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.
AIR WEDGE
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.
SPECTROMETER GRATING
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.
WAVES
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
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
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
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
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).
THE
KINETIC THEORY OF MATTER
When a
red hot piece of iron cools down, it transfers energy to its surroundings in three
possible ways: conduction, convection or radiation.
Conduction
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.
Convection
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 FOUR FUNDAMENTAL FORCES
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.
STATES OF MATTER
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
LAWS OF MOTION
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.
NEWTON’S
LAW OF GRAVITATION
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
HEAT AND WORK
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
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
Electromagnetism is the study
of the effects caused by stationary and moving electric charges.
MAGNETISM
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.
ELECTROMAGNETIC
SPECTRUM
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
ELECTRIC CHARGES
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.
STATES OF MATTER
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.
