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UGC CSIR NET 2012 December 23 Answer Key Comment here with explanation

 Question paper and Key

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1. partc:uncertainity in momentum question:ans was square root h/2mw....is it correct?

2. This comment has been removed by the author.

3. It is definitely squre root of h/2mw

4. right. there is a square root...

2. i think it ws sq root h/4mw

3. 2by2 unitary matrix with det exp(imphi) to be converted to matrix with det 1?
multiply a row or column by exp(-imphi)

chemical potential for Bose Einstein condensation...is it zero?

unit normal vector to given equation of eclipse?

2. yeah it was zero 100 percent right for boson gas

3. the chemical potential for boson is -Ve

4. Zero is exactly right...

5. i think its 1/2 hw because in case of HO ground state energy is not 0. In case of BEC chemical potential is lowest eigenvalue (energy)

6. But there is also a condition for BEC . chemical potential value is less than ground state energy value ...

4. a thermodynamic process occurs by 2 ways-AtoC and AtoB toC.amount of heat in 2nd...is answer 80J?

life time of particles in decreasing order...p,n,pie,delta?

1. energy extract is 80 j

2. i think 220 J

3. I think 80j

4. internal energy is path independent but both work done and heat are path dependent quantities . with this in mind first calculate internal energy using formula dQ=dU+dW . then with that internal energy calculate dQ .
I didnt remember the exact value. I too think 80j

5. section-A
length of pavement-300m
graph for dis covered by snail-D choice..the graph with negative slope.
length on earth of river in semicircle...11km
rectagular figure...distance PQ=15/4
area of triangle?
smallest number exp(-1/exp)or .33^.33 or .44^.44or pie^(x-1/pie)

1. graph for dis covered by snail-C choice..time will not be go back

3. yes snail-C time will not go back

4. Sure, C is correct

5. D is right

6. D( having pi's)

7. yes answer c is correct time cant be decreased

]

6. minimum days between fridays 13 to 13....28

1. In leap year it won't be 28.

2. no it is 91 days including leap year

3. yes..91 days is the right answer.

4. I think it would be 56 days

5. definitely answer is 91 days

6. Start from 13th January Friday. You will reach 13th April Friday with February 29 days. So 91 days.

7. 91 as it is a common factor of 7 and 13

7. unit normal is option D I+J+K/sq3..because its a special case whn a=b=c u have to take this one

1. was that mention in the question that a=b=c??? i didn't remember .

2. in unit normal vector it will be option A....you have to take gradient and then satisfy the points given...u will get option A.

3. procedure is correct.

8. the ratio between triangle area is 1:2
hexagonal problm is sq2*a
25%of25% 0f x where x ix6.25%
cucumber is 99kg

1. you are correct

2. cucumber 50 kg

3. cucumber : 50kg is the right answer

4. 1:3, sq2*a, 6.25 , 99kg

5. 1:2,sq(2)*a,6.25,99kg

6. cucumber problem...

first water 99% others 1% total weight 100kg... ie 99kg water 1 kg others

after 30 days water 98% and others 2%...
1 kg others remains same till now
so suppose x is the total weight now
ie 2% of x is 1 kg
x * 2/100 = 1
x=100/2 =50kg

right...??

7. yeah ur right

8. 1:2 is correct...100%

9. part B harmonic oscilator problm with (a-x) ans is (n+1/2)hw+1/2aw2....u have solve it exactly this is the total correction..obviously those who calculate 1st order correction they must argue that ans =(n+1/2)hw but they asked total correction either if u do it by quantum mechanically u hv to go upto 2nd order...(Zetly quantum mechanics)

1. but expectation value of x operator is zero so this part will not contribute what i think/

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3. if you do 2nd order PT you will get non zero term...i think

4. i think no effect of perturbation

10. logic gate choice is A.B whole bar

1. yup whole bar A.B

2. This comment has been removed by the author.

3. it is A+ B

4. No it is A.B whole bar.

5. No doubt..A.B whole bar..

11. modulation problem answer is 6.99 MHz to 7.01 MHz

1. I think it would be 7.0 to 7.01 MHz, as the AMPLITUDE modulation would not decrease the frequency.

2. 6.99
&7.01

12. direction problem answer is south east

1. No.. North-East

2. yes it's right ans.

3. North -east

4. yes it is north east

5. north east is right

13. I think the op-amp answer is 10 Hz and (Pi)

14. the distance along the semi circle is 5.5 km

1. yes.. 5.5km is the correct answer.. Mine is also that... best of luck

2. yes that is the right answer

15. Least value is e^(~1/e)

1. yes definitely

16. friday 13 th to friday 13 th wont come for the problem .since it is a leap year.

1. 91 days is the answer..

17. i think for diode problem the answer is 8V

1. i think 2 v

2. Apply Kvl:10+i+Vd=0 Ans:2V

18. ratio of triangle area area is 1:3

1. nope its 1:2 u have to do likt this
now you will gate 3/2-1
so its 1/2

2. but i have done by taking formula 1/2*base*height and since height of both triangles are same and base ratio comes out to be 1:3..isnt it correct?

3. Shruti it's 1:2
U can do other way by roughly taking Hieght 3 and then assign/divide base in three equal parts as mentioned in Q uestion.
Calculate area of whole rt. traianglle -subtract area of rt. triange having two/third of the base, ..U wil get area of the trainle .not right angled (as suggested by swaroop) and then compare with area of rt. trianle with base only two times it comes out to be 1:2.
I would say not write comments on answer if U r not 100% confident

4. hmm but u knw u missed out one thing
put this together u will gate

23 December, 2012

5. nope my account is blockd sorry.thats why i hv to dlt ...

It can be done the way Sruthi did also. Find the area using i/2*b*h and subtract one from another. You will get the answer.

19. perturbation problem: ans is 2ab ?

1. yes, it is 2ab.....do you know the answer of the uncertainity in position problem of part B...is it square root of 5 X h divided by square root of 2...

2. yes it was square root 5x/squre root 2

20. length of spring is 10 power 3

1. i got same ans

2. yup same answer for area 1sqr.m, diameter 1mm lenght of wire is 10 power 3

3. Yes. 10^3 is the answer

21. pole and diagonal problem the answer is sq.rt.2a

1. yes definitely

22. coin problem the answer is 1947 . Because in the museum old coins will be kept

1. You really a physics student dear ?? csir made you fool ... the answer will be Year xxx B.C. ... because while printing that coin , none knew that after xxx years , Jesus Christ will born, so it cannot be true... Get it dear ?? All xxx A.D. are correct

2. may be its 200BC

Because after Christ only people started counting year as before and after Christ

4. ha...ha....200 B.C dude

23. triangle problem pythagoras theorem is correct i.e sq.I=sq.II+sq.III

1. correct

2. No
It is I=II+III
becz I,II,III are the area

3. Yes II+III=I is the right answer

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24. what was the answer of partition function problem? any ideas about cutoff for JRf?

1. U have to score at least 75 for ugc and for csir 85 and above

2. JRF 80 MARKS AND FOR LECTURERSHIP 70 MARKKS . THIS DATA IS APPLICABLE FOR GENERAL AND OBC.

3. on which basis u r telling the cut off?? is dre any norm about dat??

4. 45 marks last year cutoff for JRF for general.It may +/-5 this time also.

25. for fermi sphere problm u have to do like that
V=4/3(pi)Ef^3
now Ef=h^2/8m(3n)2/3 where n=N/V
for fcc u have to take 4(multiplication factor) put all this in the volume equation divide by a3 u will get the ans .

26. for LS how much one need to b scored?

1. SEE THE REPLY GIVEN ABOVE FOR SWARUP SANKAR

27. contour problem ans was -16i*pi or +16i*pi...does ans changes when given anticlockwise?

1. I think it is -16i*pi

2. yeah its -19 pi i

3. it is -16*pi*i

4. i mean -16 pi

28. angular momentum problem (ml^2)w/2

29. gate problem y= (a.b)compliment

1. yes 100% correct

30. binary stars root2?

31. 5 marks qs ka answr..b=curla fr one answer..contour integral..i m confused if its anti clockwise then shud it be a minus with b option as answer.. Ebtropy is minimum? d d first qs of part b..is sqrt rawg/rawnoth..is it?

1. anticlockwise contour is +ve
entropy is max. at equilibrium for micro canonical

32. anybody remember that question of peacock and snake moving with same velocity, at what distance peacock will catch snake height 12m n distane of snake from base 36 m...?

33. 25% of 25% is X%, so X is......i think its 6.25 %

1. yes it is corrrect

2. yes, answer will be 6.25%

34. This comment has been removed by the author.

1. yes you are right 12pi/3

36. the answer of uncertainty value of momentum (d)

37. answer of the graph i plotted in mathematica it is cosx/x

1. why not bessel function?

2. it is of bessel fn

3. bassel function.....

4. i think it is (e^-x)*(cos x)

5. yeah ur right

38. yes ans of that coin question may be 200BC

39. what is the answer for the 1.quasi irreversible prcess problem.....2.phase space volume and .......3.the uncertainity in position problem(part b).........plz reply....

40. i dnt think dat LS cut off will b above 62-65. Bcoz d qstn was bit tougher cmprd to d previous ones. Wat do other thinks?

1. This comment has been removed by the author.

2. 45 marks for JRF last year

3. I think this time for JRF 60 to 65 and LS 50 to 55

4. not possible +/-5 may be I m sure

5. we can't guess about the cutoff

6. paper was easy but lengthy so there is a problem of time management

41. finding the missing letter the answer is Z

42. 1-prblem form Bose-Einstien condensate,Chemical potential for 3D isotropic oscillator
Ans:3/2 hcros omega
2-Volueme of fermi sphere
Ans: (12pi^2/a^3)^1/3
3-problem of binary stars, ratio of velocities
Ans: root2
4: Complex function Z^3/(z-2)(z-3)
Ans: -16 pi i
5. 6 spin half partices
Ans: 14 hcross^2
6. perturbation
Ans: 2ba
7. cosx/x plot
8. Limit n-> infinity An+1/An
Ans: 2
9. 91 days in a leap year
10. angular momrntu (ml^2 w)/4
11.

1. http://en.wikipedia.org/wiki/Bose%E2%80%93Einstein_condensate
look this site ...you can see that chemical potential is zero for a BEC

2. In central forces angular momentum is conserved ie,mvr= constant then there is no possibility of root . ans is 2 :for binary stars problem

3. This comment has been removed by the author.

4. ria u r rt

43. anyone from life science ??

44. plz provide life science que ??

1. This comment has been removed by the author.

45. 14x+28y+42z wala que send kro..ans k sath

46. This comment has been removed by the author.

47. phase space trajectories wont intersect each other. Hence ans is the figure with intersected trajectories.(not remembering exact option ,i think b.

1. option was of two circles independent of each other

2. not independent...intersecting each other is wrong one.

48. in part a :which of the distance vs time graph is not possible? it is the one with two distances occuring for same time ...

49. hydrogen atom problem:eigenvalue of Lz was h/8?

1. yes....I have got the same answer

50. part a
in odd city even city problem answer is odd number of odd city is not possible

51. part b
in a 5 series test what is probability of winning toss by saying only heads and winning 3 and lose 2

52. by variational method with H=(-Ñ›^2/2m )d^2/dx^2 -Î±∂(x) find ground state energy with Î¨=Ae^-bx^2

53. what will be the ans of ising model problem?

1. ground state wave function : sech2x

54. This comment has been removed by the author.

1. i think 10, pi

2. This comment has been removed by the author.

55. power across load resistance in solar cell?

56. 1. variation of vector potential inside and outside of solenoid? 2.time average of E square??

57. 1. relativity problem, distance travelled by muons?

58. wht is the value of n im eigen value problem?

1. i think 60

2. This comment has been removed by the author.

59. This comment has been removed by the author.

60. please discuss more on part c physics csir net

61. what is answer of cities?

62. what was ans of lim n-infinity an+1/an?