Polarisation of light

Light is a form of energy. It has many properties. In some cases, light behaves like a flux of particles, and in some cases like waves. Thatswhy wave-particle dual nature assigned to light. Rectilinear propagation of light, reflection and refraction hints at particle nature whereas interference, diffraction etc. leads to wave nature. If we assume wave nature, there can be two types-longitudinal and transverse. Polarization phenomenon of light establish transverse nature of light. Polarized light can be produced by reflection, refraction (pile of plates), scattering, selection absorption and double refraction. Calcite and quarts are doubly refracting materials. Both refracted rays seems to be polarized. Nicol prism, a device fabricated from calcite crystal is used as polarizer and analyzer. Half wave plates and quarter wave plates are effectively used to produce plane polarized light, elliptically polarized light and circularly polarized light. some materials rotate the plane of polarization of light. They are called optically active materials. Quartz, sugar crystals, tartaric acid, sugar solution are examples. Polarimeter is a device used to determine the angle(amount) of polarization.

Interference of Light

Interference of Light

The superposition of two or more light waves and redistribution of their energies is called interference.

Coherent waves

Sources used should be coherent to observe interference phenomenon. Coherent waves are light waves with same frequency, which maintain the same phase or constant phase difference over a distance and time.

Superposition of two coherent waves-Constructive and Destructive Interference.

When two waves are in phase, the amplitude of the resultant wave is equal to the sum of amplitudes of the two waves. The interference produced at these points is known as constructive interference leading to bright band.

When two waves are in opposite phase, amplitude of the resultant wave is equal to zero. The interference produced at these points is known as destructive interference leading to dark band.

If the path difference between two waves is equal to nλ, it results in constructive interference.

If the path difference between two waves is equal to (2n+1) λ/2, it results in destructive interference.

The regions of brightness and darkness are also known as regions of maxima and minima.

Shock Waves

Any fluid that propagates at supersonic speeds (Supersonic waves are mechanical waves which travel with speeds greater than that of sound), give rise to shock waves. Shock waves are produced in nature during earth quakes and when lightning strikes. Shock waves can be produced by a sudden dissipation of mechanical energy in a medium enclosed in a small space.

Applications of shock waves

1. Cell information

2. Wood preservation

3. In pencil industry

4. Kidney stone treatment

5. Gas dynamic studies

6. Shock wave assisted needleless drug delivery

7. Treatment of dry borewells

8. For compaction of ceramic powders

9. In the design of engines, jets, rockets and turbines

10. In the design of ducts and pipes

11. In the treatment of bone fractures

Methods of creating shock waves in the laboratory using a shock tube

1.Using a Reddy shock tube

2. Detonation

3. Very high pressure gas cylinder

4. Combustion

5. Using small charge of explosives

Four-stroke cycle petrol engine

Four-stroke cycle operation in automobile engines is common nowadays. The four strokes in the operation of a four-stroke cycle petrol engine are suction stroke, compression stroke, power stroke and exhaust stoke. The inlet valve should keep open and exhaust valve closed during suction stroke. Downward movement of piston creates a partial vacuum inside the cylinder. This leads to sucking of the mixture of air and petrol into the cylinder. Both the inlet and exhaust valves are closed during the compression stroke. The compressed mixture gets vapourized and a spark is produced in the spark plug igniting the mixture during this stroke. Inlet and exhaust valves remain closed during power stroke. But the burning of gas forces exhaust valve to open. During the exhaust stroke, the inlet valve is closed and the exhaust valve is open. Here the burnt gas is pushed out of the cylinder which forces exhaust valve to close and inlet valve open.

Water logging

Water logging is the situation when the productivity of agricultural land gets affected by the high waterablity. Water logging results in ill-aeration of plants. Water logging also makes tilling and ploughing processes difficult. Water logging also leads to the growth of unwanted plants like grass, weeds etc. and affects the growth of the crops. Water logging is responsible for bacterial activity retardation. Water logging also leads to salinity of soils. A saline soil reduces osmotic activity of the plants. Thus crop yield is very much affected by water logging. Some important causes for water logging are intensive irrigation, seepage of water from the adjoining high lands, inadequate surface drainage, inadequate natural drainage, impervious obstruction, seepage of water through canals, irregular topography, submergence due to the floods and excessive rains. The important measures employed for water logging control are introduction of lift irrigation, reducing the intensity of irrigation, provision of intercepting drains, introduction of crop rotation, lining of canals, provision of an efficient drainage system, improving the natural drainage and optimum use of water.

Plastic deformation mechanisms in metals

The permanent changes in shape and dimensions of metals can be carried out by plastic deformation mechanisms. Crystal structure and lattice parameters remain unaltered during plastic deformation. Plastic deformation increases the number of imperfections in metals. The two main processes involved in plastic deformation are slip and twinning. In slip, atoms move over a number of interatomic distances relative to their initial positions. The displacement step magnitude is equal to full interatomic distance. The orientation of displaced region and undeformed region remains the same. Movement by an atom is a fraction of interatomic distance in twinning process. The orientation of twinned region and untwined regions are not same. Slip mechanism is preferred during high temperature and lower strain rate cases. At lower temperature, high strain rate cases, twinning is employed.

Nanobuds

Nanotechnology has already become an important field in the medical field for diagnostic and drug delivery applications. Carbon-60 molecules which are also known as fullerene promises good appliance in medical field. Cylindrical fullerenes are known as carbon nanotubes. Carbon nanotubes can be synthesized in many forms. Single walled nanotubes and multi walled nanotubes are two important materials. A carbon nanotubes bent into a torus is known as nanotorus. Carbon nanobuds are latest member in Nanomaterials category which is created by the combination of carbon nanotubes and fullerenes. Fullerene in the form of buds is connected to carbon nanotubes by covalent bonding in nanobuds. Bonding is achieved between fullerene buds and sidewalls of carbon nanotubes. The main application of nanobuds is in field emission applications since they are excellent field emitters. Since the fullerene buds prevents slipping of nanotubes, nanobuds can be used as molecular anchors.

Spool valves

Control valves are required in pneumatic and hydraulic systems to direct and regulate the flow of fluid from compressor or pump to the various load devices. Relief valves are infinite position valves. Finite position valves are used for passage or blocking of fluid flow. There can be either two or four parts for control valves. The three major types of control valves are poppet valves, rotary valves and spool valves. Simple discs, balls and cones are used in poppet valves. The two varieties of poppet valves are 2/2 simple valve and 3/2 valve. Poppet valves are economical but require large operating force. Rotary valves are used for hand operation in pneumatic systems. They are compact and have low operating forces. Spool valves are constructed with a spool moving horizontally within the valve body. The spool can be easily moved as there is no net force acting on the spool due to system pressure. There are two types of spool valves. They are two-way spool valve and four-way spool valve. Spools are shifted during the operation of spool valves. For this, a button, lever or a solenoid is used.

Microwave tunnel diodes

Tunnel diodes can be used in microwave applications. Quantum tunneling theory is used to explain the tunneling phenomenon that take place in tunnel diodes.  Tunneling phenomenon is actually a majority carrier effect. Some of the advantages of tunnel diodes are low cost, less weight, high speed, low noise, high peak current to valley current ratio and low power operations. These parameters make tunnel diodes ideal candidate in applications like microwave amplification and microwave oscillation. The tunnel diode is a p-n junction semiconductor diode with negative resistance. Tunnel effect is responsible for this negative resistance. Heavy doping is employed during the construction of tunnel diodes. In tunnel diodes, Fermi level lie inside the valence band in p-region and inside the conduction band in n-region. While using for amplifier applications, tunnel diodes are connected either in parallel or in series with a resistive load. Another common practice is connecting tunnel diode to a microwave circulator.

Leaf springs

A spring is the component of a vehicle which serves the purpose of absorbing the shock developed while it is in motion. There are two varieties here. They are tension spring and compression spring. In a tension spring load is connected to one end leading to tension (extension). In a compression spring, the loading results in compression. Leaf springs are specially designed springs which are mounted on vehicles for suspension purposes.  A number of leaf springs bound by a nut and bolt arrangement is widely preferred in vehicles. Commonly used configuration is semi elliptical. On the application of load, friction is developed between the leaf plates. A casing around the leaf plate prevents the accumulation of dust and grit materials. To reduce friction, a lubricant, preferably grease with graphite is applied between the plates. To facilitate bending and springing, one plate is allowed to slide against another.