Comment the Detailed answers of the questions below. Do not comment the answers you are not sure.

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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**Comment only the correct answers**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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Here are my answers

ReplyDeleteQS. - 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

26 - B Not Sure

ReplyDelete27 - 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

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

ReplyDelete@vbk5mnnit

ReplyDeleteCORRECTION 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

regarding the vectors a and b

ReplyDeletei think they are linearly independent

bcoz u cannot write one in terms of other

So the answer should be (A)

1 B 21 A 31 D 41 D 51 A 61 C

ReplyDelete2 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

please check these answer for gate 2012 physics

ReplyDeleteby; 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

@ mohit sharma

ReplyDeletedear 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

@MOHIT SHARMA IIT@KGP

ReplyDeletedo you have solutions for questions 11-20??

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

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

i agree with your comment

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

ReplyDeleteI think raj is right.. Should be independent..

ReplyDelete1} A

can i get the answer for 26

ReplyDelete1 have answer is A correct. i have solution it is linearly independent. have anyone of solution 5 1nd 24 question correctly

ReplyDeletedear sharma, check your ans. i thought there are more wrong

ReplyDeletecorrection

ReplyDeleteAnswer 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.

Vbk5nnit answers are more reliable..

ReplyDelete1-A

ReplyDeletebecause 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

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

ReplyDeleteAny guess about this years cut off marks????

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

ReplyDelete@raj

ReplyDeleteyes u are right . they are independent..

Answers with my explanations(verified from relevant books)

ReplyDelete*************************************************************

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.

@ 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.

ReplyDeleteI think answer for 24 is D.

ReplyDeleteIn 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).

@Raj Nair

ReplyDeletein 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?

@Arpan kumar nayak iitkgp

ReplyDeletearpan 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.

@Raj,

ReplyDeleteI'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)

friends any guesses about this year cutt off marks..

ReplyDelete50-A

ReplyDeletegroup 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.

@Physics Lover

ReplyDeleteActually 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/

@Neethal

ReplyDeleteyes u r right

DeltaE = 2*bohr magneton * B

So answer is option B

@MOHIT SHARMA IIT@KGP

ReplyDeleteI 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

@Anonymous

ReplyDeleteyes 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

@MOHIT SHARMA IIT@KGP

ReplyDeletealso 40)D is right.

the radial pbb density will have a mixima.

@Physics Lover

ReplyDeleteit is right

Saurabh Sahu & Bindesh Shukla says

ReplyDelete1- 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

@Arpan kumar nayak iitkgp

ReplyDeletesir plz correct the answer of q.54

ans54=b

@Raj Nair

ReplyDeletein q.25 independent components are asked. so plz check ur ans.are independent and symmetric components are same???

@Physics Lover

ReplyDeleteagree with u that answer of q.24=d

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@raj nair, abt no. 3

ReplyDeleteI'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.

@Physics Lover

ReplyDeleteThe 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

@Physics Lover

ReplyDeleteRegarding 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

For q)34 why answer is D)

ReplyDeletei 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......."

@Raj Nair

ReplyDeleteYes 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.

@Raj Nair

ReplyDeleteBut 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?

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

ReplyDelete@Physics Lover

ReplyDeleteIf 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

@Physics Lover

ReplyDeletefirst 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)

@Physics Lover

ReplyDeleteFor 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)

correct answers

ReplyDelete1-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

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.

ReplyDeleteHERE 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.

ReplyDeletecan anyone explain me the question (62) an automobile plant ........

ReplyDeletein question no. 62,

ReplyDeletesuppose 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

plz explain the answer to q. no. 38

ReplyDeleteans to Q.38 is C because

ReplyDeleteZ = 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

@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

ReplyDeleteU r right.

ReplyDeleteBut .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........

@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...

ReplyDeleteRead the end line of question 62.

ReplyDeleteTHE probability that a randomly chosen shock obsorber,which is found to be reliable, is made by Y is.....

@MOHIT SHARMA IIT@KGP

ReplyDeleteits(40) a standard ques wid standard fig...nd 1 basic thing prob f electron in nucleus shud b zero

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

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

ReplyDelete@Anonymous

ReplyDeleteexplanation 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.

@DINESH IIT BOMBAY

ReplyDeletemy dear Dinesh--

Ans. 3-B

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

@Anonymous

ReplyDeleteexplanation 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

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