Optical wavelength

What is Optical Wavelength?

When there is a medium which has refractive index µ we have to use optical wavelength λ_µ.

The relation between optical wavelength and geometrical wavelength is given by 

λ_µ = λ / µ 

λ_µ = Optical wavelength

λ = Geometrical wavelength

µ = Refractive index of medium

Electromagnetic spectrum definition

The electromagnetic waves can be characterised by the parameters like wavelength, frequency, phase and state of polarization.

Wavelength :
The distance between two-crust or two throughs is known as wavelength. 
Wavelength denoted by λ.

Frequency : 
Frequency is the quantity that represents a number of oscillations that particle carries out in unit time.
Frequency denoted by ν.

Wavelength (λ) = c / Frequency (ν)

Where c = velocity of electromagnetic wave

Wavelength × Frequency = Velocity of the wave

The wavelength of the electromagnetic wave varies from 10^-12 meters to 10⁴ meters.

Phase :

The electromagnetic wave can be represented by a sine or cosine function.

E = E₀ Sin (wt + Φ )

Where E = Position of a wave at time t

E₀ = Maximum displacement of Amplitude

(wt + Φ ) = Phase of the wave

Φ = Initial phase or phase difference

Phase difference :

The difference between the phase if the two waves or phase of two position of a single wave is known as phase difference.

Wave optics Introduction

In a one-word optics can define that science of light.
Light has dual nature sometimes it behaves like a wave and sometimes it behaves like a particle.
In other word deal with optics is the branch of physics dealing with the study of optical phenomena.
The phenomena like reflection and refraction are explained by corpuscular theory. but the phenomena like interference, diffraction and polarisation can not explain the particle nature of light.
In optics, we consider the light as a wave.

We have also seen terms in optics are following below :

• Light 
• Electromagnetic Spectrum
• Wavelength
• Frequency
• Phase
• Phase difference
• Coherence
• Interference 

Coherence definition in physics

Coherence :

If the phase difference between two waves or phase difference between two positions of the single wave remains constant, such waves are known as coherent waves and phenomenon is called coherence.

If the phase difference between two sources changes then sources are known as incoherent. Sunlight, incandescent lamp. tube light etc is an example of the incoherent source.

There are two methods by which we can produce a coherent source :

• Division of wavefront
• Division of amplitude

Types of coherence :

• Temporal coherence
• Spatial coherence

Measurement of coherence :

The coherence of any source can be measured by the visibility of contrast of the fringe system produced by the source. It is given by 

V = I_max - I_min / I_max + I_min 

Where I_max = Maximum Intensity of bright fringe

I_min = Minimum Intensity of dark fringe

Ruby Definition

Ruby :

Ruby is synthetic aluminium oxide ( Al₂O₃ ) with 0.05 weight of chromium oxide ( Cr₂O₃ ) added to it.

It is the chromium that gives the ruby its characteristics red colour.

Full form of LASER

What is the full form of LASER?

Answer :

• Light Amplification of Stimulated Emission of Radiation

What does LASER mean?

The laser is a device that can amplify light and produce a highly directional, intense, monochromatic, and coherent beam.


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Application of laser

The main characteristics of laser radiation are following below.

• Coherence
• Very narrow bandwidth
• High directionality
• Extreme brightness

With the above characteristics, the lasers have a wide range of application in different disciplines such as physics, chemistry, medicine, engineering etc. 

Application of laser : 

• The laser is a coherent source, measurement of distances based on interferromagnetic techniques is made much simpler.
• The large distance can be also measured by laser. 
• The time taken for a laser pulse to travel from the laser to the target and back again is measured. Using such a method, the distance between earth and moon have been determined to an accuracy of +-0.15 m.
• The laser beam is highly intense hence it can be used in application like Laser beam welding, Laser cutting of material.
• The laser also is suitable for machining and drilling holes.
• The most successful therapeutic application of the laser has been in eye-surgery for the detached retina.
• Lasers also can serve as war-weapon for military purpose.
• The laser can be used for investigating the structure of molecules.
• Lasers also being employed for separating the various isotopes of an element.
• The narrowness of bandwidth of lasers, the strongest capacity for information in computers is improved.
• Due to a narrow bandwidth, lasers are used in microwave communication. so in the field of communications, laser offers unusual advantages.
• Lasers have also been used for the treatment of dental decay, the destruction of malignant tumours and the treatment of skin diseases.
• Genetic research using laser is quite popular.
• The IBM corporation is trying to transmit an entire memory bank from one computer to another by using a laser beam.

Disadvantages of manual process planning

Manual process planning (MPP) has many disadvantages. In this article, you can check it out some information on the disadvantages of manual process planning to know more about it.

Disadvantages of manual process planning :

• MPP is largely subjective.
• Incorporation of process changes is extremely difficult.
• The quality of the process plan is directly related to the experience and skill of the planner.
• It is difficult to check if the process plan is consistent and optimized.
• It is tiresome to search manually the process plans of similar parts form a large amount of documentation of the company.
• Technological changes of batch sized require the change in process plan.
• MPPs are slow to respond.

What is rigid body

What is Rigid body?

Answer :

A body is said to be rigid if, under the action of forces, it does not suffer any distortion.

Another way to said that the distance between any two points on the body remains constant.

Electron beam machining

Electron beam machining is processed by a high-velocity focused stream of electrons which heats, melts and vaporizes the work material at the point of bombardment thus metal will be removed. 

The production of free electrons is obtained from thermo-electronic cathodes wherein metal are heated to the temperature at which the electrons have sufficient speed for escape and make the space around the cathode. Thus the electrons accelerate and are carried by an electric field and by controlled magnetic fields are using for focusing and concentration of that electric field. The kinetic energy of a beam of free electrons is transformed into heat energy thus the interaction of the electrons with the workpiece material. Therefore EBM is also called thermo-electric process.

Operation principle of electron beam machining :

A beam of electrons is emitted from the electron gun which is basically a triode consisting of

• A cathode which is a hot tungsten filament ( 2500 degree C ) emitting high negative potential electrons.
• A grid cup, negatively based with respect to the filament.
• An anode which is heats at ground potential, and through which the high-velocity electrons pass.

A gun is supplied with electric current from a high voltage D.C source. The flow of electrons is controlled by the negative bias applied to the grid cup. The electrons passing through the anode are accelerated to two-third of the velocity of light by applying 50 to 150 kV at the anode and this speed id maintained till they strike the workpiece.
A magnetic deflection coil is used to make the electron beam circular and its a cross-sectional diameter is 0.01 to 0.02 mm and deflect it anywhere.
A microscope with a magnification of 40 on the workpiece enables the operator to accurately locate the beam impact and observe the machining operation.
As the beam impacts on the workpiece surface the kinetic energy of high-velocity electrons is converted into the thermal energy and it vaporized the material at the spot of its impact.

The application of the above process is also found in electron-beam drilling in which an organic or synthetic backing material is sandwiched on the other side of the component.

Accuracy :
Tolerance is about 10% of slot width or hole diameter.
Taper about 4 degrees included angle 
Depth to diameter ratio can reach 20:1 with multiple pulses.
Heat affected zone of up to 0.03 mm deep has been observed.

Application of EDM

The EDM provides economic advantages for making stamping tools, wire drawing and extrusion dies, header dies, intricate mould cavities.

It extremely used in aerospace industries, refractory metals, hard carbides and hardenable steels.

EDM application : 

• Drilling of micro-holes
• Thread cutting
• Helical profile milling
• Wire-cutting EDM
• Rotary forming
• Curved hole drilling
• Vacuum tubes

What is electric discharge machining

Electric discharge machining also is known as spark erosion.
It is the process of material removal based on the principle of metals by an interrupted electric spark discharge between the electrode tool and workpiece.

Working principle :

The main components of the EDM process are : 

• Electric power supply
• The dielectric medium 
• The workpiece and tool
• A servomotor

The basic process of EDM is really quite simple. The workpiece and the tool are electrically connected to D.C electric power supply. The workpiece is connected to the positive terminal of the electric source so that becomes the anode. The tool is a cathode. A gap is known as the 'spark-gap' in the range of 0.005 to 0.05 mm is maintained between the work piece and the tool.

In the spark gap produced spark is visible evidence of the flow of electricity. This electric spark produces intense heat with temperatures reaching 8000 to 12000 degree Celsius. The spark is controlled by very carefully and localized so that it affects the surface of the material only. 
The EDM process can be used in two different ways: 
1. A preshaped or formed electrode used as tool usually made from graphite is shaped to the form of the cavity it is to reproduce. The formed electrode is fed vertically down and the reverse shape of the electrode is eroded (burned) into the solid workpiece. 
2. A continuous-travelling vertical-wire electrode used as a tool and its diameter of a small needle or less is controlled by the computer. It follows a programmed path to erode the workpiece or cut a narrow slot to produce the required shape. 


The electrode ( Tools ) :

The shape of the tool will be basically the same as that of the product desired except that an allowance is made for side clearance and overcut.
The electrode materials generally used can be classified as metallic materials, non-metallic materials and a combination of metallic and non-metallic materials. Usually, copper, yellow brass, zinc and graphite are used for tools. Some low wearing tools are also used like silver-tungsten, copper-tungsten and metallized graphite. For commercial applications copper is best suited for fine machining. Aluminium is used for die-sinking while cast iron for rough machining.
One of the advantages of EDM is due to the fact that a tool made of a material softer than the workpiece material and which is a good conductor of electricity can be used to machine material of any hardness.
The wear of the tool in the EDM process due to electron bombardment is inevitable. 
The tool wears rates to determine the machining accuracy, tool movement, and tool consumption. 
The tool wear is the function of the rate of metal removal, the material of the workpiece, current setting, machining area, gap between the tool and workpiece and the polarity of the tool.

Wear ratio = Volume of work material removed / Volume of electrode consumed

Wear ratio = Depth of cut / Decrease in usable of the electrode

The wear ratio for carbon electrodes is up to 100:1.

For copper 2:1 

For brass 1:1

For copper tungsten 8:1

Purpose of Dielectric fluids :

• It used as a coolant for the workpiece and the tool. 
• It works as an insulating material during the charging of the condenser, as a result, perfect condition for efficacious spark discharge and its conduction when ionized is obtained. 
• The eroded materials are carried away by this medium. 
• It is a coolant in quenching the spark and prevents the arcing. 

Requirements of Dielectric fluids :

• Remain electrically nonconducting until the required break-down voltage has been reached.
• Breakdown electrically in the shortest possible time once the breakdown voltage has been reached.
• Have a good degree of fluidity.
• Be cheap and easily available.
• Be capable of carrying away the swarf particles.
• Inflammable. 
• It should be a hydrocarbon compound. 
• It should not produce toxic gases or vapours during the operation. 

Accuracy :

Tolerance value ( +- 0.05 ) mm could be easily achieved by EDM normal production.

By close control of the several variables tolerance ( +-0.003 ), mm could also be achieved.

Taper value id about to 0.005 to 0.05 mm per 100 mm depth.

An overcut of 5 to 100 micron is produced.

In no wear machining using graphite electrode a surface finish within 3.2 microns can be achieved.

Application of EDM :

The EDM provides economic advantages for making stamping tools, wire drawing and extrusion dies, header dies, intricate mould cavities.

It extremely used in aerospace industries, refractory metals, hard carbides and hardenable steels.

Some of its applications are following below :

• Drilling of micro-holes.
• Thread cutting.
• Helical profile milling.
• Wire-cutting EDM.
• Rotary forming.
• Curved hole drilling.
• Vacuum tubes.

Advantages and disadvantages of laser beam machining

Any solid material which can be melted without decomposition can be cut with the laser beam machining. To remove material from metallic or non-metallic surfaces, this process uses thermal energy. The high frequency of monochromatic light will fall on the surface and the material will be heated, melted and vaporized due to the impression of photons.
In this article, you can check it out some information on the advantages and disadvantages of laser beam machining to know more about it.

Advantages of laser beam machining : 

• No direct contact between tool and workpiece.
• No tool wear.
• Soft materials like rubber and plastics can be machined.
• Extremely small holes can also be machined.
• Machining of any material and also nonmetal is possible.
• Heat affected zone is small because of the collimated beam.
• Welding of dissimilar metal can also be performed efficiently.
• Any environment can be suitable for performing this process through transparent and magnetic fields.
• Drilling and cutting of areas not readily accessible are possible.

Disadvantages of laser beam machining : 

• One of the main disadvantages of that is it cannot be used to cut metals that have high heat conductivity or high reflectivity.
• Overall efficiency is extremely low.
• The process is limited to a thin sheet.
• Very low material removal rate.
• The machined hole is not round and straight.
• Cost is high.
• Output energy from LASER is difficult to control precisely.
• The laser system is quite troublesome since the life of the flash lamp is short.
• Too deep holes are not possible to drill.
• While machining some plastic bum or char is noticed.
• Experienced and skilled operators are required.
• Rate of production is low.

Application of laser beam machining

Laser beam machining applications :

• Suitable for exceptional cases like machining very small holes and cutting complex profiles in a thin and hard material like ceramics.
• Sheet metal trimming, blanking and resistor trimming.
• Used in mass micromachining production, not for mass material removal.
• Used in partial cutting or engraving.
• To drilling micro holes in turbine engine blades.
• In both soft and hard materials cutting.
• Scribing of any material.
• Patterning displays of all glass and plastic wafers and chips.
• Can be used for dynamic balance of rotating parts.
• Welding of non-conductive and refractory material.
• Jewellers also use laser welding on delicate pieces of jewellery.
• Laser beams perform intricate cuts in plastic.

Application of electron beam machining

Electron beam machining application : 

• To drill fine gas orifices.
• For use less than 0.002 mm work.
• In space nuclear reactors.
• Turbine blades for supersonic aero-engines.
• To produce metering holes in injector nozzles in diesel engines.
• To scribe thin films.
• To remove small broken taps from holes.
• In transmission assembly.
• To produce wire drawing die.

Advantages and disadvantages of electron beam machining

Electron beam machining is processed by a high-velocity focused stream of electrons which heats, melts and vaporizes the work material at the point of bombardment thus metal will be removed. Let us have a deep insight into the pros and cons of electron beam machining in this article. 

Advantages of electron beam machining :

• EBM is an excellent method for micro finishing.
• It can cut drill holes or cut slots which otherwise cannot be made.
• It is possible to cut any known material.
• No cutting tool pressure or wear occurred in this process.
• It is distortion free-machining so precise dimensions can be achieved.

Disadvantages of electron beam machining :

• High equipment cost.
• Highly skill operator required.
• Only small cuts are possible.

Advantages and disadvantages of EDM

Electric discharge machining also is known as spark erosion. It is the process of material removal based on the principle of metals by an interrupted electric spark discharge between the electrode tool and workpiece. Let us have a deep insight into the pros and cons that this process provided. 

Advantages of EDM : 

• It can be applied to all electrically conducting metals.
• Any complicated shape that can be machined.
• Machining time is less than conventional machining processes.
• It can also be employed for the extremely hardened workpiece.
• No mechanical stress is present in this process because of no contact between the tool and the workpiece.
• No burrs.
• Tolerances range +/- 0.005 can be achieved.
• Good surface finish can be attained.
• Creating small holes is not easily achieved by any other process other than EDM.
• Fragile and slender workplaces can be machined without distortion.
• The heat treatment process can be eliminated.
• Hard and corrosion-resistant surfaces, essentially needed for die making, can be developed by this process.
• Little or no polishing is required after the completion of the process.

Disadvantages of EDM : 

• Machining time is too long.
• Excessive tool wear.
• High specific power consumption.
• Profile machining of complex contours is not possible.
• Only able to machine conductive materials.
• The metal removal rate is slow.
• Reproduction of sharp corners is the limitation of the process.
• Surface cracking may take place in some materials owing to their affinity to become brittle at room temperature.
• Especially when higher energy per pulse is used.

Difference between kinematics and dynamics

Kinematics and dynamics are two branches of mechanics that deal with the motion of a particle that plays an important role in robotics and mechanical engineering field. 

What is kinematics?

A study that describes the motion of bodies and the system of bodies without taking into consideration of the cause of motion. 

What is the dynamics?

A study of the motion of a particle along with their cause like force and torque.

Now let us have a deep insight into the comparison between them and check some difference between kinematics and dynamics. 

Key difference : 

Kinematics will give you the values of change whereas dynamics provide the reasoning behind it. 

Kinematics :

• Kinematics originates from the Greek word kinesis, meaning motion.
• Galileo worked on with his numerous experiments measuring displacement, velocity and acceleration of balls rolling down inclined planes.
• More concern with the movement in general.
• A description of how objects move.
• kinematics describes movement, acceleration, speed, of objects.
• Kinematics is based on the nature of force, nature of the body.
• Kinematics is the geometry of motion.
• Motion is teated geometrically without reference to things like cause and effects. 

Dynamics :

• Dynamics from the Greek word dunamis which means power.
• Newton worked on when he formulated his three laws.
• Concern about measuring the causes and quantity of it and how it contributes and relates to the movement.
• It deals with force and why objects move as they do.
• Dynamics describes forces applied to the objects.
• Dynamics is based on the concept of force.
• Dynamics is geometry + physics of motion.
• Motion is treated in terms of trajectories and time so force and motion come in. 

What is Kinematics and Dynamics

What is Kinematics?

It deals with the relative motion of different parts of a mechanism without taking into consideration the forces producing the motions.

Kinematics is the geometry of motion.

What is Dynamics?

It involves the calculations of forces impressed upon different parts of the mechanism.

Dynamics is geometry + physics of motion.

The forces can be either static or dynamics.

Dynamics is further subdivided into two groups :

• Kinetics
• Statics

Kinetics is the study of forces when the body is in motion. 

Statics is the study of forces when the body is stationary.

Absolute entropy definition

Definition of Absolute Entropy :

Answer :

• The increase in entropy of a substance as it goes from a perfectly ordered crystalline form at 0 K temperature where its entropy considers as zero.