HOW TO PREPARE FOR PHYSICS VIVA VOCE

Generally, questions start from the experiment you did, but further
questions depend on your answers.

To perform well in viva you should have a thorough knowledge about the
apparatus and procedure as well as the associated theoryv

Visit http://physics.2lv.in for sample viva questions

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The Diamond Ring Solar Eclipse

Solar eclipse 

Eye Safety During Solar Eclipses

Visit the Nasa Site (http://eclipse.gsfc.nasa.gov) for more details

The Sun can be viewed safely with the naked eye only during the few brief seconds or minutes of a total solar eclipse. Partial eclipses, annular eclipses, and the partial phases of total eclipses are never safe to watch without taking special precautions. Even when 99% of the Sun's surface is obscured during the partial phases of a total eclipse, the remaining photospheric crescent is intensely bright and cannot be viewed safely without eye protection [Chou, 1981; Marsh, 1982]. Do not attempt to observe the partial or annular phases of any eclipse with the naked eye. Failure to use appropriate filtration may result in permanent eye damage or blindness!

Generally, the same equipment, techniques and precautions used to observe the Sun outside of eclipse are required for annular eclipses and the partial phases of total eclipses [Reynolds & Sweetsir, 1995; Pasachoff & Covington, 1993; Pasachoff & Menzel, 1992; Sherrod, 1981]. The safest and most inexpensive of these methods is by projection, in which a pinhole or small opening is used to cast the image of the Sun on a screen placed a half-meter or more beyond the opening. Projected images of the Sun may even be seen on the ground in the small openings created by interlacing fingers, or in the dappled sunlight beneath a leafy tree. Binoculars can also be used to project a magnified image of the Sun on a white card, but you must avoid the temptation of using these instruments for direct viewing.

The Sun can be viewed directly only when using filters specifically designed for this purpose. Such filters usually have a thin layer of aluminum, chromium or silver deposited on their surfaces that attenuates ultraviolet, visible, and infrared energy. One of the most widely available filters for safe solar viewing is a number 14 welder's glass, available through welding supply outlets. More recently, aluminized mylar has become a popular, inexpensive alternative. Mylar can easily be cut with scissors and adapted to any kind of box or viewing device. A number of sources for solar filters are listed below. No filter is safe to use with any optical device (i.e. - telescope, binoculars, etc.) unless it has been specifically designed for that purpose. Experienced amateur and professional astronomers may also use one or two layers of completely exposed and fully developed black-and-white film, provided the film contains a silver emulsion. Since all developed color films lack silver, they are always unsafe for use in solar viewing.

Unsafe filters include color film, some non-silver black and white film, medical x-ray films with images on them, smoked glass, photographic neutral density filters and polarizing filters. Solar filters designed to thread into eyepieces which are often sold with inexpensive telescopes are also dangerous. They should not be used for viewing the Sun at any time since they often crack from overheating. Do not experiment with other filters unless you are certain that they are safe. Damage to the eyes comes predominantly from invisible infrared wavelengths. The fact that the Sun appears dark in a filter or that you feel no discomfort does not guarantee that your eyes are safe. Avoid all unnecessary risks. Your local planetarium or amateur astronomy club is a good source for additional information.

In spite of these precautions, the total phase of an eclipse can and should be viewed without any filters whatsoever. The naked eye view of totality is completely safe and is overwhelmingly awe-inspiring!


Watching Solar Eclipse Safely

1999 Diamond Ring Effect 

The Pinhole Projection Method

One safe way of enjoying the Sun during a partial eclipse--or anytime--is a "pinhole camera," which allows you to view a projected image of the Sun. There are fancy pinhole cameras you can make out of cardboard boxes, but a perfectly adequate (and portable) version can be made out of two thin but stiff pieces of white cardboard. Punch a small clean pinhole in one piece of cardboard and let the sunlight fall through that hole onto the second piece of cardboard, which serves as a screen, held below it. An inverted image of the Sun is formed. To make the image larger, move the screen farther from the pinhole. To make the image brighter, move the screen closer to the pinhole. Do not make the pinhole wide or you will only have a shaft of sunlight rather than an image of the crescent Sun. Remember, this instrument is used with your back to the Sun. The sunlight passes over your shoulder, through the pinhole, and forms an image on the cardboard screen beneath it. Do not look through the pinhole at the Sun.


SCIENCE AND RELIGION

JOSELIN

          A scientist’s religious feeling takes the form of a rapturous amazement at the harmony of natural law which reveals an intelligence of such superiority that compared with it, all the systematic thinking and acting of human beings is an utterly insignificant reflection. This feeling is the guiding principle of his life and work, in so far as he succeeds in keeping himself from the shackles of selfish desire. The knowledge of truth as such is wonderful, but it is so little capable of acting as a guide that it cannot prove even the justification and the value of the aspiration toward that very knowledge of truth.

         Science is the century old endeavor to bring together by means of systematic thought the perceptible phenomena of this world into as thorough going an association as possible. It is the attempt at the posterior reconstruction of existence by the process of conceptualization.

        A religiously enlightened person has liberated himself from the fetters of his selfish desires and clings to thoughts and aspirations of super personal value.

Religion is the age old endeavor of mankind to become clearly and completely conscious of the values and goals and to constantly strengthen and extend their effect. If

One conceives of religion and science according to these definitions then a conflict between them appears impossible. For science can only ascertain what is, but not what should be. Religion on the other hand deals only with evaluations of human thought and action; it cannot justifiably speak of facts and relationships between facts.

       A conflict arises when a religious community insists

On the absolute truthfulness of all statements recorded in the Bible. This means an intervention of the part of religion into the sphere of science. Nevertheless, there exist between the realms of religion and science strong reciprocal relationships and dependencies.

      Science can only be created by those who are thoroughly imbued with the aspiration toward truth and understanding. This source of feeling, however, springs from the sphere of religion.

“Science without religion is lame,

Religion without science is blind.”

                        -Albert Einstein

101 APPLICATIONS OF BERNOULLI’S THEOREM - PROJECT

 This is an open project for students (especially to students of Kendriya Vidyalaya, Pattom Shift 1) to find out an post 101 Applications of Bernoulli's Theorem.
Instructions
  • Post your ideas as comments. Your comments will be copied to the article if acceptable.
  • Try to find out more applications of give explanations to already posted applications.
  • Include diagrams wherever possible
  • Include your Name in comments.
(1) Atomizer or sprayer
The common form of atomizer is shown in the fig. below
clip_image002
When the rubber bulb is squeezed, the air blows in the tube T with high speed .According to Bernoulli’s theorem a low pressure P2 is created inside T which is much less than atmospheric pressure P1 on the liquid surface in the vessel R. Due to it the liquid rises up in the tube T and is pushed out with air through nozzle N in the form of a spray. This principle is used in a paint sprayer, oil scent and nasal sprayer.
(2) Lift on an aeroplane wing
The shape of the aeroplane wing is peculiar. Its upper surface is
more curved than its lower surface and its leading edge is thicker than its trailing edge. As an aeroplane moves forward, the air blown in the form of stream lines over the wings of aeroplane is shown below.
As the upper surface of wing is more curved than its lower surface, therefore, the speed of air above the wings two is larger than the speed of the air below the wings. According to Bernoulli’s theorem, the pressure above the wings becomes less than that the pressure
below the wings. Due to this difference of pressure on the two sides of the wings, a vertical lift acts on the aeroplane. When this lift is sufficient to overcome the gravity pull on the aeroplane, the aeroplane is lifted up.
(3) Blowing off the roofs during storms
In a storm, the sometimes the light roofs of thatched houses are blown off.
This is because, a high velocity wind blowing over the roofs decreases, the pressure above the roof and therefore the greater atmospheric pressure below the roof lifts it up.
clip_image004
(4) Curved motion of spinning balls
(5) Motion of two parallel boats
(6) Bunsen’s Burner
In Bunsen’s burner, the gas escapes through the fine nozzle N with
a high velocity. It results in lowering of pressure in the neighbourhood of the nozzle. Due to decrease in pressure inside the burner, the atmospheric air enters through the holes HH. The air and the gas mixture rising up produce a flame, when ignited.
clip_image006
(6)A person standing near the railway track is pulled towards the train, when a fast moving train passes closes to him.
The fast train decreases the pressure between the person and the train. Due to the greater pressure on the other side of the person, the person gets pushed towards the railway track.
(7) Two ships sailing in the ocean get pulled towards each other, if they come closer to each other.
(8) Vacuum Brakes
Vacuum Brake is used to stop train in case of emergency.
In order to top train, the steam at pressure decreases and the piston of the brake
gets lifted, which through a mechanical system lifts the brake.




                    MORE  EXAMPLES FOR BERNOULLI’S THEOREM



One Problem, One Solution #1

Suppose that we have a series circuit with a supply of 150 V and three resistors: R1 = 330 ohms, R2 = 680 ohms, and R3 = 910 ohms. What is the power dissipated by R2?

 

SOLUTION

Find the current in the circuit. To do this, calculate the total resistance first.
Because the resistors are in series, the total is resistance is R = 330    +  680
  +   910 = 1920 ohms.

Therefore, the current is I = 150/1920 = 0.07813 A = 78.1 mA.

The power dissipated by R2 is P2 = I2R2 = 0.07813 x 0.07813 x 680 = 4.151 W


We must round this off to three significant figures, getting 4.15 W.

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BERNOULLI’s PRINCIPLE

In fluid dynamics, Bernoulli's principle states that for an inviscid flow, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy. Bernoulli's principle is named after the Dutch-Swiss mathematician Daniel Bernoulli who published his principle in his book Hydrodynamica in 1738.

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Bernoulli's principle can be applied to various types of fluid flow, resulting in what is loosely denoted as Bernoulli's equation. In fact, there are different forms of the Bernoulli equation for different types of flow. The simple form of Bernoulli's principle is valid for incompressible flows (e.g. most liquid flows) and also for compressible flows (e.g. gases) moving at low Mach numbers. More advanced forms may in some cases be applied to compressible flows at higher Mach numbers.

Bernoulli's principle can be derived from the principle of conservation of energy. This states that in a steady flow the sum of all forms of mechanical energy in a fluid along a streamline is the same at all points on that streamline. This requires that the sum of kinetic energy and potential energy remain constant. If the fluid is flowing out of a reservoir the sum of all forms of energy is the same on all streamlines because in a reservoir the energy per unit mass (the sum of pressure and gravitational potential ρ g h) is the same everywhere.

Fluid particles are subject only to pressure and their own weight. If a fluid is flowing horizontally and along a section of a streamline, where the speed increases it can only be because the fluid on that section has moved from a region of higher pressure to a region of lower pressure; and if its speed decreases, it can only be because it has moved from a region of lower pressure to a region of higher pressure. Consequently, within a fluid flowing horizontally, the highest speed occurs where the pressure is lowest, and the lowest speed occurs where the pressure is highest.

APPLICATIONS OF BERNOULLI’s PRINCIPLE

1. The carburetor used in many reciprocating engines contains a venturi to create a region of low pressure to draw fuel into the carburetor and mix it thoroughly with the incoming air. The low pressure in the throat of a venturi can be explained by Bernoulli's principle; in the narrow throat, the air is moving at its fastest speed and therefore it is at its lowest pressure.

A carburetor is a device that blends air and fuel for an internal combustion engine. It was invented by Karl Benz before 1885 and patented in 1886. It is colloquially called a carb. The word carburetor comes from the French carbure meaning "carbide". Carburer means to combine with carbon. In fuel chemistry, the term has the more specific meaning of increasing the carbon (and therefore energy) content of a fuel by mixing it with a volatile hydrocarbon.

clip_image004

2. The Pitot tube and static port on an aircraft are used to determine the airspeed of the aircraft. These two devices are connected to the airspeed indicator which determines the dynamic pressure of the airflow past the aircraft. Dynamic pressure is the difference between stagnation pressure and static pressure. Bernoulli's principle is used to calibrate the airspeed indicator so that it displays the indicated airspeed appropriate to the dynamic pressure.

A pitot tube is a pressure measurement instrument used to measure fluid flow velocity. The pitot tube was invented by the French engineer Henri Pitot in the early 1700s and was modified to its modern form in the mid 1800s by French scientist Henry Darcy. It is widely used to determine the airspeed of an aircraft and to measure air and gas velocities in industrial applications.

The basic pitot tube consists of a tube pointing directly into the fluid flow. As this tube contains fluid, a pressure can be measured; the moving fluid is brought to rest (stagnates) as there is no outlet to allow flow to continue. This pressure is the stagnation pressure of the fluid, also known as the total pressure or (particularly in aviation) the pitot pressure.

The measured stagnation pressure cannot of itself be used to determine the fluid velocity (airspeed in aviation). However, Bernoulli's equation states:

Stagnation Pressure = Static Pressure + Dynamic Pressure

Which can also be written

clip_image005

Solving that for velocity we get:

clip_image006

Where V is fluid velocity

and pt is stagnation or total pressure

and ps is static pressure

and ρ is fluid density

The dynamic pressure, then, is the difference between the stagnation pressure and the static pressure. The static pressure is generally measured using the static ports on the side of the fuselage. The dynamic pressure is then determined using a diaphragm inside an enclosed container. If the air on one side of the diaphragm is at the static pressure, and the other at the stagnation pressure, then the deflection of the diaphragm is proportional to the dynamic pressure, which can then be used to determine the indicated airspeed of the aircraft. The diaphragm arrangement is typically contained within the airspeed indicator, which converts the dynamic pressure to an airspeed reading by means of mechanical levers.

Instead of static ports, a pitot-static tube may be employed, which has a second tube coaxial with the pitot tube with holes on the sides, outside the direct airflow, to measure the static pressure.

Pitot tubes on aircraft commonly have heating elements called pitot heat to prevent the tube from becoming clogged with ice. The failure of these systems can have catastrophic consequences, as in the case of Austral Líneas Aéreas Flight 2553, Birgenair Flight 301 (investigators suspected that some kind of insect could have created a nest inside the pitot tube. The prime suspect is a species called the Black and yellow mud dauber wasp), Northwest Orient Airlines Flight 6231, AeroPeru Flight 603 (blocked static port), and of one X-31.

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