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Einstein Classes, Unit No. 102-103, Vardhman Ring Road Plaza, Vikas Puri Extn., Outer Ring Road,

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EINSTEIN CLASSES

P R E S E N T S

C B S EXIIth Board

PRACTICE ASSIGNMENT

PHYSICS

NOTE THE FOLLOWING POINTS :

1. Einstein Classes is primarily concerned with the preparation ofJEE-ADVANCE /JEE-MAIN/BITS/PMT/AIIMS. We also support the SchoolSyllabus & XIIth Board Preparation in the same program.

2. This assignment is meant to help for those students who are appearing forXIIth CBSE Board Examination.


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SECTION – A

Each question carry 1 mark.

1. Does the mass of the neutral body change after charging and how ?

2. Three equal and positive charges are placed at the corners of an equilateral triangle.Draw the pattern of electric lines of forces.

3. What is the path of the charge particle in the uniform electric field, if it is projectedperpendicular to the field.

4. Draw the pattern of electric lines of forces for infinite non-conducting thin sheet ofpositive charge.

5. A dipole of dipole moment p is placed in the electric field of infinite non-conductingthin sheet of charge of charge density such that the dipole is inclined at a certain angle with the electric field. What is the force, torque and potential energy of the dipole ?

6. Compare equipotential surface and electric lines of forces.

7. Draw the graph for the variation of electric field of spherical charge conductor withdistance.

8. What is the ratio of electric field due to dipole along the axis and along theperpendicular bisector at the large distance ?

9. Why the lines of forces are not closed ?

10. Is the following pattern of lines of forces exists ? Give reasons.

11. What is the mininum electric field at a distance of 1 m from a point charge.

12. Draw equipotential surfaces for an electric dipole.

13. Which of the following quantity is a vector quantity : (i) Current and (ii) Curent density.

14. Draw the variation of resistivity with temperature : (i) for copper (ii) for nichrome(iii) for semiconductor.

15. What is the difference between the potential difference across a battery and emf of thebattery.

16. On which basic principle Kirchhoff’s laws are based ?

17. How the drift speed of the electron will vary if a steady state current will flow through awire of non-uniform cross-section.

18. Why the speed is constant when a charged particle is projected in a magnetic field ?

19. Write down the pairs for the physical quantity which are always perpendicular to each

other for )BV(qF

.


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20. Does the time period to complete one revolution by charge particle in a uniformmagnetic field for circular motion depends on speed ? Give reasons.

21. An electron is moving with constant speed v along a circular path of radius r. Find themagnetic field at the center ?

22. A wire of given length is folded into a circular loop of several turns N. Find thedependence of magnetic field at the centre on N ?

23. Draw the variation of magnetic field due to current carrying loop along the axis.

24. What is the ratio of magnetic field due to solenoid inside and at the end point ?

25. What is the magnetic dipole moment due to circulating electron of charge e in an orbit ofradius r ? Compare this with the orbital angular momentum of the electron. The speed ofthe electron is v.

26. What is the gauss law in magnetism ?

27. Why the soft iron core is used for electromanget, whereas steel for permanent magnet ?

28. Which substance has the behaviour independent of temperature and why ?

29. On which basic principle the Lenz law is based ?

30. Write down the unit and dimension of inductance.

31. What is the physical meaning of quality factor ?

32. Arrange the following in the increasing order of the wavelength :

Radiowave, X-rays, UV-rays, -rays.

33. Write down the different conditions for good contrast interference pattern ?

34. If Young’s double slit experiment is shifted from air to water then what changes willoccur ?

35. Why the focal length of the lens changes when the wavelength of the light used changed.

36. Why the sky is blue ?

37. Draw the variation of kinetic energy of electron in photoelectric effect with frequency ofincident light.

38. Why the wave theory of light is not able to explain photoelectric effect ?

39. Compare the wavelength associated with electron with kinetic energy 1eV andwavelength associated with photon of the same energy.

40. How the radius of the Bohr orbit depends on quantum number n.

41. Write down the properties of nuiclear force ?

42. Compare the radius of the nucleus of hydrogen and oxygen.

43. Which particles are emitted in –decay and in + decay.

44. Draw the I-V characteristics for a photo diod and solar cell.

45. What is the frequency band for satellite communication ?


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46. An alpha particle is moving vertically downwards in a magnetic field in N-S direction.In which direction will the alpha particle be deflected.

47. Magnetic lines prefer to pass through iron than air, why ?

48. What is the rate of work done by a magnetic field on a charge ?

49. In the fig.

What should be magnitude and direction of electric field so that charge goesundeviated ?

50. Why can’t tranformer be used to step up d.c. voltage ?

51. What is the power factor of an LCR series circuit at resonance ?

52. What is the focal length and power of the lens in the figure. The radii of curvature of thetwo faces are R each.

53. A small piece of stone is dropped into a still water reservoir. What is the shape of wavefront formed ?

54. What should be the order of size of obstacle or aperature for the light to diffract.

55. A ray of light falls on a transparent slab of µ = 3. If reflected and refracted rays aremutually perpendicular, find out the angle of incidence ?

56. A polariser and an analyzer are so oriented that no light is transmitted. The analyzer isthen rotated through 600. What fraction of the maximum light is transmitted ?

57. Law of energy conservation is obeyed in interference pattern. Justify.

58. Give an equation representing the decay of a free neutron.

59. Why are de-Broglie waves associates with a moving football not visible ?

60. Why is the penetrating power of gamma rays very large ?

61. Which have greater ionising power : alpha particles or beta particles ?

62. The thickness of base in a transistor is increased. How will the collector current beaffected ?


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63. In a p-n junction what is the direction of diffusion current ?

64. A p-n photodiode is fabricated form a semiconductor with back gap of 2.8eV. Can itdetect a wavelength of 6000nm ?

65. For the given direction of E and B fields in an em wave, how can one find the directionof proparation of the wave ?

66. Which type of em waves are used for telecommunication purpose through artificialsatellites ?

67. What is ground wave propagation ?

68. What is sky wave propagation ?

SECTION – B

Each question carry 2 marks.

1. Calculate the Coulomb force between a proton and an electron separated by0.8 × 10–15 m and compare with the gravitational force between them. Also calculate theCoulomb force between two -particles separated by a distance 3.2 × 10–15 m.

2. Define capacitance and its units. Derive an expression for the capacitance ofparallel plate capacitor.

3. In a parallel plate capacitor, the capacitance increase from 4 microfarad to 80microfarad, on introducing a dielectric medium between the plates. What is thedielectric constant of the medium ?

4. The capacitor is disconnected from the charging battery, explain how the

(i) capacitance,

(ii) p.d. across the plates, and

(iii) energy stored

in the parallel plate capacitor change, when a medium of dielectric constant ‘k’ isintroduced between the plates.

5. An electric dipole of dipole moment p is placed along the direction of the uniformexternal electric field ‘E’. It is disturbed from this position by very small angle. Explainwhat happens to the dipole on being released.

6. Two point electric charges of unknown magnitude and sign are placed a distance ‘d’apart. The electric field intensity is zero at a point, not between the charges but on theline joining them. Write two essential conditions for this to happen.

7. An -particle and a proton are accelerated through the same potential difference.Calculate the ratio of velocities acquired by the two particles.

8. Two point changes +4µC and –6µC are separated by a distance of 20 cm in air. At whatpoint on the line joining the two charges is the electric potential zero ?


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9. A proton, placed in a uniform electric field of magnitude 2 × 103 NC–1, moves from apoint A to B in the direction of electric field. If AB = 0.05m, calculate the

(i) potential difference between A and B, and

(ii) work done in moving the proton from A to B.

10. An electric flux of –6 × 103 Nm2/C passed normally through a spherical Gaussiansurface of radius 10 cm, due to a point charge placed at the centre.

(i) What is the charge enclosed by the Gaussian surface ?

(ii) If the radius of the Gaussian surface is doubled, how much flux would passthrough the surface ?

11. A metal wire is bent in the shape of a circle of radius 10 cm. It is given a charge of 20µC,which is spread uniformly over it. Calculate electrical potential at the centre of the circle.

12. A 10µF capacitor can withstand a maximum voltage of 100 volts across it whereasanother 20µF capacitor can withstand a maximum voltage of only 25 volts. What is themaximum voltage that can be put across their series combination ?

13. A dry cell of e.m.f. 1.6 V and internal resistance 0.10 ohm is connected to a resistor ofresistance R ohm. If the current drawn from the cell is 2A

(i) what is the voltage drop across R ?

(ii) what is the energy dissipation in the resistor ?

14. Write two special characteristics of magnanin due to which it is used in making standardresistances.

15. A carbon resistor of 74 k is to be marked with rings of different colours for itsidentification. Write the sequence of colours.

16. The current through a wire depends on time as I = io + At where i

o = 5A and A = 2As–1.

Find the charge crossing through a section of the wire in 15 seconds.

17. Establish the relation between drift velocity Vd of the electrons in a conductor of cross

section ‘A’ carrying current ‘I’ and concentration of free electrons per unit volume of theconductor being ‘n’.

18. Explain the phenomenon of hysterisis in magnetic materials.

19. Derive the expression for the torque on a recrangle lar coil of area A, carrying a currentI placed in a magnetic field B. The angle between the direction of B and the vectorperpendicular to the plane of the coil is .

20. Give the position of a magnetic dipole held in a magnetic field, where its potentialenergy is (i) minimum (ii) maximum. Also draw the graph for the variation of potentialenergy with the angle between the magnetic dipole and the field.

21. How does the intensity of magnetisation of a paramagnetic material vary with increas-ing applied magnetic field ?

22. State and illustrate Curie law in magnetism.


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23. An electron of kinetic energy 25 keV moves perpendicular to the direction of a uniformmagnetic field of 0.2 millitesla. Calculate the time period of rotation of the electron inthe magnetic field.

24. Give any two factors by which current senstivity of a galvanometry can be increased.

25. Cyclotron is not suitable for accelerating electrons, why ?

26. A proton, deutron and an alpha particle with equal K.E’s, enter the same magnetic fieldB perpendicular to it, compare radii of their circular paths.

27. What happens to (i) Pole strength (ii) Magnetic moment. If a bar magnet is cut into twoequal pieces (i) transverse to its length (ii) along its length.

28. Find the equivalent magnetic moment.

29. A straight long conductor is carrying current of 5A in east to west direction. Findmagnitude and direction of B at point 4cm away northward.

30. Prove that the smallest magnetic moment available with an atom is (eh/4m).

31. Define the term ‘self-induction’. Write two factors which the self-inductance of a coildepends.

32. A coil A is connected to a voltmeter V and the other coil B to an alternating currentsource D. If a large copper sheet C, is placed between the two coils, how does the in-duced e.m.f. in the coil A change due to current in coil B ?

33. Calculate the current drawn by the primary of a transformer, which steps down 200 V to20 V to operate a derive of resistance 20 . Assume the efficiency of the transformer tobe 80%.

34. A rectangular coil of N turns and area of cross-section A, is held in a time-varyingmagnetic field given by B sin t, with the plane of the coil normal to the magnetic field.Deduce an expression for the e.m.f. induced in the coil.

35. An air-core solenoid is connected to an a.c. source and a bulb. If an iron-core is insertedin the solenoid, how does the brightness of the bulb change ? Give reason for youranswer.

36. A choke coil and a bulb are connected in series to an a.c. source. The bulb shines brightly.How does its brightness change when an iron core is inserted in the choke coil ?

37. Give the direction of induced current (if any) in the metal ring when the magnet ismoved away form the rig as shown.


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38. Why do we prefer carbon brushes than copper in an a.c. generator ?

39. v-I graph for two series LCR circuit A and B is shown below. Which of the two has largervalue of resistance.

40. Why do we prefer a choke coil in place of a resistor in any safety devise ?

41. Give the direction of induced current (if any) in metal rings I and II.

42. Explain how will the brightness of bulb be affected if (I) frequency of ac is increased (II)a resistor is put in series.

43. A capacitor blocks d.c., favours a.c. why ?

44. What is the role of transformers in long distance transmission of electrical power.Illustrate your answer with an example.

45. In the adjoining figure magnetic field is of strength Band rectangular loop of length l andbreadth w. Show graphically

46. Explain briefly the formation of mirage in deserts.

47. Define phase difference and relate this with the path difference.

48. Find the ratio of intensities at two points x and y on a screen in Young’s double slitexperiment, where waves from S

1 and S

2 have path difference of (i) 0 and (ii) /4.

49. For the same angle of incidence, the angles of refraction in three different media A, Band C are 150, 250 and 350 respectively. In which medium will the velocity of light beminimum ?

50. Give two difference between interference and diffraction pattern of light.

51. Calculate the refractive index of the material of an equilateral prism for which the angleof minimum deviation is 600.


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52. You are given two convex lenses of focal length 80 mm and 800 mm. Which one willyou use as an objective and which one as an eyepiece for constructing an astronomicaltelescope ?

53. The two slits in Young’s double sit experiment are separated by a distance of 0.03 mm.An interference pattern is produced on a screen 1.5 m away. The 4th bright fringe is at adistance of 1 cm from the central maximum. Calculate the wavelength of light used.

54. How can one distinguish between an unpolarized light beam and a linearly polarizedlight beam using a polaroid ?

55. Sketch the wave-fronts corresponding to converging rays.

56. Draw a ray diagram to show the formation of the image of an object placed between fand 2f of a thin concave lens. Deduce relation between the object distance, the imagedistance and the focal length of the lens under this condition.

57. Define lateral displacement. On what factor does it depend ?

58. Complete it with correct value of angle of emergence.

59. A fish is situated at the depth ‘h’ inside a lake. Calculate the radius of circular aperturethrough which the fish seen the out wide world.

60. A reflecting telescope has a large mirror for its objective with radius of curvature equalto 80 cm. What is the magnifying power of the telescope if the eyepiece used has a focallength of 1.6 cm ?

61. Distinguish between Nuclear fission and fusion.

62. Why is the energy distribution of beta rays continuous ?

63. Name the reaction which takes place when a slow neutron beam strikes U23692 nuclei.

Write the nuclear reaction involved.

64. The frequency (v) of incident radiation is greater than threshold frequency (v0) in a

photocell. How will the stoping potential vary if frequency (v) is increased, keepingother factors constant ?

65. A source of light is placed at a distance of 50 cm from a photocell and the cut-offpotential is found to be V

0. If the distance between the light source and photocell is made

25 cm what will be the new cut-off potential ? Justify your answer.

66. State with reason why light nuclei usually undergo nuclear fusion.


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67. Radiations of frequency 1015 Hz are incident on two photosensitive surfaces P and Q.Following observations are made :

(i) Surface P : Photoemission occurs but the photoelctrons have zero kinetic energy,and

(ii) Surface Q : Photoemission occurs and photoelectrons have some kinetic energy.

Which of these has a higher work function ? If the incident frequency is slightly reduced,what will happen to photoelectron emission in the two cases.

68. How is the depletion region formed in a p-injuction diode ?

69. The output of a 2-input NOR gate is fed to a NOT gate. Write down the truth table for theoutput of the combination for all inputs.

70. Draw the energy band diagram of a p-type semiconductor. How does the forbidden en-ergy gap of an intrinsic semiconductor vary with increase in temperature ?

71. What do you mean by rectification ? With the help of a circuit diagram, explain the useof p-n junction diode as a full wave rectifier and half wave rectifier, giving its input andoutput waveforms.

72. If A = 0, B = 0. Find y for the given combination of tages.

73. Diodes D1 and D

2 are ideal diodes. Find the current drawn form the battery of emf 5V if

the positive terminal is connected to

(i) the point A

(ii) the point B

74. If the input frequency is 50Hz. What is the output frequency of

(i) Half wave rectifier

(ii) Full wave rectifier

75. What role does ionosphere play in communication ?

76. Why is short wave communication over long distance not possible via ground waves ?

77. A certain plane em wave emitted by an antenna has a wavelength of 3.0 cm and amaximum amplitude of the electric field of 3 × 102 Vcm–1.

(a) What is the frequency of the wave ?

(b) What is the magnitude of the maximum magnetic field ?


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78. The coverage range of a TV tower is 60 km. Calculate the height of the tower. Takeradius of earth to be 6400 km.

79. Why do we need Modulation (Give two reasons)

SECTION – C


1. Derive an expression for the energy stored in a parallel plate capacitor with air as t h emedium between its plates. How does the total energy stored by the capacitor changewhen the medium of air is replaced by a medium of dielectric constant K ? Explain.

Show that electric field E itself is a source of energy with energy density .JmE2

1 320

2. Capacitors P, Q and R have each a capacity C. A battery can charge the capacitor P to apotential difference V. If after charging P, the battery is disconnected from it and thecharged capacitor P is connected in following separate instances to Q and R (i) to Q inparallel, and (ii) to R in series, then what will be the potential difference between theplates of P in the two instances ?

3. State Gauss’s theorem in electrostatics. Apply this to calculate the field intensity (i) atany point inside and outside a hollow and solid charged conducting sphere. (ii) at anypoint inside and outside of the solid non-conducting charged sphere also draw thevariation of electric field with distance.

4. You are given an isolated parallel plate capacitor of capacitance C charged to a potentialdifference V. What will happen to the following when the separation between the platesis doubled with the help of insulating handles attahced to the plates ?

(a) charge on the plates

(b) potential difference across the plates

(c) field between the plates

(d) energy stored in the capacitor

5. Two point electric charges of values q and 2q are keep at a distance d apart from eachother in air. A third charge Q is to be kept along the same line in such a way that the netforce acting on q and 2q is zero. Calculate the position of charge Q in terms of q and d.

6. Calculate the potential and field at the centre of a square of side 2 m, which carries atits four corners charges of +2 nC, + 1nC, –2 nC and –3 nC respectively. Also calculatethe work done to carry a charge particle of +10nC from infinity to the center of thesquare.

7. A parallel plate capacitor has capacitance of 30pF. What will its capacitance become inthe two cases shown below when it is half-filled with a dielectric of dielectric constant ?


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8. Find the equivalent capacitance of the following network between A and B.

9. Explain the principle of potentiometer, with the help of a circuit diagram, explain how apotentiometer can be used to compare e.m.f. of two primary cells.

10. Find the value of unknown resistance X in the following circuit for which current flowsthrough section AO is zero. Also calculate the current drawn by the circuit from thebattery of e.m.f. 6V and negligible internal resistance.

11. Explain, by drawing a labelled diagram, how a positively charged particle is acceleratedin a cyclotron.

12. Distinghish between dia, para and ferro magnetic substances. Give one example of each.How does the magnetic property of iron change with increase of temperature ?

13. A beam of electrons passes undeflected through mutually perpendicular electric andmagnetic fields E and B respectively. If the electric field is cut-off, the electron beammoves in a circular path of radius ‘r’. Derive the expression for e/m of electrons in termsof r, E and B.

14. A magnet oscillating in a horizontal plane, has a time period of 3 seconds at a placewhere the angle of dip is 300 and 4 seconds at another place, where the dip is 600.Compare the resultant magnetic field at the two places.

15. An electron and a proton moving with the same speed enter the same magnetic fieldregion at right angles to the direction of the field. For which of the two particles will theradius of circular path be smaller ? Compare the time period to complete one revolution.

16. State Amperes circuital law. Derive expression for magnetic field due to solenoid at apoint inside it.


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17. A domain in ferromagnetic iron is in the form of a cube of side of length 1 µm. Estimatenumber of iron atoms in the domain and maximum possible dipole moment. Themolecular mass of iron is 55g/mole and its density is 7.9g/m3. Assume that each ironatom has a dipole moment of 9.57 × 10–24 Am2.

18. A short magnet placed with its axis at 300 experiences a torque of 0.16 N.m in anexternal field of 800G. (a) What is the magnetic moment of magnet. (b) What is the workdone by an external torque in turning it from stable equilibrium to unstable equilibrium.

19. (a) What are eddy currents ?

(b) How are eddy currents produced ? Give two application of eddy currents.

20. Draw the graphs to show the variation of (i) XL, and (ii) X

C with the frequency of the a.c.

source used.

A 200 V variable frequency a.c. source is connected to a series combination of L = 5 H,C = 80 µF and R = 40 . Calculate (i) angular frequency of the source to get maximumcurrent in the circuit, (ii) the current amplitude at resonance and (iii) the powerdissipation in the circuit.

21. Twelve wires of equal lengths are connected in the form of a skeleton-cube which is

moving with a velocity v

in the direction of a magnetic field B

. Find the emf in eacharm of the cube.

22. Prove that an ideal inductor does not dissipate power in an a.c. circuit. A bulb ofresistance 10, connected to an inductor of inductance L, is in series with an a.c. source

marked 100 V, 50 Hz. If the phase angle between the voltage and current is 4

radian,

calculate the value of L.

23. A circular copper disc 10 cm in radius rotates at 20 rad/s about an axis through itscentre and perpendicular to the disc. A uniform magnetic field of 0.2 T acts perpendicu-lar to the disc.

(i) Calculate the potential difference developed between the axis of the disc and therim.

(ii) What is the induced current, if the resistance of the disc is 2 ohm ?

24. Define the term root-mean-square (rms) value of a.c. Derive the relation between rmsand peak value of a.c. A 1 µF capacitor is connected to a 220 V, 50 Hz a.c., source.Calculate the rms value of the current through the circuit. Also find the peak value ofvoltage across the capacitor.

25. How does the mutual inductance of a pair of coils change when;

(i) the distance between the coils is increased ?

(ii) the number of turns in each coil is decreased ? Justify your answer in each case.

26. Prove that total energy stored in an inductor is ½LI2max

, where Imax

is the maximumcurrent through the inductor. In which form is this energy store.

27. Define resolving power of a telescope & microscope and give the expression for itsresolving power.


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28. What do you understand by polarisation of light ? How can the transverse nature of lightbe demonstrated experimentally ?

29. Deduce lens maker’s formula for a thin biconves lens.

30. Derive the expression for the fringe width in Young’s double slit interferenceexperiment.

31. A double concave lens made of glass of refractive index 1.5 has both radii of curvatureof magnitude 40 cm. An object 2 cm high is placed at 10 cm from the lens. Find theposition, nature and size of the image.

32. The image of an object formed by a lens on the screen is not in sharp focus. Suggest amethod to get clear focusing of the image on the screen without disturbing the positionof the object, the lens or the screen.

33. What are coherent source of light ? Why is no interence pattern observed when twocoherent sources are

(i) infinitely close to each other ?

(ii) far apart from each other ?

34. A slit of width ‘d’ is illuminated by light of wavelength 6,500 Å. For what values of ‘d’will the

(i) first minimum fall at an angle of diffraction of 300 ?

(ii) first maximum fall at an angle of diffraction of 300 ?

35. In the hypothetical fission reaction :

92X236

aY141 +

36Zb + 3

0n1

What are the values of the numbers a and b ? Calculate the total energy released pernuclear fission in MeV units when the masses in amu units are

of neutron = 1.009

of X-nucleus = 235.891

of Y-nucleus = 140.673

of Z-nucleus = 91.791

36. How does (i) photoelectric current, and (ii) kinetic energy of the photoelectrons emittedin a photocell vary if the intensity of the incident radiation is doubled ? When light ofwavelength 400 nm is incident on the cathode of a photocell, the stopping potentialrecorded is 6 V. If the wavelength of the incident light is increases to 600 nm, calculatethe new stopping potential.

37. In an experiment of photoelectric effect, the graph between the maximum Kinericenergy (E

k) of the emitted photoelectron and the frequency v of the incident light is

straight line shown in the fig. Calculate (a) Threshold frequency (b) Work function ofcathode metal in electron volt (c) Planck’s constant h and (d) Maximum K.E. ofelectrons emitted by light of frequency v = 30 × 1014 s–1.


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38. What is a n-p-n transistor ? How dies it differ from p-n-p transistor ? Give their sysmbols.Explain transistor action.

39. Draw the logic symbol and truth table for a NAND gate, AND gate, OR gate, NOR gateand Ex-OR gate.

40. In a transistor, the base current is changed by 20 µA. This result in a change of 0.02 V inbase to emitter voltage and a change of 2 mA in the collector current. (a) Find (i) thecurrent gains ‘

ac’ and (ii) transconductance ‘g

m’. (b) If this transistor is used as an

amplifier with the load resistance 5 k, calculate the voltage gain of the amplifier.

41. What is a zener diode ? How is it symbolically represented ? With the help of a circuitdiagram, explain the use of zener diode as a voltage stabilizer.

42. A semiconductor has equal electron and hole concentration of 4 × 108 / m3. On dopingwith a certain impurity, hole concentration increases to 8 × 1012 / m3 :

(i) Identify the new semiconductor obtained after doping,

(ii) Calculate the new electron concentration and

(iii) How does the energy gap vary with doping ?

43. Explain how a transistor works as a Switch ?

44. Two signals A and B as shown in figure are used as two input of (i) AND gate (ii) NORgate (iii) NAND gate (iv) OR gate. Obtain the output in each of the four cases.

45. What is meant by the term ‘modulation’ ? Explain with the help of a block diagram, howthe process of modulation is carried out in radio broadcasts.

46. What is 'amplitude modulation' and 'frequency modulation' ? Show these processgraphically.

47. Explain with the help of input and output waveforms, how a diode can be used fordetection of AM waves ?


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SECTION – D


1. (a) Define electric dipole moment. Derive an expression for the electric field andpotential at any point along the (i) equatorial line (ii) axial line of an electricdipole. Show mathematically that the electric field intensity due to a short dipoleat a distance ‘d’ along its axis is twice the intensity at the same distance along theequatorial axis.

(b) Derive an expression for the total work done in rotating the dipole through anangle ‘’ in uniform electric field ‘E’. Also derive the torque acting on thedipole.

2. Explain the construction, basic principle and working of a Van de Graff generator withthe help of a diagram.

3. What are the Kirchoff’s laws for electric circuit. Apply Kirchoff’s laws to obtain thecondition of balance in a Wheatstone’s bridge.

4. State Biot-Savart’s law. Using Biot-Savart’s law, derive the expression for magneticfield due (i) to current circular coil, at a point along the axis of the coil (ii) infinite wire.

5. (a) Derive the relation for the force per unit length between two infinity longparallel straight wires carrying currents. Hence define one ampere.

(b) Explain why two straight parallel metallic wire carrying current in oppositedirections repel each other.

6. (a) Explain with the help of a labelled diagram, the underlying principle,construction and working of a moving coil galvanometer.

(b) Define voltage sensitivity and figure of merit of a moving coil galvanometer.Give its S.I. unit.

7. Derive an expression for the impendance of a LCR series AC circuit. A 40 resistor,3 mH inductor and 2µF capacitor are connected in series to a 110 V, 50 Hz AC source.Calculate the value of the current in the circuit.

8. Draw a labelled diagram of an a.c. generator. Write the principle on which it works.

An a.c. generator consists of a coil of 100 turns and cross-sectional area of 3 m2, rotatingat a constant angular speed of 60 radian/sec in a uniform magnetic field of 0.04 T. Theresistance of the coil is 500 ohm. Calculate (i) maximum current drawn from thegenerator and (ii) maximum power dissipation in the coil.

9. Explain the terms reactance and impedance as applied to components of an a.c. circuit.A variable frequency 230 V alternating voltage source is connected across a seriescombination L = 5.0 H, C = 80 µF and R = 40 Calculate

(i) the angular frequency of the source which drives the circuit in resonance,

(ii) the amplitude of the current at resonating frequency and

(iii) rms potential drop across the inductor at resonating frequency.


New Delhi – 110 018. Ph. : 9312629035 (17)

10. When an alternating voltage of 200 V is applied across a device Z, a current of 0.5 Aflows through the circuit and is in phase with the applied voltage. When the samevoltage is applied across another device Y, the same current again flows through thecircuit but it leads the applied voltage by /2 radians.

(a) name the devices X and Y.

(b) Calculate the current flowing in the circuit when same voltage is applied acrossthe series combination of X and Y.

11. Explain, with the help of a diagram, the principle, construction and working of a step-uptransformer. Why is its conlaminated.

12. (a) Draw a labelled diagram of a compound microscope and explain its working.

(b) With the help of ray diagram, illustrate the formation of the final image of anobject in a compound microscope. Derive an expression for its magnifying power.How can the magnifying power be increased ?

(c) How will the resolving power of compound microscope be affected when (a) thefrequency of light used to illuminate the object is increased, and (b) the focallength of the objective is increased. Justify your answer in each case.

13. (a) State Huygen’s Wave theory and its assumptions ? Also define coherent sourceof light

(b) Deduce (i) laws of reflection (ii) laws of refraction on the basis of Huygen’sprinciple.

14. (a) Draw a labelled diagram of an astronomical telescope forming the final image atthe near point. Write down the formula for its magnifying power.

(b) What is the effect of increasing the diameter of the objective of a telescope on its

(i) magnifying power and

(ii) resolving power ?

(c) Draw a labelled ray diagram for a refracting type astronomical telescope. Howwill its magnifying power be affected on increasing for its eye-piece (i) the focallength, and (ii) the aperture ? Justify your answer.

15. (a) A slit of width ‘a’ is illuminated by monochromatic light at normal incidence.Draw the intensity distribution curve observed on the screen, due to diffraction.

(b) Determine the angular separation between central maximum and first ordermaximum of the diffraction pattern due to a single slit of width 0.25 mm. whenlight of wavelength 5890 Å is incident on it normally.

(c) In a single slit diffraction pattern, how is the angular width of central brightmaximum changed, when

(i) the slit width is decreased

(ii) the distance between the slit and the screen is increased


New Delhi – 110 018. Ph. : 9312629035 (18)

16. Define interference of light. Two sources of equal amplitude are used to produceinterference. Drive an expression for the variation of intensity with phase angle. Henceplot a graph to show this variation. Also derive an expression for the variation ofintensity with phase angle for unequal amplitude.

17. Draw a ray diagram to show the formula of real images of a point object due to convexspherical refracting surface, when the ray of light is travelling from rarer medium ofRefractive index (µ

1), to denser media of Refractive Index (µ

2).

Using the diagram derive a relation between object distance (u) and image distance (v)radius of curvature ‘R’ of a convex spherical surface. State the sign conventions and theassumptions made.

18. Draw the graph to show variation of binding energy per nucleon with mass number ofdifferent nuclei.

Calculate binding energy per nucleon of Ca4020 nucleus.

19. Explain what is mean by radioactive decay. A radioactive nucleus is represented by the

symbol Vab . How is the new nucleus represented after the emission of (i) an alpha

particle, (ii) a beta particle and (iii) a gamma ray ? The activity of a source undergoing asingle type of decay is I

0 at time t = 0. Obtain an expression in terms of the half-life T

½

for the activity I at any subsequent time t.

20. Draw the experimental arrangement used by Davison and Germer for electron diffrac-tion by crystals. In this experiment what is the maximum accelerating potential appliedto the electron to get maximum scattering angle of 500 from the nickel crystal. Usingthese data verify the wave nature of electron.

21. Explain through a labelled circuit diagram, the working of a transistor as an amplifier(common emitter configuration). Obtain an expression for the voltage gain.

22. What do the following terms stand for ?

(a) FAX (b) MOD EM (c) PCM

(d) LED (e) LASER (f) AM

(g) FM

C B S E - einstein classeseinsteinclasses.com/P_Assgn.pdf · C B S E XIIth Board ... JEE-ADVANCE...

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