases energy
ü Energy released can be in the form of electromagnetic radiation or kinetic energy
ü The amount of free energy contained in nuclear fuel is about a million times that contained in a similar mass of chemical fuel (like petrol)
ü The atom bomb or fission bomb is based on nuclear fission
ü Example: fission of Uranium-235 to give Barium, Krypton and neutrons
Nuclear Fusion
ü Nuclear fusion is the process by which multiple nuclei join together to form a heavier nucleus
ü Nuclear fusion can result in either the release or absorption of energy: for nuclei lighter than iron fusion releases energy, while for nuclei heavier than iron it absorbs energy
ü Nuclear fusion is the source of energy of stars.
ü Nuclear fusion is responsible for the production of all but the lightest elements in the universe. This process is called nucleosynthesis
ü Controlled nuclear fusion can result in a thermonuclear explosion – the concept behind the hydrogen bomb
ü The energy density of nuclear fusion is much greater than that of nuclear fission
ü Only direct conversion of mass into energy (collision of matter and anti matter) is more energetic than nuclear fusion
ü Example: fusion of hydrogen nuclei to form helium
PIONEERS OF NUCLEAR PHYSICS RESEARCH
| Scientist | Nationality | Discovery | Recognition |
| J J Thomson | Britain | Electron (1897) | Nobel in Physics (1906) |
| Henri Becquerel | Belgium | Radioactivity (1896) | Nobel in Physics (1903) |
| Ernest Rutherford | New Zealand | Structure of atom (1907) | Nobel in Chemistry (1908) Regarded as the father of nuclear physics |
| Franco Rasetti | Italy/USA | Nuclear spin (1929) | |
| James Chadwick | Britain | Neutron (1932) | Nobel in Physics (1935) |
| Enrico Fermi | Italy/USA | Nuclear chain reaction (1942) Neutron irradiation | Nobel in Physics (1938) |
| Hideki Yukawa | Japan | Strong nuclear force (1935) | Nobel in Physics (1949) |
| Hans Bethe | Germany/USA | Nuclear fusion (1939) | Nobel in Physics (1967) |
APPLICATIONS OF NUCLEAR PHYSICS
| Application | Developed by | Working principle | Use |
| Nuclear power | Enrico Fermi (Italy, 1934) | Nuclear fission | Power generation |
| Nuclear weapons | Enrico Fermi (Italy, 1934) Edward Teller (USA, 1952) | Nuclear fission Nuclear fusion | Weapons |
| Radioactive pharmaceuticals | Sam Seidlin (USA, 1946) | Radioactive decay | Cancer, endocrine tumours, bone treatment |
| Medical imaging | David Kuhl, Roy Edwards (USA, 1950s) | Nuclear magnetic resonance (for MRI) Positron emission (for PET) | MRI: Musculosketal, cardiovascular, brain, cancer imaging PET: cancer, brain diseases imaging |
| Radiocarbon dating | Willard Libby (USA, 1949) | Radioactive decay of carbon-14 | Archaeology |
IMPORTANT NUCLEAR RESEARCH FACILITIES
Nuclear research facilities in the world
| Facility | Location | Established | Famous for |
| Brookhaven National Lab | New York | 1947 | Until 2008 world’s largest heavy-ion collider |
| European Organization for Nuclear Research (CERN) | Geneva | 1954 | World’s largest particle physics lab Birthplace of the World Wide Web Large Hadron Collider (LHC) |
| Fermilab | Chicago | 1967 | Tevatron – world’s second largest particle accelerator |
| ISIS | Oxfordshire (England) | 1985 | Neutron research |
| Joint Institute for Nuclear Research | Dubna, Russia | 1956 | Collaboration of 18 nations including former Soviet states, China, Cuba |
| Lawrence Berkeley National Lab | California | 1931 | Discovery of multiple elements including astatine, and plutonium |
| Lawrence Livermore National Lab | California | 1952 | |
| Los Alamos National Lab | New Mexico, USA | 1943 | The Manhattan Project |
| National Superconducting Cyclotron lab | Michigan | 1963 | Rare isotope research |
| Oak Ridge National Lab | Tennessee | 1943 | World’s fastest supercomputer – Jaguar |
| Sudbury Neutrino Lab | Ontario | 1999 | Located 2 km underground Studies solar neutrinos |
| TRIUMF (Tri University Meson Facility) | Vancouver | 1974 | World’s largest cyclotron |
| Yongbyon Nuclear Scientific Research Centre | Yongbyon, North Korea | 1980 | North Korea’s main nuclear facility |
| Sandia National Lab | New Mexico, USA | 1948 | Z Machine (largest X-ray generator in the world) |
| Institute of Nuclear Medicine, Oncology and Radiotherapy (INOR) | Abbottabad, NWFP (Pakistan) | ||
| Pakistan Institute of Nuclear Science and Technology (PINSTECH) | Islamabad | 1965 |
Nuclear research facilities in India
| Facility | Location | Established | Famous for |
| Bhabha Atomic Research Centre | Bombay | 1954 | India’s primary nuclear research centre India’s first reactor Apsara |
| Variable Energy Cyclotron Centre (VECC) | Calcutta | 1977 | First cyclotron in India |
| Institute for Plasma Research (IPR) | Gandhinagar | 1982 | Plasma physics |
| Indira Gandhi Centre for Atomic Research (IGCAR) | Kalpakkam | 1971 | Fast breeder test reactor (FBTR) KAMINI (Kalapakkam Mini) light water reactor Built the reactor for Advanced Technology Vessel (ATV) |
| Saha Institute for Nuclear Physics | Calcutta | 1949 | |
| Tata Institute for Fundamental Research (TIFR) | Bombay | 1945 |
PHYSICS: OPTICS IN EVERYDAY LIFE
Working of the Human Eye
ü Light entering the eye passes through the cornea and the pupil
ü Then, the lens focuses light onto an array of photoreceptor cells in the back of the eye, called the retina
ü There are two types of photoreceptor cells:
Ø Rod cells: they are responsible for black and white vision, night vision and peripheral vision. They are more in number
Ø Cone cells: they are responsible for colour vision. They are less numerous in number
Defects in vision
ü Presbyopia: as people age, the lens becomes less flexible and near point recedes from the eye. As a result objects far away cannot be see. Can be corrected using a converging lens
ü Hyperopia: lens cannot decrease focal length to focus on nearby objects and so nearby objects cannot be see. Corrected using a converging lens
ü Myopia: lens cannotincrease focal length to focus on far away objects and so farther objects cannot be seen. Corrected using a diverging lens
ü Astigmatism: occurs when the cornea is not spherical but instead elongated. Results in distorted images. Corrected using a cylindrical surface lens
Applications of Mirrors
ü Kaleidoscope: A toy in which multiple images are formed by two mirrors placed inside a tube
ü Periscope: Two plane mirrors fixed facing each other 45 degrees. Used in submarines
ü Concave mirror: When used close to face gives magnified image. Used for shaving, personal care etc
ü Convex mirror: Produces smaller image but gives wider range of view. Used in rear view mirrors
ü Parabolic mirror: A concave mirror whose section is the shape of a parabola, helps in focusing. Used as reflectors in search lights, car head lights etc
Optical instruments and their applications
| Instrument | Working principle | Applications |
| Microscope | Convex lens (converging lens) system consisting of very short focal length eyepiece and longer focal length objective | Magnifying tiny objects: molecular studies |
| Telescope | Convex lens system that provides regular magnification | Magnifying distant objects: astronomy |
| Binocular | Pair of telescopes mounted side-by-side | General use |
| Interferometer | Superposition of waves | To study interference properties of light |
| Photometer | Uses a light sensitive element (like photomultiplier) to measure light intensity | Used to measure reflection, scattering, fluorescence etc |
| Polarimeter | Light from a source passing through a polarizer and then measured | Measures dispersion or rotation of polarized light |
| Spectrometer | Works by measuring light intensity | Used to measure light properties: astronomy |
| Autocollimator | Projects and image onto a target mirror and measures deflection of returned image | Component alignment, measure deflection in optomechanical systems |
Optics in the atmosphere
| Observed effect | Underlying cause | Description |
| Blue colour of sky | Rayleigh scattering | Higher frequencies (blue light) get more scattered than lower frequencies |
| Red colour of sunrise and sunset | Mei scattering | Scattering due to suspended particles (like dust) when sun’s rays have to travel longer distance |
| Halos/afterglows | Scattering | Scattering off ice particles |
| Sundog | Scattering | Scattering off ice crystals causing bright spots on the sky |
| Mirage | Refraction | |
| Novaya Zemlya effect | Refraction | Sun appears to rise earlier than predicted |
| Fata Morgana | Refraction due to temperature inversion | Objects beyond the horizon can be seen elevated |
| Rainbow | Total internal reflection |
Optics for photography
| Desired effect | Approach |
| Close up | Use macro lens |
| Long shot | Telephoto lens |
| Panoramic pictures | Wide angle lens |
| Handle low light conditions | Increase exposure time (decrease shutter speed) |
| Fast moving objects | Decrease exposure speed (increase shutter speed) |
| Increase depth of field (foreground and background both in focus) | Increase aperture i.e. f-number |
Optical Fibres
ü Optical fibres are glass or plastic fibre that carries light
ü Advantages include
Ø low signal loss
Ø immunity from electromagnetic interference
Ø higher bandwidth (data rate)
Ø low power consumption
ü Optical fibres work on the principle of Total Internal Reflection
ü Applications include long distance communication, endoscopy, light decorations etc
PHYSICS: WAVES
ü A wave is a disturbance that travels across space and time
ü Propagation of waves usually involves transference of energy without transferring mass. This is achieved by oscillations or vibrations around fixed locations
ü Mechanical waves require a medium for transmission (e.g. sound)
ü Electromagnetic waves do not require a medium and can travel in vacuum (e.g. light)
ü Longitudinal waves are those with vibrations parallel to the direction of wave propagation. E.g. sound waves
ü Transverse waves are those with vibrations perpendicular to the direction of travel. E.g. electromagnetic waves including light
ü Waves on a string are an example of transverse waves
Properties of waves
1. Reflection: It is the change in direction of a wave at the interface between two media. Examples include reflection of light, sound etc
2. Refraction: It is the change in direction of a wave due to a change in its speed. Examples: refraction of light when it passes through a lens
3. Diffraction: Bending of waves as they interact with obstacles in their path. Example: rainbow pattern when light falls on a CD or DVD
4. Interference: Superposition of two waves that come into contact
5. Dispersion: the splitting up of waves by frequency
6. Polarization: the oscillation of a wave in only one direction. Exhibited only by transverse waves (like light), not exhibited by longitudinal waves (like sound)
Wave properties in everyday life
ü The floor of a lake or the ocean appears closer than it actually is. This is because of refraction of light
ü The red ring around the Sun is due to diffraction of light
ü We can hear but not see across corners, this is because of diffraction of sound (e.g. we can hear but not see a person in the next room)
ü The rainbow and the blue colour of sky are both due to dispersion of light
ü Sunglasses use polarization filters to block glare
SOUND WAVES
About Sound
ü Sound is a mechanical wave that is transmitted as longitudinal waves through gases, plasma and liquids. However, in solids it can travel as both longitudinal and transverse waves
ü Sound cannot travel in vacuum, it needs a medium for propagation
ü The speed of sound in air is 330 m/s
Perception of sound
ü The frequency range 20 Hz to 20 MHz is known as the audible range, where human beings can detect sound waves
ü The upper frequency limit decreases with age i.e. as we get older, our ability to detect higher pitches (shrills) decreases
ü Other species uses different ranges for hearing. E.g. dogs can perceive frequencies higher than 20 KHz
ü Increased levels of sound intensity can cause hearing damage. Hearing can be damaged by sustained exposure to 85 dB or by short term exposure to 120 dB sound. A rocket launch usually involves about 165 dB
Sonar systems
ü Sound Navigation and Ranging is a technology that uses sound propagation for navigation and communication
ü Primarily used under water because light attenuates very quickly in water whereas sound travels farther
ü First developed by R.W. Boyle and A.B. Wood in 1917 in Britain
ü Applications include military, fisheries, wave measurement, ocean-floor mapping etc
ü Sonar is used by marine mammals (like dolphins and whales) for communication as well
ü Bats communicate by means of SONAR at frequencies over 100 MHz (beyond the human range)
ELECTROMAGNETIC WAVES
Electromagnetic Spectrum
Electromagnetic radiation and applications
| Radiation | Applications |
| Radio waves | RADAR, TV, cell phones, microwaves |
| Microwaves | Wi-Fi |
| Infrared (IR) | Night vision, thermography, imaging |
| Visible light | Sight |
| Ultraviolet (UV) | Sun burn, water disinfection |
| X-rays | Astronomy, medicine |
| Gamma rays | PET scans, cancer therapy, astronomy, food sterilization |
Radar systems
ü Radio Detection and Ranging is a technology that uses radio waves to identify moving and fixed objects
ü Developed by Robert Watson-Watt in 1935 in Britain
ü Radar works by measuring the waves that are reflected back from an object. Radar can detect objects at ranges where sound or visible light would be too weak
ü Applications include aircraft detection, air traffic control, highway speed detection, weather detection etc
More about electromagnetic waves
ü Radio waves are reflected by the ionosphere and hence can be received anywhere on the earth.
ü TV transmission penetrates the ionosphere and hence is not received like radio waves. Thus TV transmission is limited to line-of-sight
ü At night, the radio reception improves because the ionosphere is not exposed to sunlight and hence is more settled
ü Bats communicate by means of SONAR at frequencies over 100 MHz (beyond the human range). Other animals like dolphins and whales use SONAR as well
PHYSICS: HEAT
ü Heat is the process of energy transfer from one system to another
ü Units of heat: Joules (J), Calories, British Thermal Unit (BTU)
ü Temperature is a measure of internal energy (enthalpy)
ü Heat transfer can happen spontaneously only from a warmer to a colder body. Reverse heat transfer can only happen with the aid of an external source such as a heat pump.
Mechanisms of heat transfer
ü Conduction is the most significant heat transfer mechanism in solids. It occurs as hot high energy molecules interact with neighbouring and transfer heat to them. Eg: heat transfer from one end of a metal rod to another
ü Convection is most significant in liquids and gases. This happens when hot molecules move and transfer energy to other molecules. Eg: boiling of water. When water is heated on a stove, hot water from the bottom rises and displaces colder liquid which falls.
ü Radiation is the only form of heat transfer possible in the absence of a medium. Heat is transferred in the form of electromagnetic radiation. Eg: heat from the sun reaching the earth.
Heat transfer in everyday life
ü Copper is used in construction of boilers and cooking utensils because it is a good conductor of heat
ü Air is a poor conductor
ü Wool and cotton are good insulators i.e. poor conductors. Their insulation arises mainly due to air spaces between molecules
ü Double-walled glass doors with air between them are better insulators than windows with a single thick glass layers
ü Eskimos live in snow huts because snow is a poor conductor of heat, and hence protects them from the extreme cold outside.
ü Land and sea breeze, ocean currents are arise due to convection
ü The boiling point of water at sea level and atmospheric pressure is 100C. When extra heat is added, it changes the phase of water from liquid to gas (water vapour).
Thermometers
ü Thermometers can be divided into two groups:
Ø Primary thermometers: measure temperature directly based on the property of matter. They are relatively complex and not used commonly. Eg: thermometers based on velocity of sound in gas, thermal noise of an electrical resistor etc.
Ø Secondary thermometers: measure temperature relative to a pre-calibrated quantity. They are easy to use and used commonly.Alcohol thermometer, mercury thermometer, medical thermometer are all secondary thermometers
ü In cold winter places, alcohol thermometers are used instead of mercury thermometers because the freezing point of alcohol is lower
ü For extra-low temperature measurements (-200 C), Pentane is used
ü Water is not suitable for use in thermometers because it freezes at 0 C and has irregular expansion
ü Mercury is used for common medical thermometers because
Ø It does not cling to glass and hence reading is easy
Ø It is opaque and easily seen
Ø Its expansion is uniform and hence calibration is easier
Ø It is a better conductor of heat than alcohol and hence responds more rapidly to changes of temperature
Ø It has low specific heat capacity and hence is more sensitive
Common appliances based on heat
ü Solar cooker: is a box made of insulating material such as wood, cardboard etc. The box has a glass cover to retain heat inside by greenhouse effect. The inside of the box is painted black to increase heat absorption.
ü Pressure cooker: Pressure cooker increases the boiling point of water by increasing pressure. When the boiling point of water increases, food cooks faster. Pressure cookers are especially essential in hill stations because at higher altitudes the boiling point of water decreases due to lower atmospheric pressure
ü Refrigerator and Air-conditioner: are heat pumps that transfer heat from inside to the external environment. They use a refrigerantwhich is a compound that undergoes reversible phase change from gas to liquid. Common refrigerants include ammonia, sulphur dioxide, carbon dioxide and methane. The use of chlorofluorocarbons has been phased out due to concerns regarding depletion of the ozone layer.