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12th PUBLIC PHYSICS - KEY ANSWERS - MARCH-2018 PART-I Q.NO

Q.NO

A-TYPE

B-TYPE

b a d d c c

uncontrolled fission reaction in a direction bisecting angle ACB Scanning α-paricles zero an ON switch

1 2 3 4 5 6

d a a a a a

intensity of incident radiation 10.7 MHz immobile positive ions capacitor 0.66 milli coulomb

7 8 9

a d a

7 8 9

b c a

contracts conservation of energy in a direction bisecting angle ACB

10 11 12 13

a c b b

0.66 milli coulomb intensity of incident radiation diffraction pattern becomes narrower and crowded together the velocity of the particle neither a net force nor a torque 0,0

10 11 12 13

b a c a

uncontrolled fission reaction 59 26Fe -27 10 kgms-1

14 15 16 17 18 19 20

a d b d d b/c c

10.7 MHz 1 Transverse E-1 absorbs green light m2V-1s-1 or Cskg-1 conservation of energy

14 15 16 17 18 19 20

b/c c b d c a b

21 22

a b

capacitor phenomenon of conversion of kinetic energy into radiation

21 22

d a

23

a

23

d

m2V-1s-1 or Cskg-1 neither a net force nor a torque 0,0 1 an ON switch high specific resistance phenomenon of conversion of kinetic energy into radiation 9 minutes diffraction pattern becomes narrower and crowded together absorbs green light

24 25

c a

10-27 kgms-1

24 25

d b

E-1

26 27 28 29 30

a a a b d

immobile positive ions 59 26Fe high specific resistance contracts 9 minutes

26 27 28 29 30

c a d b d

zero the velocity of the particle scanning transverse α-paricles

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1 2 3 4 5 6

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1

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Important Note: 1. For answers in Part – II , Part-III, and Part- IV like reasoning , explanation, narration,description and listing the points, students may write in their own words but without changing the concepts and without skipping any point. 2. Answers written only in BLACK or BLUE should be evaluated. 3. For graphical representation, X and Y variables must be mentioned . If not , reduce ½ mark. 4. Marks should be given to the unit, only if the answer is correct for problems.

PART-II Q.No

37

om .c

ar

w

38

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35 36

Mere equation F = Polar molecule – correct definition Any one example Electrical resistivity – correct definition Unit = Ohm meter Rt = Ro(1+αt) Substitution Rt = 14 Ω (correct answer +unit) Emf and potential difference ( any two 2x1½) Ampere’s circuital law – correct statement (or) = µo Io e = -Blv substitution e =-0.0164 V (correct answer +unit) Q – factor – correct statement (or) Q= (or) Q =

si

34

3

.a

33

Coulomb’s law - Correct statement

w

32

MARK TOTAL

w

31

Description

39 40

41 42

43 44 45

3

1 2 1 2 1 1 1 ½ +½ 3 3 1 1 1 ½ +½ 3

3 3 3

3 3

3

3

1

Huygen’s principle – correct statement (2x1½) rn = (or) λ = substitution λ = 5400 Ȧ (correct answer +unit) Correct conditions – Achieve laser action 2d sin = nλ substitution λ max = 5.64 x 10 -10 m(correct answer +unit) Any 3 uses of Electron microscope (3x1) Any 3 properties of β – rays

3 1 1 ½ +½

3 3

3 1 1 ½ +½ 3 3

3 3

Correct definition - Pair production Annihilation of matter

1½ 1½

3

3 3

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46 47 48

Proper simplification using Boolean Algebra Any 3 advantages of negative feedback (3 x 1=3) De Morgan’s theorems (2 x 1½) (OR) Mere equations (1+1) Proper circuit diagram – OR gate using diodes Any 3 advantages of digital communication

49 50

3 3 3

3 3 3

2 3 3

3 3

PART-III Electric lines of forces : Any 5 properties of electric lines of forces (5x1)

52

Daniel cell Diagram Construction Working Mentioning – cannot supply steady current for long time Emf = 1.08 V Superconductors : Any 5 applications of Superconductors (5x1)

5

ar

substitution and calculation B= 9.9x 10-5 T (correct answer +unit) Mutual Induction of two long Solenoid Diagram Explanation Upto ɸ2=MI1 upto M = Radius of nth Dark ring in Newton’s Experiment: Diagram Explanation

w

w

56

.a

si

55

B=

riy

52 54

.c

om

57

w

Upto 2t = Condition for darkness 2t = nλ rn = Spectral series of Hydrogen atom Explanation of five series Formula (or) Mere mentioning the names of spectral series only Einstein’s photo electric equation: Quantum theory – mentioning Interaction between photon and single electron of a metal surface Explanation - Utilization of energy of photon in two ways hʋ = W + ½ mv2 if the electron does not lose energy by internal collisions the entire energy ( hʋ- w ) will be exhibited as kinetic energy of the electron

57

58

1 1 2 ½ 1/2 5 2 2 ½+½

5

5 5

5 1 1 2 1 5 1 1 1 1 1 5 2½ 2½ 2 5 ½ 1 1 1 ½ B.KANNAN M.Sc., B.Ed.,

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59

hʋ = W + ½ mvmax2 (or) h(ʋ-ʋo) = ½ mvmax2 Problem

1 5 2

l = lo

(OR)

om

61

substitution t = 5.022 days (correct answer +unit ) b. reactant mass = 4.4 MeV Product mass = 28 MeV Mass defect E = 23.6 MeV α and β relation: Current gain in CB Mode α =

2 1 1 1 2 1

.c

60

substitution v = 0.423 x 108 ms-1 (correct answer +unit) Compulsory Problem a.N = Noe-λt λ=

Current gain in CE Mode β =

riy

Radar Principle Any 4 applications of radar (4x1)

Electricfield – Axial line Electric dipole definition Diagram Explanation E1 = (along BP)

w

w

63

E2 =

1½ 1½ 1 1 1

5

1 1 2 5 1 4

PART - IV

w

.a

62

(or) α =

si

upto β =

ar

α=

5

(along PA)

10 1 1 1 1 1 1

E = E1 + (-E2 ) 2 Upto E =

64

(along BP)

P =q x 2d E acts in the direction dipolemoment

1 1

Force acting on a current carrying conductor placed in a magnetic field: Diagram

2

4 10

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=m =

68

w

.a

L=

=

w

Upto

w

67

si

riy

ar

.c

66

2 1 1 1 1 1 1 10 2 1 2

om

65

Explanation I = nAeVd Il = - nAevd f = -e (vd x B) F = Nf F = - nAlevd x B F = Il x B AC Generator – single phase Diagram Principle Explanation of 4 parts – (4x1/2 ) (mere mentioning the parts – 1 mark Direction of induced current given by Flemming Right Hand rule First half cycle Second half cycle e = Eo sinωt ; Eo= NBAω Output sine wave form Types of Spectra Definition of Emission spectrum Explanation of continuous spectrum Explanation of line spectrum Explanation of band spectrum Definition of absorption spectrum Explanation of continuous absorption spectrum Explanation of line absorption spectrum Explanation of band absorption spectrum (OR) Mentionin the kind of Emission and Absorption spectrum(1+1) Radius of nth orbit in Bohr atom model Postulates (2x1) Explanation

1 1 1 1 1 10 2 1 1 1 2 1 1 1 10 2 1 2 1 1

Upto arriving the following relation

1

rn = for hydrogen atom Z = 1

1

rn =

1

BainBridge Mass Spectrometer Diagram Accurate determination of atomic masses Description Eq = BqV (or) V = Explanation of effect of magnetic field B’ in the chamber B’qV = mv2 / r

2 1 2 1 1

10

1 B.KANNAN M.Sc., B.Ed.,

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69

1+1 10 1 2 1 1 1 1 1 1+1 10 4 1 2 1 1 1

ar

.c

om

70

m = and Measurement of R Bridge rectifier Definition for rectification Circuit diagram Construction Explanation of positive half cycle Explanation of negative half cycle Current flows through RL in the direction, during both half cycles of input a.c signal Efficiency 81.2% Input and output waveforms Superheterodyne AM receiver Correct block diagram Explanation R.F Amplifier Mixer and local oscillator IF amplifier Detector AF amplifier

riy

PREPARED BY

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B.KANNAN M.Sc., B.Ed., BT ASST IN ( SCIENCE ) GHSS, MUDUR-631 003 VELLORE DT

B.KANNAN M.Sc., B.Ed., www.tnmanavan.blogspot.com