Recent questions tagged class12

In an experiment of photoelectric effect , singly ionized helium is excited electronically to different energy levels. The emission spectra of helium produced is incident on a photo - electric plate in photocell .When helium is excited to fourth energy - level than the observed stopping potential of photocell is found to be five times stopping potential when hydrogen is excited to third level . Then the work function of material of photo-electric plate is

asked Feb 25, 2014 by yamini.v

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A laser is a coherent source because it contains:

asked Feb 25, 2014 by thanvigandhi_1

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The electromagnetic waves of frequency $2\: MHz\: to\: 30\: MHz$ are:

asked Feb 25, 2014 by thanvigandhi_1

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A gas of identical hydrogen like atoms has some atoms in lowest (ground) energy level A and some atoms in a particular upper (excited) energy , level B and there are no atoms in any other energy level . The atoms of gas make transition to higher energy level by absorbing monochromatic light photon having energy 2.7eV . Subsequently the atoms emit radiation of only six different photon energies . Some of emitted photons have energy 2.7eV some have energy more and some have less than 2.7eV . Then the principal quantum no .of initially excited level B is

asked Feb 25, 2014 by yamini.v

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The radio frequency $300\: MHz$ to $3000 \: MHz$ belong to:

asked Feb 25, 2014 by thanvigandhi_1

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An antenna is a device:

asked Feb 25, 2014 by thanvigandhi_1

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Which of the following is the disadvantage of FM over AM?

asked Feb 25, 2014 by thanvigandhi_1

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Which carboxylic acid will show HVZ reaction?

asked Feb 25, 2014 by sreemathi.v

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Consider the following statements \[\] Statement 1: A proton enters a strong magnetic field along the field direction. Its path and velocity remain the same\[\] Statement 2: The field exerts no force on the particle

asked Feb 25, 2014 by thanvigandhi_1

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A $\;^{118}cd\;$ radionuclide goes through transformation chain $\;^{118}Cd\; \to_{30 min}^{118}ln \to_{45 min} ^{118}Sn\;$(stable) The half lives are written below respective arrows ,A time t=0 only celuear present. Then the fraction of nuclei transformed into stable over 60 minutes:

asked Feb 25, 2014 by yamini.v

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Consider the following statements \[\] Statement 1: A magnetic field interacts with a moving charge and not with a stationary charge \[\] Statement 2: A moving charge produces a magnetic field

asked Feb 25, 2014 by thanvigandhi_1

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Consider the following statements \[\] Statement 1: The energy of a charged particle cannot change in magnetic field \[\] Statement 2: If the magnetic field does not change with time, there is no induced electric

asked Feb 25, 2014 by thanvigandhi_1

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In the below sequence of reaction X and Y are respectively

asked Feb 25, 2014 by sreemathi.v

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Consider the following statements \[\] Statement 1: The energy of a charged particle does not change in spatially varying magnetic field \[\] Statement 2: The instantaneous work done by magnetic field is zero

asked Feb 25, 2014 by thanvigandhi_1

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Consider the following statements \[\] Statement 1: The energy of a charged particle in a uniform magnetic field does not change \[\] Statement 2: Magnetic field does no work

asked Feb 25, 2014 by thanvigandhi_1

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Propionic acid $\quad \underrightarrow{PCl_3}\quad X\quad\underrightarrow{C_6H_6}\quad Y$.In this sequence Y is

asked Feb 25, 2014 by sreemathi.v

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Infinitely long wires parallel to the $y$ - axis are present in the $x-y$ plane at $x = 1, x = 2, x = 4$, and so on. The currents in all the wires with odd serial no is $1A $ in the $+y$ direction while it is $1A$ in the $–y$ direction for all the wires with even serial no. The magnetic field at the origin would be

asked Feb 25, 2014 by thanvigandhi_1

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Masses of two isobars $\;_{29}^{64}Cu\;$ and $\;_{30}^{64}Zn\;$ are 63.9298n and 63.9292n respectively.It can be concluded from these data that

asked Feb 25, 2014 by yamini.v

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A straight wire of length $\ell$ carries a current $i$. The magnitude of magnetic field at the point $P$ is

asked Feb 25, 2014 by thanvigandhi_1

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The two cleavage reactions are given below :

asked Feb 25, 2014 by sreemathi.v

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The below reaction with (i) $NH_3,H_2O$,(ii) acid HCl respectively give

asked Feb 25, 2014 by sreemathi.v

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In the following reaction the structure of the major product X is

asked Feb 25, 2014 by sreemathi.v

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A monochromatic radiation wavelength $\;\lambda_{1}\;$ is incident on a stationary atom as a result of which wavelength of photon after collision becomes $\;\lambda_{2}\;$ and recoiled atom has De- Broglie's wavelength $\;\lambda_{3}\;$.Then

asked Feb 25, 2014 by yamini.v

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Which of the following is the major product of the reaction shown below

asked Feb 25, 2014 by sreemathi.v

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The ratio of de-Broglie wavelength of moleculus of hydrogen and helium in two gas jars kept separately at temperatures $\;27^{0} C\;$ and $\;127^{0} C\;$ respectively is

asked Feb 25, 2014 by yamini.v

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A metal M(at.wt = 40.0) depending on temperature crystallises in f.c.c and b.c.c structure whose unit cell length are 3.5 and $3.0 A^{\large\circ}$ respectively. The ratio of its densities in f.c.c and b.c.c structures is

asked Feb 25, 2014 by sharmaaparna1

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The ratio of de-Broglie wavelength of a $\;\alpha\;$ particle to that of proton being subjected to same magnetic field so that the radii of their path are equal to each other assuming the field induction vector $\;\overrightarrow{B}\;$ is perpendicular to velocity vectors of $\;\alpha-\;$ particle and proton , is

asked Feb 25, 2014 by yamini.v

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A unit cell of NaCl has four formula units. The edge length of unit cell is 0.564. The density of NaCl is

asked Feb 25, 2014 by sharmaaparna1

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A chiral $C_5H_{10}O$ ether reacts with hot $HI$ to give a $C_5H_{10}I_2$ product.Treatment of this with hot $KOH$ in ethanol produces $1$,$3$-pentadiene.What is the structure of the original ether?

asked Feb 25, 2014 by sreemathi.v

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At room temperature , Sodium crystallizes in a b.c.c lattice with edge length $a = 4.24A^{\large\circ}$ . Find the theoretical density of sodium.

asked Feb 25, 2014 by sharmaaparna1

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If a stationary electron gets annihilated due to association with a stationary positron (hypothetically), the wavelength of resulting radiation will be .

asked Feb 25, 2014 by yamini.v

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Which of the following is expected to have the lowest boiling point?

asked Feb 25, 2014 by sreemathi.v

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The density of KBr is 2.73g/cm. The length of the unit cell is 654pm. Find the number of atoms per unit cell in the cubic structure.

asked Feb 25, 2014 by sharmaaparna1

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Acid-catalysed reaction of oxirane is given below:

asked Feb 25, 2014 by sreemathi.v

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In CsCl with cubic structure $Cl^-$ ions are located at each corner and $Cs^+$ ions at the centre of the unit cell. If $r_{Cs^+}$ and $r_{Cl^-}$ are $1.69A^{\large\circ}$ and $1.81A^{\large\circ}$ respectively . Find the value of edge length of cube.

asked Feb 25, 2014 by sharmaaparna1

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When a metallic surface is illuminated with monochromatic light of wavelength $\;\lambda\;$ and stopping potential for photo electron current is $\;3V_{0}\;$ . When some metallic surface is illuminated with a light of wavelength $\;2 \lambda\;$ , The stopping potentials is $\;V_{0}\;$ . The threshold wavelength for surface is

asked Feb 25, 2014 by yamini.v

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In the below reaction product is/are

asked Feb 25, 2014 by sreemathi.v

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A photon of wavelength $\;5030 A^{0}\;$ is incident on a totally reflecting surface. The momentum delivered by photon is equal to

asked Feb 25, 2014 by yamini.v

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The formation of peroxide linkage in either due to the exposure in air can be detected by treating in with

asked Feb 25, 2014 by sreemathi.v

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What are the resulting products of the reaction below?

asked Feb 25, 2014 by sreemathi.v

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A star initially has $\;10^{40}\;$ deutrons . If produces energy via the process $\;_{1}H^{1}+_{1}H^{2} \to _{1}H^{3}+P\;$ and $\;_{1}H^{2}+_{1}H^{3} \to _{2}He^{4}\;.$ If the average power radiated by star is $\;10^{16}W\;,$ the deutron supply of star is exhausted in a time of order of \[\] (The masses of nuclei are $\;m(H^2)=2.014\;amu\;,m(p)=1.007 amu , \; m(n)=1.0084 amu ,\; m(H)=4.001 amu))$

asked Feb 25, 2014 by yamini.v

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What would be the product in the following reaction:

asked Feb 25, 2014 by sreemathi.v

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Which of the following reaction is the best choice for preparing Ethyl phenyl ether?

asked Feb 25, 2014 by sreemathi.v

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The following ether,when treated with HBr produces

asked Feb 25, 2014 by sreemathi.v

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Which of the following statement is correct?

asked Feb 25, 2014 by sreemathi.v

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Williamson ether systhesis for tert-butyl methyl ether is

asked Feb 25, 2014 by sreemathi.v

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The major product formed on the reaction given below :

asked Feb 25, 2014 by sreemathi.v

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Binding energy per nucleon vs mass no . Curve for nuclei is shown in figure. W,X,Y,Z are four nuclei indicated on curve . The process that would release energy is

asked Feb 24, 2014 by yamini.v

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The weight based ratio of $\;U^{238}\;$ and $\;Pb^{226}\;$ in a sample of rock is 413 . if the half life of $\;u^{238}\;$ is $\;4.5 \times10^{9}\;years \;,$ then age of rock is

asked Feb 24, 2014 by yamini.v

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A hydrogen atom is in an excited state of principal quantaum number$\; (n)\;$ it emits a photon of wavelength $\;(\lambda)\;,$ when it returns to ground state . The value of n is

asked Feb 24, 2014 by yamini.v

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