8/13/2019 Assignment No 7 Dual Nat,Atoms and Nuclei

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Assignment 7

Dual nature of matter, Atoms and NucleiGUIDE LINE FOR PREPARING CBSE P!"SICS# E$A%INA&ION &!ROUG!

PRE'IOUS "EARS (UES&IONS OF CBSE

%AR)ED *I&! S&ARS #

1. Diagrammatically show the spectral series of hydrogen atom. Also give the limitations of Bohrs theory.***

2. State Bohrs theory of the spectrum of hydrogen atomic spectra. Hence otain an e!pression for radius of

orit and the energy of orital electron in hydrogen atom.**". #ame the series of hydrogen spectrum which lies in the visile region of electromagnetic spectrum$**

%Ans&Balmar series lies in visile region'

(. #ame the series of hydrogen spectrum which lies in the ) regopn$** %Ans& +ymen series lies in ).region',. #ame the series of hydrogen spectrum which lies in the infrared region of electromagnetic spectrum$**

%Ans&-aschen series Brac/ett series an -fund series.'

0. he ioniation potential of hydrogen is 1".0 volt .3alculate the energy of its first e!cited state. **%Ans& 4"., ev5. he energy of an electron in nthorit is given yE6 4 1".07 n2 eV. 3alculate the energy re8uired to ta/e and

electron from ground state to the second e!cited state.**** %Ans& 12.9: ev'

;. -rove that energy is 8uantied in an atom. ive the circuit diagram for studying photoelectric effect. Draw

the four sets of characteristic curves related to photoelectric effect and write the important conclusions that

you draw form these curves$ =rite ?insteins photoelectric e8uation and use it to e!plain the @i

independence of ma!imum energy of emitted photoelectrons from intensity of incident light and @ii

e!istence of threshold fre8uency for a given photo4sensitive surface.How you can determine the

value of -lan/s constant.

An electromagnetic wave of wavelength is incident on a photosensitive surface of negligile wor/

function. f the photo4electrons emitted form this surface has the de4Broglie wavelength 1 prove that =

@2mc/h12

19. Derive the e!pression for the de4Broglie wave length of an electron moving under the potential difference ofVvolt. =hat will e the de4Broglie wavelength when the accelerating potential is increased to ( V.

An electron an alpha particle and a proton have the same /inetic energy. =hich one of these particles has @i the

shortest and @ii the largest de4Broglie wavelength$

An electron and alpha particle have the same de4Broglie wavelength associated with them. How are their /inetic

energies related to each other$

=ith what purpose was famous Davission4>ermer e!periment with electrons performed$ Descrie Davisso

and >ermers e!periment to demonstrate the wave nature of electrons. Draw a laeled diagram of apparatus

used.

11. =hat will e the ratio of radii of two nuclei of mass numersA1andA2.**3ompare the radii of two nuclei with mass numers 1 and 25respectively.**%Ans.17"'

=hat is the nuclear radius of 125Feif that of 27Al is ".0 fermi$** %Ans&0.9 fermi'

Assuming the nuclei to e spherical al in shape how does the surface area of a nucleus

of mass numerA1compare with that of a nucleus of mass numerA2.**

12. =hat is the ratio of nuclear densities of the two nuclei having mass numer in the ratio 1&(.******%Ans& #ucleadensity is independent of mass numer so this ration is 1&1'

1". State three properties of nuclear forces. Show that the density of nuclear mater is independent of mass

numerA.

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Draw a graph showing the variation of potential energy etween a pair of nucleons as a function of their

separation. ndicate the regions in which the nucleus for is @i attractive and @ii repulsive.

1(. Descrie Cutherford scattering e!periment. =hat are its oservations and conclusion$

Derive an e!pression for the distance of closest approach in Cutherfords 4scattering e!periment and then

calculate its value of 4particle and gold nucleus.

1,. Draw a diagram to show the variation of inding energy per nucleon with mass numer for different nuclei.

=rite conclusions drawn from the graph.Also e!plain fission and fusion on its asis$

3alculate the inding energy per nucleon of 26Fe56.%>iven& m(26Fe

56)6 ,,.:"(:"2 amum(neutron6

1.99;0;, amu m(proton6 1.995;2, amu '

10. Distinguish etween isotopes and isoars.>ivce one e!ample for each of the species.**15. he radioactive isotopeD4decays according to the se8uence.

- Particle - particle

D D1 D2f the mass numer and atomic numer of are 150 and 51 respectively what is the @i

mass numer and @ii atomic numer ofD$***** %Ans A61;9 and E6 52'

1;. A radioactive isotopeDdecays according to se8uence.

D D1 D2 f the mass numer and atomic numer of D2 are 150 and 51 respectively find the mass

numer and atomic numer ofD.Amongst.D , D1 and D2 do we have any isoars or isotopes$*** %Ans A61;1 and E6 5"the mass numer ofDis 1;1 and atomic numer 5".3learlyDD1 are isotopes

1:. n radioactive decay as follows

A A1 A2 he mass and atomic numers ofA2are 150 and 51 respectively what are the mass

numers and atomic numers of A1andA.=hich of these elements are isoars.**%Ans he mass numer ofA1andAare 1;9 each. he atomic numers of A1andAare 5" and 5(

respectively. he elementsA1andAare isoars are isotopes.'

29. A radioactive nucleus A undergoes a series of decay according to the following scheme& - Particle -particle - particle - particle

A A1 A2A3A4

he mass numer and atomic numer ofAare 1;9 and 52 respeciely.=hat are these

numers forA4.**%Ans he mass numer ofA4 is 152 and atomic numer is 0:'

21. =rite the laws of radioactive disintegration. -rove&N6No e-t. S/etch a graph to illustrate the radioactive

decay.

Define the terms half life period and decay constant of a radioactive sustance.

)sing e!ponential decay law otain the formula for the half4life of a radioactive nuclide in terms of it

disintegration constant. *****

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Find out an e!pression for mean life time.

Define the term Activity of a radioactive sustance. State its S unit. >ive a plot of activity of a

radioactive species versus time.

=hat is activity of radioactive sustance prove thatA6Ao e-t

Show that the decay rateR of a sample of radioactive nucleiNat the same instant can e e!pressed as

R = N.

-rove that the instantaneous rate of change of the activity of a radioactive sustance i

inversely proportional to the s8uare of its half life22. Define the )nits& @i 3urie *@ii Cutherford **and @iii Bec8uerel*.@iv Fermi*

2". A radioactive isotope has a half4life of , years. After how much time is its activity reduced to ".12,G of its

original activity$ (CBSE 2008) %Ans& 2, yrs'2(. ?!plain the terms& @i 3ritical sie** @ii hermal neutrons** @iii odulator @iv 3ontrol rod **and @v

coolant.**

2,. State reason why heavy water is generally used as a moderator in a nuclear reactor.

#ame the asoring material used to control the reaction rate of neutron in a nuclear reactor.**