Wednesday, March 21, 2012


Physics Lab Viva Voce Questions and its answers Laser Parameters
1. What is semi conductor diode laser?
Semiconductor diode laser is a specially fabricated pn junction diode. It emits laser light when it is
forward biased.
2. What is LASER?
The term LASER stands for Light Amplification by Stimulated Emission of Radiation. It is a device
which produces a powerful, monochromatic collimated beam of light in which the waves are coherent.
3. What are the characteristic of laser radiation?
Laser radiations have high intensity, high coherence, high monochoromation and high directionality
with less divergence.
1.What is meant by interference of light?
When the two waves superimpose over each other, resultant intensity is modified. The modification in
the distribution of intensity in the region of superposition is called interference.
2.Is there is any energy loss in interference phenomenon?
No, there is only redistribution of energy ie, energy from dark places is shifted to bright places
3.What are interference fringes?
They are alternately bright and dark patches of light obtained in the region of superposition of two wave
trains of light.
1.what is plane transmission diffraction grating?
A plane transmission diffraction grating is an optically plane parallel glass plate on which equidistant,
extremely close grooves are made by ruling with a diamond point.
2. In our experiment. What class of diffraction does occur and how?
Fraunhofer class of diffraction occurs. Since the spectrometer is focused for parallel rays, the source
and the image are effectively at infinite distances from the grating.
3. How are the commercial gratings are made?
A commercial gratings is made by pouring properly diluted cellulose acetate on the actual grating and
drying it to a thin strong film. The film is detached from the original grating and is mounted between
two glass plates. A commercial grating is called replica grating. In our experiment we use plane type
replica grating.

A wave is a phenomenon whereby energy is moved without the transference of any material. X-rays, ultraviolet rays, light and radio waves all travel at the same speed through a vacuum. Examples of waves include water waves, sound waves, light and X-rays. There are two main types of waves: transverse and longitudinal. In transverse waves the vibrations are perpendicular to the direction of travel, whereas in longitudinal waves the vibra tions are parallel to the direction of travel.
WAVE LENGTH AND FREQUENCY                                                                                                                                                                                        The distance between successive wave crests is called the wavelength, X (lamda). The frequency (f) of a wave is defined as the number of complete oscillations per second. Frequency is measured in hertz (Hz). Audible sound frequencies range from 20 Hz (a low rumble) to about 20,000 Hz (a shrill whistle). The speed of a sound wave in air at 20°C (68°F) is 344 m/s, but in water sound travels at 1461 m/s and in steel its speed is 5000 m/s.
PROPERTIES OF WAVES                                                                                                                                                                                                                                                                 Waves have several properties, including reflection, refraction, diffraction and interference.
Reflection is the process whereby part or all of a wave is returned when it encounters the boundary between two different materials or media. Important example of a wave reflection is an echo, when sound waves bounce off a faraway surface.
Refraction Refraction is the change of direction of a wavefront as it passes obliquely (at any angle which is not perpendicular or parallel) from one medium to another in which its speed is altered. An example is when light enters a lens or prism – the light is bent. It is the principle of refraction that makes the lenses in spectacles work.
Diffraction occurs when waves passing through a slit which is narrow compared to the wavelength are spread out and depart from the expected straight line direction. This explains how we can hear the words of someone who is facing away from us.
Interference is the phenomenon that occurs when two or more waves combine together as dictated by the principle of superposition. The superposition principle states that when two waves are in the same place at the same time, their amplitudes (heights) are combined. If  the resultant wave amplitude is greater than that of the individual waves then constructive interference is taking place. If the resultant wave is smaller, then destructive interference is taking place.
Electromagnetic waves are caused by a mutual fluctuation in electric and magnetic fields. All the properties of sound and water waves, such as refraction and diffraction, exist in electromagnetic waves, but they differ in that they are able to transmit energy in a vacuum. They travel extremely fast: at 299,792,458 m/s in a vacuum. Electromagnetic waves include light, microwaves,  infrared radiation and X-rays. The electromagnetic spectrum is the collective set of waves over a broad range of wavelengths, from gamma waves (wavelength 10-16 m) to radio waves (wavelength 103 m).

When a red hot piece of iron cools down, it transfers energy to its surroundings in three possible ways: conduction, convection or radiation.
Heat conduction occurs when kinetic and molecular energy pass from one molecule to another. Metals are good heat conductors because of electrons that transport energy through the material.
Heat convection results from the motion of the heated substance. Convection is the main mechanism for mixing the atmosphere and diluting pollutants emitted into the air.
Radiation All bodies radiate energy in the form of electromagnetic waves. Radiation may pass across a vacuum, and thus the Earth receives energy radiated from the Sun. A body remains at a constant temperature when it both radiates and receives energy at the same rate.
The interactions between matter can be explained by four forces:
Gravitational: The weakest of the four forces, the gravitational force is the mutual attraction between masses. Although its effect is small in the realm of subatomic particles, it has great cosmic power, and is the force that holds solar systems and galaxies together.
Electromagnetic: This force explains the magnetic field and the electron-nucleus structure of an atom.
Strong: Some 100 times stronger than the electromagnetic force, the strong force holds together the protons and neutrons within an atomic nucleus.
Weak: This force is associated with the radioactive beta-decay of some nuclei. The electromagnetic and weak forces have recently been shown to be part of an electro-weak force.
Gases:  Gases are readily compressible by a factor up to one thousand, showing that there must be large spaces between the molecules. The molecules in a gas are able to translate (move freely), rotate and vibrate. The temperature of a gas is a measure of the average kinetic energy of its molecules.
Liquids:  Liquids are not easily compressible. Liquids are much more dense than the corresponding gases from which they are condensed. In a liquid the molecules are in contact with each other, yet able to move around as the molecules vibrate and disturb each other.
Solids:  Solids are not at all easily compressible. In a solid the particles vibrate ever more vigorously as the temperature is raised.
Motion And Mechanics KINEMATICS
Kinematics covers a broad range of topics, from bodies falling to earth, to the description of bodies moving in a straight line, to circular motion.
Speed Speed is the ratio of a distance covered by a body in a given amount of time, to that time. It is measured in metres per second.
Velocity velocity is speed measured in a particular direction. Velocity is a vector quantity, which is one in which both the magnitude and direction are stated.
Acceleration and Deceleration
Acceleration is the rate of change of velocity. Acceleration may be defined as the change in velocity over a given time interval. Acceleration is measured in m/s2 (or ms-2).
Newton’s three laws of motion state the fundamental relationships between the acceleration of a body and the forces acting on it.
1. A body will remain stationary or travelling at a constantvelocity unless it is acted upon by an external force. Newton’s first law explains why we lurch forward in a car when it suddenly breaks, and why we are pushed back into our seats when a car suddenly accelerates.
2. The resultant force exerted on a body is directly proportional to the acceleration produced by the force. 
The second law of motion can be expressed in an equation: force = mass x acceleration, or F = ma. Forces are measured in newtons. A force of 1 newton will accelerate a mass of 1 kg by 1 m/s2.
3. To every action there is an equal and opposite reaction. When a bullet is fired, thegun recoils backwards. This is caused by a reaction force on the gun from the bullet. From this law can be derived the principle of the conservation of momentum. Momentum, which Newton called the ‘quantity of motion’, is the product of mass and velocity.
According to this law every particle in the universe attracts every other particle in the universe. Newton’s Law of Gravitation is thus: F = Gm1m2/r2, where G is the ‘universal gravitational constant’. Further experiments on gravity proved that: G = 6.67206 x 10-11 Nnr-2kg-2.
Measurement Units
Acre: A measure of land, 4,840 square yards (4,046 square metres).
Ampere: Unit for measuring the strength of an electric current. It is the amount of current sent by one volt through a resistance of one ohm.
Angstrom: It is the unit for measuring the wavelength of light. It is one hundred-millionth of a centimetre.
Astronomical unit: A unit of length equal to the mean radius of earth orbit. It is 149,597,870 km (92,955,800 miles).
Bar: Unit of atmospheric pressure. One bar is equal to a pressure of 106 dynes per sq cm.
Barrel: For measuring liquids. One barrel is equal to 31.1/2 gallons in US and 36 imperial gallons in Britain.
Bushel: Unit of dry measure for grain, fruit, etc. It is equal to 4 pecks or 8 gallons.
Calorie: Unit for measuring the amount of heat required to raise the temperature of one gram of water through 1°C. It is used as the unit for measuring the energy produced by food when oxidised in the body.
Carat: Unit of weight for precious stones and pearls. It is equal to about 3.17 grains troy or .2 of gram. It is also a measure of the purity of gold alloy indicating how many parts out of 24 are pure.
Coulomb: Unit for measuring the quantity of an electric current. It is the amount of electricity provided by a current of one ampere flowing for one second.
Decibel: Unit for measuring the volume of sound. It is equal to the logarithm of the ratio of the intensity of sound to the intensity of an arbitrarily chosen standard sound.
Dyne: Amount of force that causes a mass of one gram to alter its speed by one centimetre per second for each second during which the force acts. This unit of force is in CGS (metric) system.
Erg: Unit of work or energy in CGS (metric) system. It is the amount of work done by one dyne acting through a distance of one centimetre.
Farad: Electromagnetic unit of capacitance. It is equal to the amount that permits the storing of one coulomb of charge for each volt of applied potential difference.
Fathom: Unit for measuring the depth of water or the length of a rope or cable. One fathom is equal to 6 feet.
Gallon: It is a measure of liquid.
Gross: 12 dozens or 144.
Hertz: Modern unit for measurement of electromagnetic wave frequencies.
Horse power: Unit for measuring the power of motors or engines. It is equal to a rate of 33,000 foot-pounds per minute, i.e., the force required to raise 33,000 pounds at the rate of one foot per minute. HP = 746 watts
Modern physics sees heat as energy collectively possessed by the particles making up a gas, liquid or solid. A body which possesses energy has the ability to do work. Work is done when a force (F) moves through a distance (d): W = F x d. If F is measured in newtons and d in metres, then W is measured in Nm, otherwise called joules.
Thermodynamics is the study of the behaviour and properties of heat, energy and temperature within systems.
The first law of thermodynamics
The first law of thermodynamics states that the total amount of energy in any closed system always remains the same. In other words, energy is always conserved as it is transferred from one form to another.
The second law of thermodynamics
The second law of thermodynamics states that heat will always flow from a hotter object to a colder one, and not the other way round. It involves the term entropy. Entropy is a measure of the disorder of a system.
The third law of thermodynamics
The third law states that on approaching absolute zero, extracting energy from a system becomes increasingly harder. All bodies have thermal energy, or heat. Absolute zero is the theoretical point at which a body ceases to have any heat. This value is -273.15°C (-459.67°F) or 0°K (Kelvin). At this temperature, which is impossible to physically attain, the molecules in a body will cease to vibrate, and thus the body will have no internal energy.
Electromagnetism is the study of the effects caused by stationary and moving electric charges.
Pieces of some metallic ores, such as lodestone, are magnetic when suspended freely from a thread they point north-south.Such magnetic compasses have been used since 500 BC.
At present, science recognises a spectrum of electromagnetic radiation that extends from about 10-15 m to 10° m.
Radio waves have a large range of wavelengths, from a few millimetres up to several kilometres.
Microwaves are radio waves with shorter wavelengths, between 1 mm and 30 cm, and are used in radar and microwave ovens.
Infrared waves of different wavelengths are radiated by bodies at different temperatures. The Earth and its atmosphere, at a mean temperature of 250 K (-23°C or -9.4°F) radiates infrared waves with wavelengths centred at about 10 micrometres.
Visible waves have wavelengths of 400-700 nanometres (nm; 1 nm = 10-6 m). 
Ultraviolet waves have wavelengths from about 380 nm down to 60 nm. The radiation from hotter stars, above 25,000°C (45,000°F), shifts towards the violet and ultraviolet  parts of the spectrum 
X-rays have wavelengths from about 10 nm to 10-4 nm.
Gamma rays are emitted by certain radioactive nuclei in the course of nuclear reactions. It is now known that the Earth itself has magnetic properties. An important feature of a magnet is that it has two poles, one of which is attracted to the Earth’s magnetic North Pole, while the other is attracted to the South Pole.
Static electricity involves electric charges at rest. In 1785, Coulomb formulated the Law of Attraction and Repulsion between electrically charged bodies: F=kQ1Q2/r2 where F is the force, k is a constant, Q1 and Q2 are the sizes of the charges (+ or -), and r is the distance between the charges.
Matter can exist in three states - solid, liquid or gas (vapour). Virtually all substances are able to exist in more than one of these three states. Water is a liquid at room temperature, for example, but can become a solid (ice) or vapour (steam), depending upon  temperature and pressure.

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