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Friday, 30 October 2020

Improving Energy Efficiency and Air Circulation Using BIM Technology

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Building Information Technology (BIM) has been a revelation in the field of construction. It has helped us improve the construction field by making a digital representation of the building details. It gives an idea and 3D view about the functional and physical properties of each and every part of the building. Even a door or a window can studied to the minutest of details and improve the efficiency. It helps the Engineers and contractors to visualise the proceedings prior to the actual work and help reduce the waste and improve the efficiency level of the building. The project puts forward an idea to reduce the energy consumption for the building and also improve the air circulation. Energy reduction is of great importance in the current world and the proposed idea is of great significance. The air circulation can improve the mental and physical conditions of the occupants and hence have a good impact on the living conditions.


The BIM technology helps create a 3D view of the building which helps for a better understanding of the space in building, materials used and the system as a whole. The softwares commonly used to develop a BIM model are Autodesk Revit, Autodesk BIM360, ArchiCad, Sketch Up. In the project a sustainable model of building is developed and compute the energy consumption of the building. In the BIM technology we can design a building considering the properties of lighting, shadows and natural sun light. While designing we can maximize the use of the natural sunlight and thereby reduce the artificial lighting requirements. Large amounts of energy is consumed for human comforts. We can improve natural air circulation and thereby improve the thermal conditions inside the building. A continuous movement of air will ensure better living conditions and reduce the need of artificial fan and AC. Smart building and design can also  utilize the solar energy available.

Figure: BIM Cycle

The energy analysis can be done making use of BIM authoring tools. The energy analysis report is obtained using Insight 360. The energy utilization of building is analyzed by Energy Use Intensity (EUI) in Kilowatt per year, and improvements are done accordingly.

For studying the ventilation, the 3D image of building developed is integrated with computational fluid dynamic (CFD) modelling within a BIM platform. It can improve the positioning of doors and windows of building, and hence improve the thermal conditioning inside the building. The 3D model is converted to CFD model to analyse the air circulation.

Improving Energy Efficiency and Air Circulation Using BIM Technology

For analysing the energy demand of building, first we create a conceptual level climatic study of the building. Then create an architectural and structural model of the project. For that make use of BIM authoring tools. The properties of materials used in each and every part of building can be given as an input to the tool. So all physical and parametric properties of the material is recorded in the tool. This will give an idea about the properties of materials like heat transfer coefficient, energy embodied value etc. After the analysis a report is made on the energy use by Insight 360 tool. The rest is analysed and Energy Use Intensity is calculated.

EUI.   = {Total Energy Consumption for building/ Total floor area}

The analysis report will also have many options like optimising operation schedule, building operations, lighting efficiency and others, to alter the energy consumption levels. The tools like Auto desk Insight can be used. It is a cloud based energy analysis tool, that can help in improving the energy and environmental performances of building and consider the solar and lighting approaches for the building.

The energy efficient model developed in such a manner can also have an improvement in the natural air ventilation facilities. The 3 dimensional BIM model can be transferred to SAT format for conversion of external air into a 3 dimensional format. Later it is sent back to BIM software and transferred into the CFD simulation software. The geometry of the work is simplified for analysis process. The most required places are considered and others are neglected. For inlet, the boundary conditions like air velocity air temperature are defined. All the specified parameters are specified and visualised in the CFD format. Turbulence flow and heat transfer models are developed in CFD. The CFD simulations are integrated with BIM platform, and it will give a better understanding of air movement. While returning to BIM model, make the required adjustments in physical model to improve the airflow by comparing with CFD model ippo. The final 3 D model is developed in the BIM platform.

Discussions and Conclusions

BIM is an ever growing technology and it can be used in various situations to bring further improvements in the construction technologies. Information about the weather conditions needs to considered while designing for a better natural ventilation. Average wind speed, humidity and temperature are given as an input to the designing tools. Energy and material wastage can also be reduced to a great extent using BIM technology. So by creating an energy efficient building the cost of building has been proved. With a further improvement of the ventilation properties of the building,   the living conditions inside the building has also been increased. So the proposed projects fetches both health and economic benefits. Computer aided Engineering has improved recently with the different tools available. Now we can study the wind loads on buildings, pedestrian comforts in urban areas, control and analyse the air quality, predict the spread of smoke and many. The benefits of the technology have a never ending list and we can strive to improve the living conditions and efficiency of our built in environment.

Saturday, 17 October 2020

Power Electronics Lab Viva Questions

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Power Electronics Lab Viva Questions and Answers

1. What you understand about the Safe Operating Area (SOA) of a power device?

The boundaries of voltage and current in which the power device can be operated without destructive failures can be determined by the SOA. The SOA of a bipolar power transistor is given below:

2. What are cycloconverters? List the different types of cycloconverters?

The main use of a cycloconverter is to convert a constant frequency, constant voltage AC signal to another frequency AC waveform. By synthesizing the output waveforms from the AC supply segments, this can be achieved.

There are mainly two types of cycloconverters

(a) Step down cycloconverter

By using forced communication, a step down cycloconverter gives the output with frequency lower than the input frequency.

(b) Step up cycloconverter

By using line communication, a step up cycloconverter gives an output with frequency greater than the input frequency.

3. What you know about the operational amplifiers (Op Amps)?

Basically op-amp is a integrated circuit (IC), which can be used to work as a voltage amplifier. An op-amp has two inputs with different polarity hence it is fed with a differential input. So op-amp has two different polarity inputs and single output. An op-amp circuit gets high gain i.e., the output signal is very high as compared to input signal. There are mainly two types of op-amps.

(a) Inverting op-amps:

A inverting amplifier possesses negative feedback. The input is given to the inverting terminal (-ve terminal) of the op-amp and the non-inverting terminal is grounded. R1 is the input resistance and R2 is the feedback resistance.

(b) Non-inverting amplifier

The non-inverting amplifier gives amplified output signal and the output is in phase with the input signal.

4. Write the equations for gains of inverting and non inverting amplifiers?

Gain of non inverting op-amp is

Gain of inverting amplifier is

5. What you understand about forced communication?

By the effect of external circuitry, the current flowing through the thyristor is forced to become zero. This process is termed as forced communication.


6. List down the different types of voltage controlled (voltage driven) devices?

The different types of voltage controlled devices are:



7. In AC mode, what does the voltmeter shows?

In AC mode, the multimeter shows  the Root Mean Square (RMS) value of voltage or current. In DC mode, the multimeter shows only the RMS value.


8. What you understand about the  holding current of a SCR?

The minimum mandatory current for holding the SCR in forward conduction state is known as the holding current. The SCR switches from the state of forward conduction to forward blocking state, if the forward current is less than the holding current.

9. What you understand about universal motors?

Universal motors can be used for working with single phase AC source as well as DC source. It is often known as single phase series motor and is a commutation type motor. The motor runs in the same direction, when we reverse the polarity of the line terminals of a DC series motor. We cannot run a DC series motor as a universal motor, even though both are built in similar manner. Universal motors are widely used for speed control and high speed application purposes.  They can be used in wash machines, power drills, kitchen applications and blowers.


10. What you know about the hard switching of a thyristor?

The SCR can be said to be hard fired, if the gate current is very-very higher than the required gate current. This will enhances the di/dt capability and reduces the turn ON time.


11. MOSFET or IGBT is used for high voltage applications?

IGBT is mostly preferred for high voltage applications. For breakdown voltage up to 1000 V, IGBT is commonly used.

Fig : IGBT

MOSFET are commonly used for breakdown voltage less than 250V. 


12. What is the process of commutation?

The direction of current flow is changed in a particular path of the circuit for turn off the SCR. This process is called commutation.


13. Discuss about the control strategies of chopper?

The different control strategies of chopper are:

Frequency Modulation (constant TON or TOFF , variable frequency)

Current Limit Control (CLC)

Pulse Width Modulation PWM (Variable TON, constant frequency)


14. What you understand about the latching current of SCR?

The minimum current required to turn on (latch) the SCR from forward blocking state to forward conduction state is termed as the latching current.

15. For isolating the power circuits, power semiconductor from the low-power circuits which components are used?

Transformers and Opto-Couplers


16. What you know about natural commutation?

The process of enabling the thyristor to turn off and the current flowing through the thyristor goes through a natural zero is called natural commutation. Natural commutation occurs in AC circuits.

17. For DC applications, is it possible for using fuses with an AC voltage rating?

Fuses can be rated for using voltage AC or DC.  Normally the DC voltage rating of fuses is half of the maximum AC voltage rating.


18. For Turn ON the SCR, what methods you know?

For turn on the SCR, different voltage triggering methods are used. They are:

 (a) Light Triggering

 (b) Gate Triggering

 (c) dv/dt Triggering

 (d) Temperature Triggering


19. List the different types of current driven (current controlled) devices?

The different types of current controlled devices are:





20. Discuss about the characteristics of an ideal op amp?

The different characteristics of an ideal op amp are:

(a) Infinite input impedance Rin, and so zero input current

(b) Infinite open-loop gain G = Vout / Vin

(c) Infinite bandwidth with zero phase shift and infinite slew rate

(d) Zero output impedance Rout

(e) Zero input offset voltage

(f) Infinite power supply rejection ratio.

(g) Zero noise

(h) Infinite common-mode rejection ratio (CMRR)

(i) Infinite output voltage range.


21. Relating to the commutation process, what are the different types of commutations you know?

(a) Voltage commutated chopper

(b) Load commutated chopper

(c) Current commutated chopper


22. Give some examples of power electronics applications?

(a) Speed control of motors

(b) Uninterruptible Power Supply (UPS)

(c) Switch Mode Power Supply (SMPS)

(d) ICU


23. What you know about a snubber circuit?

The snubber circuit is a series combination of a resistor and a capacitor in parallel with the SCR. The circuit is mainly used for the dv/dt protection of SCR.


24. IGBT or MOSFET is most commonly used for high frequency applications? Justify your answer?

Since MOSFET has low switching losses than IGBT, MOSFET is commonly used for high frequency applications. For the applications of frequency range upto 20 KHz, IGBT are used and for frequency range greater than 200 KHz, MOSFET are used.


25. What you know about the duty cycle of a chopper?

The duty cycle of a chopper can be defined as the ratio of ON time of the chopper to the total time period of the chopper.

26. List the advantages of freewheeling diode in rectifier circuits?

The advantages of freewheeling diodes are:

(a) Input power factor is improved

(b) The load current waveform is improved

(c) Prevents the output voltage from becoming negative


27. What you know about the firing angle (delay angle) of an SCR?

The firing angle also known as delay angle can be defined as the angle between the zero crossing of the input voltage and the instant the SCR is fired. When the zero crossing of supply voltage takes place, one pair of thyristor is forward biased. These SCRs are triggered after the delay angle (α).

28. What are the uses of special machines?

The limitations of general purpose motors (Induction motors, synchronous motors) are they are neither precision position nor precision speed motors. For the applications of high precise position and high precise speed, special purpose motors (Stepper motors, PMDC motors etc) are commonly used.


29. What you know about a Permanent Magnetic DC motor (PMDC)?

A PMDC is same as that of an ordinary dc shunt motor. In PMDC, the field is provided by permanent magnets structure instead of salient- pole wound field structure.

The major advantages of PMDC are:

(a) Low noise

(b) Small size

(c) Low manufacturing cost

(d) High efficiency

There are mainly three types of permanent magnets used.

(i) Rare-Earth magnets

(ii) Ceramic magnets

(iii) Alnico magnets

Thursday, 8 October 2020

Network Analysis Viva Questions and Answers

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1.  What you understand about the Q-factor of a coil?

We can define the Q factor of a coil as the ratio of inductive reactance to the resistance of a coil. Q factor refers to the ohmic losses of a coil with dimensionless unit and is inversely proportional to the coil quality.

Q factor = (inductive reactance )/(resistance of a coil). 

2. Write down the examples of different types of current sources?

The devices which can be treated as current sources are the semiconductor devices like transistors and diodes.

3. How much efficiency can be attained during the maximum power transfer situation?

Will get  maximum of 50% efficiency.

4. How can you define a filter?

Basically a filter is an electrical circuit, that is used for transmit signals with a specified frequency range.

5. What you know about an active filter?

Active filters involves components like operational amplifiers (OP-AMP). This op-amp circuit will introduce some gain in the signal. In other words, we can say that active filters is the type of filter which are designed using active components.  The amplifiers included in filter design yields for the improvement of predictability, cost and performance of a filter.

6. How will you construct a band pass filter?

We can construct the band pass filter as a combination of two parallel tuned circuits and is a special type of LC circuit. The purpose of band pass filter is to allow a particular bandwidth frequency. 

7. What you know about resistance of a material?

The resistance of a material is the property of a material for opposing the current flowing through the material. In other words, we can say that the property of opposing current through any material gives the resistance of that material. It is usually measured in ohms (Ω)

8. When current becomes zero (0), what happens to voltage?

When current reaches zero, voltage becomes constant.

9. For high voltage and frequency, which capacitor is usually used?

For high voltage and frequency applications, the ceramic capacitors are most commonly used. 

We can easily control the thickness of the ceramic dielectric layer and can be produced as per the requirement of the desired voltage. The maximum rated voltage level of ceramic capacitors is 30 KV.

10. Explain Kirchoff 's voltage law and what are its limitations ?

As per Kirchoff 's voltage law, the algebraic sum of all branch voltages around any closed loop is zero in a network for all time instances. 

The main limitation of Kirchoff 's voltage law is that in a distributed parameter network, the law is not applicable

11. Discuss Norton's Theorem?

Any linear bilateral network with output terminals can be changed by a single current source in parallel with Z (a single impedance).

12. What you understand about the maximum power transfer theorem?

 In a dc network, when the load resistance and internal resistances becomes equal, the maximum power is transferred from source to the load. The maximum amount of power transferred is 50%.

13. What is the characteristic impedance of a network?

The characteristic impedance, also termed as the surge impedance can be calculated by the ratio of the amplitudes of voltage and current of a single wave propagates along the line. It is denoted by Z0.

14. Discuss Kirchoff 's current law?

Kirchoff 's current law states that at any node of a network, the algebraic sum of currents through the node is always equal to zero. In other words at a particular node, the sum of incoming currents and outgoing currents are same. 

15. Give the advantages of constant K filters?

The main advantages of constant K filters are:

(a) In constant K filters, beyond the cut-off frequencies the attenuation doesn't rapidly increases.

(b) In the pass band, the characteristic impedance widely varies from the desired value.

16. For the formation of a resistor, what type of materials are used?

The materials used for the formation of a resistor are:

(a) Constantan (it is an alloy of nickel and copper. Nickel 45% and Copper 55%).

(b) Manganin (it is an alloy of copper, manganese and nickel. Nickel 2%, Manganese 12%,   and Copper 86%).

17. In what situation, the three terminals of a resistor is used?

When the resistance is less than 1 ohm, the three terminals are used. 

18. How we can calculate the equivalent impedance in Thevenin's theorem?

 In  Thevenin's theorem, the equivalent resistance can be calculated by, short circuiting all independent voltage sources and open circuiting all the independent current sources present in the circuit.

19. What is an unilateral circuit?

In an unilateral circuit, for both directions, the properties are not same. In other words we can say that unilateral circuits allows current to flow only in one direction. 

20. List down the practical applications of filters?

The main applications of filters are they can be used in

(a) Voice frequency telegraphy

(b) TV broadcasting and telegraphy

(c) Multichannel communication

(d) Power supplies

(e) Audio electronics

(f) Radio communications

21. What you know about inductance?

The property of a electric conductor for opposing any change in the electric current passes through it can be termed as inductance. In a conductor, the flow of current creates a magnetic field around it.

Inductance of a coil:


L is the inductance in Henries (H), 

VL is the voltage across the coil (V) and

di/dt is the rate of change of current in Amperes per second (A/s).

22. List the properties of a resistor?

The main properties of resistors are:

(a) Resistance to oxidation

(b) Corrosion and moisture

(c) High resistivity

(d) Mechanical strength

(e) Resistance value tolerance

(f) Protection against influences from the environment.

(g) Low temperature coefficient of resistance

(h) Low noise properties.


23. Differentiate active and passive networks?

The passive network has no current or voltage sources, while the active network has either current or voltage source.

24. What are the characteristics of a filter?

Under the pass band frequencies, an ideal filter will transmit signals without attenuation and completely suppresses the stop band frequencies. In other words, we can say that an ideal filter has  a sharp cut-off profile.

25. What is the cut-off frequency. Draw the cut-off frequency for LPF?

The cut-off frequency can be defined as the frequency that separates the pass band and the attenuation band.

26. When current through an inductor remains constant, what happens to the voltage?

When current flowing through an inductor is constant, the voltage across the inductor     becomes zero (0). 

27. For making inductance coil, which material is used?

Marble is used for making the inductance coil because it will not get affected by atmospheric conditions.

28. Whether the theorems are applicable for ac sources?

No. They are applicable for dc circuits only.

29. Explain Ohm's law?

Ohm's law states that by keeping the physical condition as unchanged, the current through any conductor is directly proportional to the applied potential difference across it.

I = V/R

Where, I is the current, V is the voltage and R is the resistance.

30. What are the examples of voltage source and explain what are dependent sources?

The examples of voltage sources are battery and generator. 

If strength of voltage or current changes in the source for any change in the connected network, then the network can be termed as dependent sources. 

31. What is the units of current, charge and attenuation?

Current - Ampere (A)

Charge - Coulombs (C)

Attenuation - Decibel (dB) and Neper (Np)

32. How capacitance can be defined?

The capacitance can be defined as the ability to store electric charge within it. It is actually a measure of charge per unit voltage that can be stored in an element.

33. How can you define the Norton equivalent circuit?

The current generator placed in parallel to the internal resistance gives the Norton equivalent circuit.

34. List the advantages of active filters?

The main advantages of active filters over passive filters are:

(a) It is easy to tune

(b) It gives gain

(c) It eliminates bulky components

(d) It can be used for low impedance loads.

35. Define branch in a circuit?

Branch can be defined as a part of network that lies between two junction points.

36. Explain Thevenin's theorem?

Thevenin's theorem states that any linear network with output terminal can be changed by a single voltage source V in series with a single impedance. 

37. State and explain Superposition Theorem? 

In any linear bilateral resistive network having two or more voltage sources the current through any branch is the algebraic sum of the currents produced by each source acting alone at a time, when all other sources are replaced by their internal resistances.

Friday, 2 October 2020

Investigatory Project in Physics Format

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Experimentation in practical classes of Class 11 and Class 12 forms an integral part of Physics Education. The present system of Physics Education of high school and higher secondary section of CBSE and state level is based on memory-based, content-oriented and teacher-centred methods. Though this system gives hands-on-experience, it neither gives insight into the deep intricacies of the problem nor does it help in identifying the basic working principles and apparatus used.

The rapid developments as well as the recent shift in trends of Science Education demand an approach which is problem-based, performance-based, activity-oriented and above all learner-centred. Investigatory projects are included in the curriculum to cater to this need. The performance of an investigatory project helps in the development of the art of creative thinking and reasoning, distinguishing facts from fallacies and reaching a conclusion based on actual observations and their analysis. It makes a student curious and confident to take up any problem, however complex it appears. A careful and skillful observation of sequences during an activity enhances personal investigation capabilities. Group activity helps in developing skills of sharing a complex job and the experience of working in a group, over and above the normal objectives of investigatory projects.

An investigatory project is an in-depth study of a problem connected with a topic in the curriculum. It can be fully open-ended, a comprehensive study of a known technique or problem or can be survey of an idea, a technique or procedure. The project differs from the routine practical in the sense that known facts, contents, relations and fixed procedures are not taken for granted. Instead, the students develop their own ingenious experimental procedures, carry out analysis in their own way and present the result in a manner, which they think most appropriate. Often, students come up with fresh, fascinating and novel ideas and explanations. They reach the final conclusion based on their own rational thinking and the knowledge they acquired.

The involvement of the student is of prime importance in the culmination of an investigatory project. Before carrying out any activity, the guide should be consulted and his/her concurrence obtained. This guideline should he followed strictly, as many a scientific procedure involve the risk of danger and accident, often unknown to students. The teacher-guide should not interfere with the project unnecessarily. It does not mean that the teacher-guide should keep completely aloof. The guide should be watchful and ready to interfere at any moment, in case of necessity.

It is essential that the students should maintain clear, detailed chronological notes of what they are doing and what they are trying to achieve. The guide should periodically review these notes.

An investigatory project in Physics can consist of the following steps.


(i) Identification of the Problem


An investigation always starts with questions. Questions may arise from something that is learnt in class or from observations in the laboratory or surroundings. Such questions are discussed, singled out and sharpened enough so that it can be taken up as a project.


(ii) Collection of Related Information


Though the question may appear to be fresh to students, the answer may be avail-able in textbooks. If not, related information would be available in familiar books or elsewhere. Enough information should be collected from books and other sources. The resources of the INTERNET can also be made use of. Competent persons out-side the institution can also be consulted. It is also essential to know whether others are working on same or similar problems. The collected information should be well documented.


(iii) Establishment of a Law or Hypothesis


Based on the information collected and documented, a working hypothesis may be formed. It is an attempt to find an answer or explanation to the problem. The hypothe-sis can be tested using analytical/numerical methods or by experimentation. It is often possible to make predictions based on the hypothesis.


(iv) Experimentation


After forming the hypothesis, an experiment or a theoretical procedure is to be de-signed to test it. This involves assessing the requirements, choosing the necessary apparatus, forming a methodology for performing the experiment and designing, the details of the observations to be taken. The experiment requires extensive stepwise planning and execution. Everything should be documented sequentially in detail so that the experiment can be performed with ease. The necessary apparatus are to be collected and studied. It is imperative that a complete procedure of the experiment and a carefully designed format of observations should be prepared well in advance. The experiment should then be performed under different conditions and observations recorded. The methodology is altogether different form the usual way of doing Physics practical. The arrangement of the apparatus, the process of making observations etc., should be done with utmost care. Unexpected odd observations and other curious behaviour should not be taken lightly and discarded under any circumstances, but carefully noted for later analysis. Such observations may end up in some new idea, hypothesis or explanation.


(v) Conclusion and discussion


The data that has accumulated during the experiment is now carefully analysed. Necessary calculations are made to get the required results. Graphs, charts and other similar methods can be used for display of data and conclusions. Computers can also be made use of. The results are compared with the predictions of the hypothesis. In the event of any discrepancies, an attempt is made to explain the observed phenomena.

The discussion of the result forms the core of the investigatory project. The data and conclusions are interpreted to the fullest possibility. The opinions of experts in the field can be sought, if necessary. Limitations of the experiment, possibility of probable errors, scope for further improvement, etc., should also be included.


vi) Presentation of the Project Report


Finally the project should be fully documented, ready for presentation in the form of a project report or a dissertation or a research paper. The dissertation format is advisable at the plus two stage. The report may be organised in the following manner.

• The report should bear a title, which reflects the nature of the project. It should be novel and eye catching. Usually, during the course of the project work a suitable title evolves naturally.

• A certificate of genuineness from the teacher-guide should be included next. The certificate should bear the title of the project, the details of the student, including the register number of the examination.

• There should be an introduction, indicating the actual problem and its back-ground. The methodology of tackling the problem and a very brief conclusion of the project should also be given. Acknowledgement for help sought from the guide and others can be given, if not included separately.

• The main body of the project report comes next. It can be divided into chapters, if long enough. Alternatively, the body can be organised into paragraphs numbered serially as 1.1, 1.2, 1.2, ... , 2.1, 2.2, 2.3,… , 3.1, 3.2, 3.3, .... The main paragraphs may be arranged as follows.


(a) Detailed discussion of the problem, indicating it as sharply as possible and the strategy for solving it.

(b) Details of experimentation, indicating the apparatus and their specifications, materials required and the mode acquisition, layout, diagrams, theoretical considerations, and other relevant facts.

(c) Detailed step by step procedure for the actual performance of the experiment and specific, clear details of taking observations.

(d) Details of precautions to be taken, indicating chances of mishap/accident and probable errors likely to affect the observations.

(e) Detailed tabular forms of observations, mentioning the title, measuring instruments, units etc.

(f) Details of repetition of the experiment, mentioning the changes in experimental conditions and variables.

(g) Discussion of results showing formulae, calculations, graphs and charts, computer printouts, etc.

(h) A conclusion giving the exact problem, strategy for tackling it and the result of the investigation, personalised views, limitations of the present setup, scope for future improvement etc.

(i) List of references forming a bibliography.

The report should either be hand written neatly or typed and presented in a file or in bound form. It should then be got certified by the teacher-guide and preserved carefully for presentation at the examination.