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1st year B.Tech Physics question bank

1st year B.Tech Physics Question Bank

This question bank  of ANU University is very much useful for the students of 1st year B.Tech.

Physics ( BT – 103 ) Question Bank  (One - mark questions)
Unit - I

 Q.1-What are Lissajous figures?
Ans: when two SHM’s are acting at right angles, the curve traced by the resultant of these two motions is called Lissajous figures. These Lissajous figures are more useful in determining the unknown frequency and phase of a vibration. It depends upon the following factors,
1.   Amplitude of the vibrations
2.   Frequency of the two vibrations
3.   Phase difference between the vibrations.
Q.2-What are ultrasonics?
Ans: The sound waves having frequencies above the audible range are known as ultrasonic waves [i.e>20kHz].
Define magnetostriction effect?
Ans: The change in dimensions of a ferromagnetic material by the application of a magnetic field is known as magnetostriction effect.
According to this effect, when a rod of iron or nickel is placed in a magnetic field parallel to its length a small extension or contraction occurs. This change in length is very small. Pure nickel, nickel Alloys (invar, monar metal, perm alloy) and cobalt ferrites are popular magnetostrictive materials.
Q.3 -What is piezo – electric effect?
Ans: If mechanical pressure is applied to one pair of opposite faces of certain crystals like Quartz, rochelle salt, tourmaline etc, equal and opposite charges appear on the other two perpendicular faces of the crystal.
Q.4- On which principle Piezo-electric ultrasonic generator works? What is it?
Ans: Piezo-electric ultrasonic generator works on inverse piezo-electric effect.
Inverse Piezo-electric effect:- When a voltage is applied across the opposite faces of a crystal, the crystal experiences mechanical deformation on the other two faces.
Q.5- Mention two engineering applications of ultrasonics?
Ans: (1) Cleaning and clearing. These waves can be used for cleaning utensils, washing clothes, removing dust and soot from the chimney.
   (2)Direction signaling. The ultrasonic waves can be concentrated into a sharp beam due to smaller wavelength and hence can be used for signaling in a particular direction.
  (3) Soldering and metal cutting. Ultrasonic waves can be used for drilling and cutting processes in metals. These waves can also be used for soldering; for example, aluminium cannot be soldered by normal methods. To solder aluminium ultrasonic wave along with electrical soldering iron is used. Ultrasonic welding can be done at room temperature
Q. What is Acoustic grating?
 Ans: When ultrasonic waves are propagated in a liquid, the density varies from layer to layer due to periodic variation of pressure. If under this condition, monochromatic light is passed through the liquid at right angles to the waves, the liquid behaves as a diffraction grating. Such a grating is known as acoustical grating.
Q. Calculate the natural frequency of iron rod of length 0.03m ( density of iron is 7.23 x 103 kg/ m3 and Young’s modulus is 11.6 x 1010 N/m2 )
Ans: n =     = 66.6 x 103 Hz
Q. What are coherent sources?
Ans: Two sources are said to be coherent if they emit light waves of same frequency, nearly same amplitude and are always in phase with each other.
In Young’s double slit experiment the intensity of central bright band is four  times the individual intensities of the interfering waves.
Q. Explain the principle of colours in thin films.
Ans: colours in thin films are formed due to the interference between light reflected from the two surfaces of a thin film.
What is Stoke’s principle of optical reversibility?
Ans: When light wave is reflected at the surface of an optically denser medium, it suffers a phase change of Π i.e., path difference of λ/2. No such phase change is introduced if the reflection takes place from the surface of a rarer medium.
Q. What is the principle of Michelson’s interferometer?
Ans: The amplitude of light beam from a source is divided into two parts of equal intensities by partial reflection & transmission. These beams are then sent in two directions at right angles & are brought together after they suffer reflection from plane mirrors to produce interference fringes.
Q. Mention two uses of Michelson’s interferometer?
Ans: i) It is used to measure extremely small distances like the expansions of small crystals under slight temperature changes.
ii) To measure the wavelength of the light emitted by a source.
Q. State two fundamental conditions for the production of interference fringes.
Ans:  I) The 2 sources must be very narrow.
   ii) The 2 sources must have equal intensities.
   iii) The 2 sources should have equal amplitude and frequency.
Q. What is meant by polarisation of light?
Ans: Confinement of vibrations of the electric vector to a particular plane along the direction of propagation of light wave is called polarization.
Q. State Brewster’s law.
Ans: The tangent of the angle of polarisation (p) is numerically equal to the refractive index (μ) of the medium.   i.e.,  μ = tan p
Q. Define the terms plane of vibration and plane of polarisation.
Ans: The plane in which vibrations take place is known as the plane of vibration. The plane, which is %u2534r to plane of vibration is known as the plane of polarisation.
Q. What is the path difference  between O – ray and E – ray in circular polarisation?
Ans: x = l /4
Q. What is a Nicol prism?
Ans: A Nicol prism is a rhomb of calcite crystal cut along the shorter diagonal & joined together with transparent cement called Canada balsam.
Q. What is optical activity?
Ans: The property of rotating the plane of vibration of plane polarised light about its direction of travel by some crystal is known as optical activity.
Those substances like quartz, sugar in solution, cinnabar etc., which rotate the plane of vibration (and also of polarisation) are known as optical active substances.
Q. Define double refraction.
Ans: When a ray of light is refracted by a crystal of calcite it gives two refracted rays. This phenomenon is called double refraction.
Q. Define Quarter – wave plate and Half- wave plate in the case of a Quartz crystal.
Ans: Quarter wave plate- It is a uniaxial doubly refracting crystal plate, cut with its axis parallel to the refracting faces, and can produce a phase difference of π/2 or a path difference of λ/4 between the ordinary and extra-ordinary rays.
Half wave plate - It is a uniaxial doubly refracting crystal plate, cut with its axis parallel to the refracting faces, and can produce a phase difference of π or a path difference of λ/2 between the ordinary and extra-ordinary rays.
Q. Distinguish between O- ray and E – ray.
Ans: The ray which obeys Snell’s law, is called Ordinary ray and the ray which do not obey Snell’s law is called Extraordinary ray. Velocity of O- ray is the same as that of the incident ray, while the velocity of E- ray depends on its direction of travel thru the crystal.
Intensity of light emerging from two crossed Nicol prisms is Zero
The two plane polarised light beams obtained from reflection by glass slab obey Brewster’s law. Then they are  perpendicular to each other.
Double refraction is due to anisotropic nature of the calcite crystal.
Q. What is Kerr effect?
Ans: An optically isotropic dielectric (solid, liquid or gaseous) may become optically anisotropic (doubly refracting) when subjected to an external uniform electric field. This phenomenon is known as Kerr effect.
Q. What is Faraday effect?
Ans: The optically in active substances are subjected to a magnetic field; they acquire the ability to rotate the plane of polarization of light propagated along the direction of the applied field. This is called Faraday effect.
Unit – II
Q. Define Electric flux. Write its SI units.
Ans: The scalar product of E and ds is known as the electric flux for the surface. Where E be the electric field acting on the surface.
    The total flux,  Ø = § E.ds = E.S
Q. Define Electric field and Electric field Intensity.
Ans : Electric field - The space surrounded by a charge upto which its influence is felt.
  Electric field Intensity  - Force per unit ve charge placed at a point, E = F/q
Q. State Gauss’s Law in electrostatics.
Ans: The total normal electric flux Ø over a closed surface is (1/ ε0) times the total charge Q enclosed within the surface. Mathematically it can be expressed as,   Ø = § E.ds = § E.ds Cos θ = (1/ ε0) Q
Where ε0 – permittivity of the free space.      Its value is  8.9 x 10-12 Coulomb2 / Nm2
Q. Define electric potential. Write its SI units.
Ans: It is defined as the work done in moving a unit ve charge from infinity to a point in an electric field.    SI Units – Volt
Q. Define capacitance. Write its SI Units.
Ans: The capacitance of a condenser is the amount of charge given to a conductor to rise its potential by unity.   C = q / V        Units : Coulomb / Volt    or    Farad.
Q. What is a Dielectric. What happens to the capacitance when a dielectric is placed in between two parallel plates.
Ans: Dielectrics are the substances, which do not contain free electrons. Ex – Glass, Plastic, etc.,
  The capacitance increases by a factor er when a dielectric is placed between the two parallel plates.
Q. Define Magnetic induction. Write its units.
Ans: The number of magnetic lines of force passing perpendicular to unit area.   Units: Tesla
Q. Define magnetic flux.
Ans: The total no. of lines of B that cut the surface.
Distinguish between electric lines of force and magnetic lines of force.
The electric force on a charged particle is always parallel to the lines of E but the magnetic force on a moving charged particle is always %u2534r to the lines of B.
The lines of E always begin and end at charges, while the lines of B always form closed loops.
3)    Electric lines of force do not exist inside a conductor but magnetic lines of force may exit inside a magnetic material.
Q. Electric lines of force never cross. Explain.
Ans: Because if they cross at a point, at the point of crossing it has two directions. It is not possible, so electric lines of force never cross.
Q. State Ampere’s law.
Ans: The line integral § B. dl for a closed curve is equal to μ0 times the net current i through the area bounded by the curve.  Thus § B. dl = μ0 i    where μ0 is the permeability constant,  μ0 = 4%u041F x 10-7  weber / amp – m
Q. State and explain Biot- Savart’s law.
Ans: The magnetic field dB at a point due to small element dl of a current carrying conductor is given by,       dB = μ0  i dl Sin θ
         4%u041F  r2
  The relation is called as Biot – Savart’s law.
 Where,    r  -  %u2534r distance of the point from the element dl.
    θ – angle between dl and r.
Q. Distinguish between Ampere’s law and Biot – Savart law.
Ans: Ampere’s law is applicable only for closed path. Where as Biot-Savart law is applicable to open paths also.
Q. Distinguish between Magnetic flux density and Magnetic field strength.
Ans:

Q. Write the SI units of Permittivity and Permeability.
Ans:  SI unit of Permittivity (e0)  –  C2 / Nm2     or    farad / m
   SI unit of Permeability (m0) – weber / amp-m   or   henry / m
Consider two parallel wires of 0.8m long and separated by a distance 0.02m. Due to a short-circuit a sudden current of 5000 amp. flows through the two wires. Q. What force will tend to pull the wires apart, assuming that the currents run oppositely?
Ans: F = μ0i1i2l / 2 %u041Fr     =>    F = 200 N.
A rectangular coil of sides 8cm and 6cm having 2000 turns and carrying a current of 20mA is placed in a uniform magnetic field of 0.2T directed along Ve X – axis. Q. What is the maximum torque, the coil can experience.
Ans: t = BiAN Cosq   ,  q=0   => t = 384 x 10-4
Q. What is Hall effect? Write its Physical Significance.
Ans: when a magnetic field is applied %u2534r to a current carrying conductor a potential difference is developed between the points on opposite side of the conductor.
Significance -  It gives information about the sign of charge carriers in electric conductor.
Q. Write the principle of Cyclotron.
Ans: It is based on the principle that a ve ion can acquire sufficiently large energy with a comparatively smaller alternating p.d. by making them to cross the same electric field & again by making use of a strong magnetic field.
 
Q. Can neutrons be accelerated in a cyclotron? Why?
Ans: No. A cyclotron can accelerate charged particles and is particularly suitable for protons and ve ions.
Q. Why is a cyclotron not suitable for accelerating electrons?
Ans: Electrons have very small mass. Even a small increase in the energy of the electron imparts a very high speed to it. Due to the high speed, the electrons go quickly out of step with the oscillating electric field.
Q. Explain the term inductance
Ans: The property of the circuit by virtue of which any change in the magnetic flux linked with it, induces an e.m.f. in it, is called inductance and the induced e.m.f. is called back e.m.f.
Q. Explain the term ‘ Induced Electric field’.
Ans:
State Faraday’s Law of electromagnetic Induction.
Ans: Following are the two laws of electromagnetic induction
When the magnetic flux linked with a circuit is changed, an induced e.m.f. is set up in the circuit.
The magnetic flux through any surface is defined as,
    f = ∫ B. dA     where, dA – element of area of the surface
If the magnetic field has a constant magnitude and direction over a planar area A, the flux can be written as,
    f =  BA Cosθ    where, θ – angle between the normal to the surface and the direction of the field.
The magnitude of induced e.m.f. is directly proportional to the negative rate of variation of magnetic flux linked with the circuit. If fB be the magnetic flux linked with circuit at any instant and e be the induced e.m.f. then,
e = - (dfB / dt )
  If there are N turns in the coil, then
e = - N(dfB / dt )
Q. State Lenz’s law.
Ans: The induced current in a closed conducting loop appears in such a direction that it opposes the change that produced it. The –Ve sign in Faraday’s law suggests this opposition.
Q. Distinguish between Self-induction and Mutual inductance.
Ans: When a current flows in a coil magnetic field is set up in it. If the current passing through the coil is changed, an induced e.m.f. is set up in the coil. The induced e.m.f. opposes any change of the original current. This phenomenon is called self induction.
    If two coils are placed near to each other as shown in fig. and a current is passed in the primary coil P, there is a change of magnetic flux linked with it, and an induced e.m.f. is set in the secondary coil S. this phenomenon is called mutual inductance.
Q. What is the basic cause of induced e.m.f?
Ans: Whenever magnetic flux linked with a coil changes, induced e.m.f. is produced.
Q. Self-induced e.m.f. is called Back e.m.f. Why?
Ans: It is because, the induced e.m.f. opposes the applied voltage.
Q. Write Maxwell’s equations.
Ans: The basic equations of electromagnetism are called Maxwell’s eq’s. The four fundamental eq’s are,
1) Gauss’ law for electricity   § E. ds = q / ε0
In differential form  =>   Ñ.E = r / ε0
2) Gauss’ law for magnetism   § B. ds = 0
In differential form  =>   Ñ.B = 0
 (3) Faraday’s law of induction   § E. ds = -dF / dt
In differential form  =>   Ñ x E  = - ÐB/ Ðt
 (4) Ampere’s law ( as extended by Maxwell )  § B. ds = m0i m0 ε0  dF/ dt
 In differential form  =>   Ñ x B  = m0 ( i   ε0  dF/ dt )
Q. State the modified Ampere’s circuit law.
Ans: Maxwell modified the Ampere’s law as,    § B. ds = m0i m0 ε0  dF/ dt   
Q. What are Electromagnetic waves?
Ans: The transverse time varying electric and magnetic fields propagating in space in a direction perpendicular to the direction of both the electric and magnetic fields are said to constitute electromagnetic waves.
Q. Write any two properties of Electromagnetic waves?
Ans:     i)  They are transverse in nature
ii)   do not require any material medium for propagation
iii)   travels with speed of light ( 3 x 108 ms-1) in vacuum.
Q. How do you determine the velocity of light from EM (Electromagnetic) theory?
Ans : C = 1/ √m0e0
Q. If the frequency of the a.c source in an LCR series circuit is increased, how does the current in the circuit changes?
Ans: With increase in frequency, current in a.c. circuit first increases, attains a maximum value (at resonant frequency) and then decreases.
Q. Why an LCR circuit produces damped oscillations?
Ans: An inductor possesses a small resistance also. Therefore, each time electric energy converts into magnetic energy, during LC – oscillations a small part of energy is dissipated as heat energy across the resistance of the inductor. As a result, the oscillations produced are damped in nature.
Q. When does a series LCR circuit have minimum impedance?
Ans: A series LCR circuit have minimum impedance at resonance

Unit – III
Q. What is a black body?
Ans: A blackbody is a body, which absorbs radiations of all wavelengths, incident upon it and emits them when heated. The radiations, which are emitted on heating, are known as black body radiations.
Q. Explain the failure of classical mechanics.
Ans: Classical mechanics failed to explain the following
The stability of the atom       2)  The spectrum of hydrogen atom
Thermal radiation of heated bodies     4)  Constancy of light velocity and
 5)    The origin of photoelectric effect.
Q. What is Planck’s hypothesis?
Ans: To explain the experimentally distribution of energy in the spectrum of black body, planck suggested that the energy of oscillating electrons is taken as discrete rather than continuous.
Q. What is meant by Compton effect.
Ans: When a monochromatic beam of high frequency radiation ( X-rays, g- rays etc.,) is scattered by a substance, the scattered radiation contains two components. One has a lower frequency or greater wavelength and the other having the same frequency or wavelength. This phenomenon is known as Compton effect.
Q. Explain Heisenberg’s principle with example.
Ans:    “It is impossible to know both the exact position and momentum of a particle simultaneously”
   If Dp is the uncertainty in determining the momentum and Dx is the uncertainty in determining the position of the particle then,
Dx. Dp  ³  h / 2P  
Q. What are matter waves.
Ans: The waves associated with the particles of matter ( ex. Electrons, protons etc.,) are known as matter waves or piolet waves or de Broglie waves.
Q. What led the discovery of matter waves?
Ans: de-Broglie’s consept of ‘nature loves symmetry ’ led to the discovery of matter waves.
Q. Explain the dual nature of matter.
Ans: Like radiations, matter also exhibits dual characteristic. For example light can act like wave sometime and like a particle at other times, then the material particles (ex. Electron, neutron etc.,) should act as wave at some other times.
Q. Explain the importance of Devission and Germer’s experiment.
Ans: The wave nature of the material particles as predicted by de- Broglie was confirmed by Davisson and Germer.
Q. State De-Broglie hypothesis
Ans: Like radiations, matter also exhibits dual characteristic. For example light can act like wave sometime and like a particle at other times, then the material particles (ex. Electron, neutron etc.,) should act as wave at some other times.
According to de – Broglie hypothesis, a moving particle is associated with a wave, which is known as de-Broglie wave.
Q. What is the physical significance of a wave function?
Ans: i) ‘Y’ measures the variations of the matter wave. So it converts the particle and its associated wave statistically.
ii)The wave function or complex displacement Y is a complex quantity and we cannot measure it.
iii)The matter wave can be represented by wave function. This wave function is used to identify the state of a particle in an atomic structure.
iv)It tells us where the particle is likely to be not where it is.
Q. If radiation has both particle and wave properties how can one decide which property to use in describing which Physical phenomenon.
Ans:
Q. What do you mean by radioactive element?
Ans: A radio active substance is one, whose atoms have unstable nuclei. The nuclei of radio active substances emit a, b and g rays.
Q. What is radio isotope?
Ans: The isotopes of an element, capable of emitting radiation just as radioactive elements do, are called radioisotopes.
Ex:-    6c11 &  6c13 are radio isotopes of 6c12
       11Na22& 11Na24 are radio isotopes of 11Na23
Q. Explain the principle of GM counter.
Ans: When a charged particle passes through the counter, it ionizes the gas molecules.
Q. Explain the concept of  “Fermi level”
Ans: The highest energy level, which an electron can occupy in the valence band at 0k is called Fermi level.
Q. Distinguish between conductors, semi conductors and insulators.
Ans:
Q. Define Fermi energy.
Ans: It is the average value of the highest of valence band energy and the lowest of conduction band energy.
      Ef = [Ec Ev] / 2
Q. Draw the characteristic curve of P-N junction diode.
Ans:

Q. Distinguish between energy levels and energy bands.
Ans:
Q. Distinguish between n- type and p- type semi conductors on the basis of energy diagram.
Ans:

Q. Distinguish between Intrinsic semiconductors and extrinsic semiconductors.
Ans: The semiconductors in its purest form are called intrinsic semiconductors.
  The impure semiconductors are called extrinsic semiconductors.
Q. What are Conduction band and Valence bands?
Ans:
Q. What is doping?
Ans: The process of adding impurity to a pure semiconductor is known as doping.
Unit – IV

Q. Distinguish between ‘Spontaneous emission and Stimulated emission’.
Ans:
 
Spontaneous emission   Stimulated emission     
1. Transition occurs from a higher energy level to a lower energy level.   Transition also occurs from higher energy level to lower energy level.     
2. No incident photon is required   Photon whose energy is equal to the difference of two energy levels is required.     
3. Single photon is emitted.   Two photons with same energy are emitted.     
4. The energy of emitted photon is equal to the energy difference of two levels.   The energy of the emitted photons is double the energy of stimulated photons.     
5. This was postulated by Bohr.   This was postulated by Einstein.   
Q. What is meant by Population Inversion?
Ans: The number of particles N2, i.e., population of higher energy level is less than the population N1 of lower energy level. Making the number of particles N2 more in higher energy level than the number of particles N1 in lower energy level (N2 > N1) is called as population inversion or inverted population.
What do you understand by Population inversion and Optic pumping?
Ans: The number of particles N2, i.e., population of higher energy level is less than the population N1 of lower energy level. Making the number of particles N2 more in higher energy level than the number of particles N1 in lower energy level (N2 > N1) is called as population inversion or inverted population.
The method of raising the particle from lower energy state to higher energy state is called as pumping. A more common method of pumping is optical pumping.
Q. Explain the principle involved in Laser construction.
Ans: Consider a group of atoms all in the same excited state. A passing photon may cause stimulated emission in one of these atoms. This results in the emission of two photons. Each of these photons may cause induced emission in two other excited atoms. This process may continue in a chain reaction. The result will be an intense beam of photons moving in the same direction and all are coherent.
Q. Name three important applications of Laser.
Ans: 1. lasers are used as the transmitters in optical communications over optical fiber and free space. They are used to store and retrieve data from compact discs and DVDs, as well as magneto-optical discs. Laser lighting displays (pictured) accompany many music concerts.
2. In science, lasers are employed in a wide variety of interferometric techniques, and for Raman spectroscopy. Other uses include atmospheric remote sensing, and investigation of nonlinear optics phenomena. Holographic techniques employing lasers also contribute to a number of measurement techniques. Lasers have also been used aboard scientific spacecraft.
3. In medicine, the laser scalpel is used for laser vision correction and other surgical techniques. Lasers are also used for dermatological procedures including removal of tattoos, birthmarks, and hair.
Q. What is an Optical fiber?
Ans: An optical fiber is a hair thin cylindrical tube of glass or any transparent dielectric medium for transmitting light.
Q. Define numerical aperture.
Ans: The Sine of the acceptance angle of an optical fiber is known as Numerical Aperture.
Q. How does an optical fiber transmit light?
Ans:
What is a fiber and define NA and acceptance angle?
Ans: An optical fiber is a hair thin cylindrical tube of glass or any transparent dielectric medium for transmitting light.
  The Sine of the acceptance angle of an optical fiber is known as Numerical Aperture.
  It may be defined as the maximum angle that a light ray can have relative to the axis of the fiber and  propagates down the fiber.
Q. Mention the different types of Optical fibers.
Ans: Optical fibers are in general of two types:
i) Single Mode Fiber (SMF)      and    ii) Multi Mode Fiber (MMF)
Write the applications of Optical fiber in Communications.
Ans:  As fiber communication has large bandwidth, the system is capable of handling a large number of  channels.
It is widely used in defense services because high privacy is maintained.
These are used for the transmission of digital data such as that generated by computers.
The military applications include communications; command and control links on ships and aircraft’s, data links for satellite earth stations.
It is used for signaling purposes.
Q. What is holography?
Ans: It is the process of image construction by recording and reconstruction by means of interference techniques without the aid of lenses.
Write two applications of holography.
Ans: 1. The most important applications of holography has been in interferometry.
  2.It can also be used for character recognition.
  3.This could be used to identify finger prints etc.,
  4.Holography techniques have been employed to produce gratings.
Q. What do you know about superconductivity?
Ans: A substance which conduct electricity without resistance is called a superconductor, the phenomenon is called superconductivity.
Ex: Silver, lead, gallium, iridium etc.,
What is Meissner effect?
Ans: The complete removal of magnetic field from the interior of superconductor is called Meissner effect.
Q. Distinguish between Type-I and Type-II superconductors.
Ans:
 
Type – I Superconductors   Type – II Superconductors     
1. These are Completely diamagnetic   These are Partially diamagnetic     
2. It exhibits complete Meissner effect.   It exhibits Meissner effect partially.     
3. These are Poor current carriers.   It Can carry heavy currents.     
4. It Cannot withstand strong magnetic field.   It Can withstand strong magnetic field.     
5. Ex: Aluminium, Tin, lead   Ex: Tantalum, Niobium   
Q. Which type of superconductor exhibit Meissner effect and explain what is it?
Ans: Type-II Superconductor exhibit Meissner effect.
The complete removal of magnetic field from the interior of superconductor is called Meissner effect.
Q. Mention two applications of superconducting materials.
Ans:
These are used in power generators.
Superconducting magnets have been used to raise the trains above the railway tracks and attain very high speeds.
These are used to launch the satellites into orbits directly from the earth without the use of rockets.
Superconducting rings can be used as a memory or a storage element in computers.
Q. Give examples of high temperature superconductors.
Ans: La-Sr-CuO4      ->   36 to 40k
  Y-Br-CuO3    ->  77k
  Y-Ba2-Cu3O7      ->   90k
  Lanthanum compounds  ->   300-500k
Q. Explain the principles of a photo diode.
Ans:
State the working principle of LED.
Ans: Energy is needed to create an electron –hole pair, and this energy is released when an electron & a hole recombine. In silicon & germanium the recombination energy is absorbed by the crystal as heat, but in certain other semi conductors like gallium Arsenide, a photon is emitted when recombination occurs. This is the basis of the LED.
Q. State the working principle of LCD.
Ans:
Q. Mention some applications of display devices.
Ans: i) visible LED’s are used as solid-state indicator lamps and as light sources for numeric & alphanumeric displays.
ii) Infrared LED’s are employed in optical fiber transmission.
iii) LED’s are used as status indicators in instruments, cameras, dashboards & computer terminals.
LCD:  1) Energy consumption is low   
2) It is very cheap   
3) It has very small thickness
Q. How solar energy is stored?
Ans:
What is a solar cell?
Ans: : A solar cell is basically a p-n junction diode, which converts solar energy (light energy) into electrical energy.
Q. How do you estimate the efficiency of a solar cell?
Ans:
Q. What are characteristics of a solar cell?
Ans:
Q. Define the critical parameters of a superconductor.
Ans: At the transition temperature the following changes are observed.
The electrical resistivity drops to zero.
The magnetic flux lines are excluded from the material.
There is a discontinuous change in specific heat
Further there are also small changes in thermal conductivity and the volume of the material.

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Comments (6)

sharath published on May 16, 2012, 05.49am IST

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hrithik143 published on Mar 29, 2011, 01.01pm IST

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zakaria published on Mar 23, 2011, 03.38am IST

sir

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sanjeeb published on Jan 14, 2011, 04.54am IST

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soumyamenonp published on Aug 06, 2010, 04.26pm IST

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vappu79 published on Jun 20, 2010, 02.46pm IST

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