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GATE 2012, Question Paper, Download, Answer key, pdf file 12 february - Comment the description of Answers

►GATE 2012, Question Paper, Download, Answer key, pdf file 12 february - Comment the description of Answers

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GATE 2012 Question Paper Clik Here to Download


GATE2012 Official Published AnswerKey -  Paper:Physics
1 (A)  2 (C)  3 (A)  4 (C)  5. Marks to All 6 (A)  7 (B)  8 (D)  9 (C)  10 (A)
11 (A)  12 (C)  13 (D)  14 (B)  15. Marks to All 16 (C)  17 (B)  18 (B)  19 (D)  20 (A)
21 (D)  22 (B)  23 (D)  24 (D)  25 (C)  26 (A)  27 (C)  28 (A)  29 (B)  30 (C)
31 (D)  32 (A)  33 (B)  34 (A)  35 (D)  36 (C)  37 (A)  38 (C)  39 (B)  40 (D)
41 (B)  42 (B)  43 (C)  44 (D)  45 (D)  46 (B)  47 (A)  48 (C)  49 (D)  50 (A)
51 (A)  52 (C)  53 (B)  54 (B)  55 (B)  56 (D)  57 (A)  58 (B)  59 (A)
60 Marks to All 61 (C)  62 (B)  63 (B)  64 (D)  65 (A)

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70 comments:

  1. Here are my answers
    QS. - 1 Ans B (Linearly dependent)
    2 - C
    3 - B
    4 - C
    5 - C
    6 - A
    7 - A Not Sure
    8 - D
    9 - C
    10 - B
    11 - C
    12 - C
    13 - D Not Sure
    14 - B Not Sure
    15 - B
    16 - A
    17 - B
    18 - B
    19 - D Not Sure
    20 - A
    21 - D not sure
    22 - A not sure
    23 - A
    24 - D
    25 - B not sure

    ReplyDelete
  2. 26 - B Not Sure
    27 - C
    28 - A
    29 - B
    30 - C
    31 - B
    32 - A Not Sure
    33 - B
    34 - D
    35 - C
    36 - A Not Sure
    37 - A
    38 - C
    39 - B
    40 - D
    41 - C Not Sure
    42 - B
    43 - A Not Sure
    44 - D Not Sure
    45 - D
    46 - A Not Sure
    47 - A
    48 - A Not Sure
    49 - C Not Sure
    50 - D Not Sure
    51 - C Not Sure
    52 - C
    53 - A
    54 - B
    55 - B
    56 - A Not Sure
    57 - A
    58 - B
    59 - A
    60 - B
    61 - C
    62 - B
    63 - B
    64 - D Not Sure
    65 A

    ReplyDelete
  3. mention the Set Code guys . I means these answers are for Set A, B, C or D.

    ReplyDelete
  4. @vbk5mnnit
    CORRECTION TO THE ABOVE ANSWERS
    5-D
    11-A
    13-A
    14-B
    16-C
    21-D
    22-A
    25-C
    26-A
    31-D
    32-A
    35-B
    36-C
    46-D
    47-D
    48-C
    49-C
    50-A

    ReplyDelete
  5. regarding the vectors a and b
    i think they are linearly independent
    bcoz u cannot write one in terms of other
    So the answer should be (A)

    ReplyDelete
  6. 1 B 21 A 31 D 41 D 51 A 61 C
    2 C 22 C 32 A 42 A 52 C 62 B
    3 B 23 A 33 A 43 B 53 A 63 B
    4 C 24 B 34 D 44 D 54 B 64 D
    5 D 25 B 35 C 45 B 55 B 65 A
    6 A 26 C 36 A 46 C 56 A
    7 A 27 B 37 C 47 A 57 A
    8 D 28 B 38 A 48 C 58 B
    9 C 29 D 39 B 49 B 59 A
    10 D 30 A 40 C 50 D 60 B
    please check these key for gate 2012 physics these are correct

    by; Mohit Sharma
    iit kharagpur

    ReplyDelete
  7. please check these answer for gate 2012 physics
    by; MOhit Sharma IIT Kharagpur

    1 B
    2 C
    3 B
    4 C
    5 D
    6 A
    7 A
    8 D
    9 C
    10 D

    21 A
    22 C
    23 A
    24 B
    25 B
    26 C
    27 B
    28 B
    29 D
    30 A

    31 D
    32 A
    33 A
    34 D
    35 C
    36 A
    37 C
    38 A
    39 B
    40 C

    41 D
    42 A
    43 B
    44 D
    45 B
    46 C
    47 A
    48 C
    49 B
    50 D

    51 A
    52 C
    53 A
    54 B
    55 B
    56 A
    57 A
    58 B
    59 A
    60 B

    61 C
    62 B
    63 B
    64 D
    65 A

    ReplyDelete
  8. @ mohit sharma
    dear cross check your some of the answers
    like for 30-will be C others
    30-c,33-b,35-d,38-c and some others like for 37,40,42 and some others

    ReplyDelete
  9. @MOHIT SHARMA IIT@KGP

    do you have solutions for questions 11-20??

    ReplyDelete
  10. Try to explain the answer and not just simply putting the answer.

    Again can someone explain why a and b were linearly dependent.

    ReplyDelete
    Replies
    1. Anonymous24 May, 2012

      i agree with your comment

      Delete
  11. @MOHIT SHARMA IIT@KGP.. mention the set for which you have given the answers

    ReplyDelete
  12. I think raj is right.. Should be independent..
    1} A

    ReplyDelete
  13. can i get the answer for 26

    ReplyDelete
  14. 1 have answer is A correct. i have solution it is linearly independent. have anyone of solution 5 1nd 24 question correctly

    ReplyDelete
  15. dear sharma, check your ans. i thought there are more wrong

    ReplyDelete
  16. correction
    Answer 1. (A)
    Two vectors u and v are linearly independent if the only numbers x and y satisfying xu+yv=0 are x=y=0. If we let and there
    dterment should not be zero.

    ReplyDelete
  17. Vbk5nnit answers are more reliable..

    ReplyDelete
  18. 1-A
    because a1k1+a2k2=0 and a1=0 also.
    4-C
    Id.c=2Ipeak/3.14
    5-A
    E=h2(nx2+ny2)/8ma2.here nx=ny=1
    we get than A is correct.
    8-D
    9-A
    12-C
    resistivity=1/ne*mobility.
    14-B
    15-B
    19-D
    B=del cross A
    E=-grad phhi- delA/del T
    20-A
    23-C
    24-C
    E=(n+1/2hw). here n=0 for ground state
    25-C
    independent component=n(n+1)/2. here n=3
    26-A
    28-A
    29-B
    30-C
    33-B
    35-C
    40-B
    42-B
    43-B
    44-A
    48-C
    E=-crossH/2m(d2/dx2shai
    49-A
    54-A
    55-D
    60-A
    63-B
    65-A

    ReplyDelete
  19. plz chk my result and tell if you get somthing wrong after searching book.

    ReplyDelete
  20. Any guess about this years cut off marks????

    ReplyDelete
  21. @arpan please explain how B is correct for question 40..

    ReplyDelete
  22. @raj
    yes u are right . they are independent..

    ReplyDelete
  23. Answers with my explanations(verified from relevant books)

    *************************************************************
    1) As already said a and b should be linearly independent
    Answer = A
    *************************************************************
    2) the MI of rod when the axis passing through the centre and perp to the rod is given by:

    I=(M*l^2)/12

    In our case M = M1+M2 and l = 2L so I = (M1+M2)(2L)^2/12 = (M1+M2)L^2/3
    Answer = C
    *************************************************************
    3) This is striaght forward the time average of the cos function gives the 1/2 factor

    Answer = B
    *************************************************************
    6) Check wiki
    http://en.wikipedia.org/wiki/Compressibility

    Answer = A
    **************************************************************
    7) The formula comes out to be
    DeltaE = g *mu * B
    where DeltaE = difference in energy , g = landeg factor ,mu=bohr magneton , B=applied mag field

    So all we have to do is find the g factor for the given state of sodium Na

    Now g = 1 + (j(j+1) + s(s+1) - l(l+1)) / 2 j(j+1)

    when u put l=0(bcoz given state is s) , s=1/2(bcoz 2s+1=2) and j = 1/2

    we get g = 1 + 1 = 2

    Answer = 2*mu*B = B

    ******************************************************************

    8)The fermi energy is given by the formula

    Ef = some constant * n^(2/3)

    also Ef = 1/2 * m * vf^2 were vf = fermi velocity

    from the above two relation we get that fermi velocity = vf = some constant * n^(1/3)


    Answer = D

    *****************************************************************************

    9) this can found by elimination method

    proton = baryon = bound state of three quarks
    =not a fundamental particle bcoz its made from quarks = A) and B) are wrong
    meson = bound staet of quark-antiquark
    = not a fundamental particle bcoz its made from quarks = D) is wrong

    Answer = C
    *******************************************************************************
    14) http://en.wikipedia.org/wiki/Orbital_eccentricity

    Answeer = B

    ********************************************************************************
    10)For GM counter B) is wrong bcoz particle type cannot be identified
    C) is wrong bcoz info of energy is lost
    D) is wrong bcoz oprating vol is definetly not in few volts its around 300 volts or so


    Answer = A

    **************************************************************************************


    16) The energy difference for raman rot spectra is given by = B(4J+6) were B=rotational constant

    first stoke/anti-stoke line appear at 6B from the centre and the rest are seprated by 4B

    S0 12.96 = 6B
    B = 2.16

    Answer = C
    *****************************************************************************************

    18) the given spatial part of wavefunction is symmetric so the spin part has to be anti-symmetric


    answer = B

    ******************************************************************************************
    19) use B= del cross A and E = -Del phi - dA/dt

    answer = D

    ******************************************************************************************
    20) A

    21) either C or D not 100% sure

    25) symmetric component = n(n+1)/2 = 3(3+1)/2 = 6

    answer = C
    ********************************************************************************************
    Do reply if u find any mistake.

    ReplyDelete
  24. @ Mr Sharma, there are some wrong answer in ur soln. 29-B, since the sum of eigen values is equal to the sum of principal diagonal.

    ReplyDelete
  25. I think answer for 24 is D.
    In the truncated harmonic potential only even numbers are permissible for n.(Because hermite polynolial should vanish at x=0). ie, E=(2n+1+1/2).

    ReplyDelete
  26. @Raj Nair

    in question no 7, they have asked for the difference in the energy of levels from the original one in the presence of magnetic field. so it should be muB*B no. the difference between the splitted energy levels between will be 2*muB*B. am i right?

    ReplyDelete
  27. @Arpan kumar nayak iitkgp
    arpan please check again (40-D) we both checked this with text book and please check this reference once again (http://hyperphysics.phy-astr.gsu.edu/hbase/hydwf.html#c1) and (44-D) because if we expend e^1/z the we get series 1+1/z+.... then we can solve it by normal method and we will get 2*pie*i so answer is D.

    ReplyDelete
  28. @Raj,

    I've a doubt your ans qn no 3.

    They asked to find time averaged energy density associated with electric field.

    Energy density = 1/2*(epsilon)*E^2

    Here E=E0 Cos(wt-kz)

    ie, Energy density =1/2*(epsilon)*E0^2*Cos^2(wt-kz)

    On taking time average,
    Energy density=1/4(epsilon)E0^2.

    then (A)'ll be the answer.

    (I think so,may be wrong)

    ReplyDelete
  29. friends any guesses about this year cutt off marks..

    ReplyDelete
  30. 50-A
    group velocity is derivative of \omega. so first derivative will give cos. but first brillouin zone boundary condition make it as cos(90). so answer is zero.

    ReplyDelete
  31. @Physics Lover

    Actually the time average of cos^2 gives 1/2 factor.

    This is nicely explained in griffiths ch 9 pg 381.look at the footnote of that page.

    or check the link below for the screenshot of that page.

    http://imageshack.us/photo/my-images/638/83949441.png/

    ReplyDelete
  32. @Neethal

    yes u r right

    DeltaE = 2*bohr magneton * B

    So answer is option B

    ReplyDelete
  33. @MOHIT SHARMA IIT@KGP

    I agree with u on 44-D

    as already explained
    The residue of exp(1/z) at 0 is by definition the coefficient of
    1/z in the Laurent expansion of exp(1/z) about 0. We have
    exp(1/z) = 1 + 1/z + (1/z)^2/2! + ...,
    so the residue is 1.

    So answer is 2*pi*i*residue = 2*pi*i

    ReplyDelete
  34. @Anonymous

    yes u r right.

    frist derivative gives cos(k*a/2)
    also for first BZ k=pi/a
    S0 v=cos(pi/2)=0

    Answer 50)A

    ReplyDelete
  35. @MOHIT SHARMA IIT@KGP

    also 40)D is right.

    the radial pbb density will have a mixima.

    ReplyDelete
  36. Saurabh Sahu & Bindesh Shukla says

    1- A
    2- C
    3- B
    4- C
    5-
    6- A
    8- D
    9- C
    11- D
    13- B
    14- B
    17- B
    18- B
    19- D
    23- B
    25- B
    27- C
    29- B
    30- C
    34- D
    35- D
    39- B
    40- D
    42- B
    43- A
    47- A
    49- D
    50- D
    54- A
    55- A
    56- A
    57- A
    58- B
    59- A
    60- A
    61- C
    62- A
    63- B
    65- A

    ReplyDelete
  37. @Arpan kumar nayak iitkgp
    sir plz correct the answer of q.54
    ans54=b

    ReplyDelete
  38. @Raj Nair
    in q.25 independent components are asked. so plz check ur ans.are independent and symmetric components are same???

    ReplyDelete
  39. @Physics Lover
    agree with u that answer of q.24=d

    ReplyDelete
  40. sir how it is b?if we take b option for Q.54,then we will get wrong answer for Lagrangian equation.pls justify ur answer

    ReplyDelete
  41. @raj nair, abt no. 3

    I've seen that.
    But that is the energy density for electric and magnetic field combined.They are asking about the energy density associated with electric field only. In an EM wave electric and magnetic field contributes 1/4*(epsilon)*E^2 each and final energy density'll be 1/2*(epsilon)*E^2.



    And answer for 40 can never be D.
    If you put r/a=0 in the given equation for P(r) is not zero.The answer is C i think.

    ReplyDelete
  42. @Physics Lover

    The answer for 40) is D becoz the the radial pbb density is proportional to r^2 times mod psi square.

    so the function looks like this
    y=x^2 exp(-2x)
    If u plot this function u fill find a maxima.
    actually the peak in the graph corresponds to bohr radius a0

    Check out the links below to confirm

    http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/hydr.html

    http://www.physicsforums.com/showthread.php?t=49807

    ReplyDelete
  43. @Physics Lover

    Regarding the energy density store in EM fields

    for electric field it is (1/2)epsilon E^2
    for magnetic field it is (1/2)B^2/mu

    thats why the total is written as u=1/2(epsilon E^2+B^2/mo)

    Even if we assume what u r saying is correct then how do get the factor 1/4

    ReplyDelete
  44. For q)34 why answer is D)

    i think it should be A)

    any explanations

    I think D) is wrong bcoz quarks do interact through weak interactions.

    From wiki "A quark of one flavor can transform into a quark of another flavor only through the weak interaction, one of the four fundamental interactions in particle physics......."

    ReplyDelete
  45. @Raj Nair

    Yes for electric field it is 1/2*epsilon*E^2.

    What is E here?

    E=E0 Cos(wt-kz)

    Substitute and take time average.

    that'll add an additional 1/2 to the eqution.

    ReplyDelete
  46. @Raj Nair

    But i think in the hyperphysics link,the graph is not similar to ours for it plots the derivative of probability density.

    The probability density is P(r)=1/(4*Pi*a^3)exp[-2r/a0]

    when r/a0=0,

    P(r)=1/4*Pi*a0^3 which is nonzero.

    In the option D, P(r)=0 for r/a0=0

    Also I can't understand how this can be approximated to function of the form x^2 exp[-2x] when a0 is a constant,not variable here.

    Can you pls explain these?

    ReplyDelete
  47. Can anybody tell me the answers for 20,33 and 43 with explanation?

    ReplyDelete
  48. @Physics Lover

    If u look in griffiths ch 9 eq 9.55

    it says that u = epsilon E^2

    and that the electric and magnetic contributions are equal

    im not sure now but i think vector E is to be substitued in equation 9.55 which is epsilon E^2

    ReplyDelete
  49. @Physics Lover

    first have a look at this link

    http://www.physicsforums.com/showthread.php?t=49807

    Actually P(r) = r^2*Exp[-r] where i have not included the constants

    but the point is that we do have a variable r^2(coming from the volume element) multiplied by the exponential so the function goes to zero as r goes to zero.

    So the answer is D)

    ReplyDelete
  50. @Physics Lover
    For 20) answr is A)

    becoz the voltage at the inverting terminal is +1V becoz of the voltage divider connected.

    so as soon as the voltage at the non-inverting terminal(vin) goes above +1V the output will go into positive saturation(+10V)

    So this happens only in option A)

    ReplyDelete
  51. correct answers
    1-b
    2-c
    3-a
    4-c (2*10/pi)
    5-d

    6-a
    7-b
    8-d
    9-c (elementary particles, all other not)
    10-doubt

    11-a (use reflectivity equation with n=3/2)
    12-c (conductivity 0.288, take invesrse)
    13-a (for 2D kinetic energy Kb T, but here K.E=1/2 mv^2=1/2 m(Vx^2+Vy^2). Since they asked mean (1/2) of velocity square answer is a
    13-a
    14-b
    15-b

    16-c (first raman line 6B)
    17-b
    18-b
    19-d
    20-doubt

    21-d (properties of nuclear force)
    22-a
    23-
    24-
    25-c

    26-a
    27-
    28-a
    29-b
    30-c

    31-d
    32-a
    33-c
    34-d
    35-b

    36-c
    37-(a or c)
    38-c
    39-b
    40-d

    41-
    42-b
    43-
    44-d
    45-d
    46-
    47-a

    48-c (free space-V=0)
    49-d (for real part wave function and its conjugate are same)
    50-a

    51-b (square \omega and integrate both side from -pi/a to +pi/a)
    52-
    53-
    54-b
    55-b

    56-
    57
    58-b
    59-q
    60-b

    61-
    62-b
    63-b
    64-
    65-a

    ReplyDelete
  52. DINESH IIT BOMBAY20 February, 2012

    for linearly indepdent vectors p*vector a +q*vector b =0 where p and q should be zero explicitly.so answer A is correct for question 1.

    ReplyDelete
  53. DINESH IIT BOMBAY20 February, 2012

    HERE 1/2 FACTOR WE ARE GETTING FROM ENERGY DENSITY FORMULA AND WE HAVE TO GET AVERAGE SO 1/2 FACTOR WILL COME OUT FROM AVERAGE OF COSINE SQUARED.

    ReplyDelete
  54. can anyone explain me the question (62) an automobile plant ........

    ReplyDelete
  55. in question no. 62,
    suppose total 100 shock obsorbers company has to buy.then 60 will be supplied by X and 40 by Y.
    (.40*72)/100=.288
    (.60*96)/100 =.576
    then probabilty is .288/(.577+.288) =.334
    so, ans is B

    ReplyDelete
  56. plz explain the answer to q. no. 38

    ReplyDelete
  57. ans to Q.38 is C because
    Z = ge^-β€
    acc. to Question
    Z = 1 + 2e^(-β€) + e^(-2β€)
    where g is the degeneracy factor,
    can u plz explain me ans to q. 35 and 36

    ReplyDelete
  58. @Anonymous but according to the question of probability the question ask us to calculate the probability of finding the reliable shock absorber which are made by Y from all (i.e. we have to include the probability of getting non reliable also) so the answer is 0.288

    ReplyDelete
  59. U r right.
    But .288 represents the shock obsorbers which are reliable. so probability is number of reliable shock obsorbers divide by the total number of reliable cases.

    I think so........

    ReplyDelete
  60. @Anonymous my friend I would like to correct you...... the question nowhere ask us to pick the shock absorber from the reliable one.... it ask us to pick the shock absorber randomly.... so there is probability of getting non reliable shock absorber also...

    ReplyDelete
  61. Read the end line of question 62.
    THE probability that a randomly chosen shock obsorber,which is found to be reliable, is made by Y is.....

    ReplyDelete
  62. @MOHIT SHARMA IIT@KGP
    its(40) a standard ques wid standard fig...nd 1 basic thing prob f electron in nucleus shud b zero

    ReplyDelete
  63. hello .. any idea abt dis years cutoff for ph??

    ReplyDelete
  64. how acc. To ur own explanatin answr of q 38 is corect.its d instead c.

    ReplyDelete
  65. @Anonymous

    explanation of q. no. 38 is-------


    you know the partion function given by-:
    Z=sigma*g*exp(-beta*E(energy))
    here g is called degeneracy.

    and sigma run from 1 to 3 bcoz three energy levels are given i.e
    0, e , 2e.so

    Z=1*exp(-beta*0)+2exp(-beta*e)+1*exp(-beta*2e)
    here 2 is multiplied in second term bcoz in question says that the energy level 'e' are two fold degenerated i.e the degeneracy g=2.

    so- Z=1+2exp(-beta*e)+exp(-beta*2e)

    so- Z=(1+exp(-beta*e))^2

    so answer is-- 38-C.

    ReplyDelete
  66. @DINESH IIT BOMBAY

    my dear Dinesh--

    Ans. 3-B

    please see the below notes of chapter-9 of quantum mechanics by David j Grifith.

    ReplyDelete
  67. @Anonymous

    explanation of q.no.-35 is---

    both move in same direction so first find relative velocity i.e-
    (2c/3)-(c/2)
    c/6
    then put this velocity c/6 in length conraction formula you get
    ans. 35-D

    ReplyDelete
  68. hiii, arpan. your ans of question 24 is wrong.it wil b (D).As it is unsymmetrical .ground state energy wl b 3/2 hcros omega.so first e.state wl 7/2 hcros omega

    ReplyDelete

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