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ISC SAMPLE QUESTION PAPER 2015

PHYSICSPAPER – 1(THEORY)(Three hours)

(Candidates are allowed additional 15 minutes for only reading the paper.They must NOT start writing during this time.)

---------------------------------------------------------------------------------------------------------------------Answer all questions in Part I and ten questions from Part II, choosing four questionsfrom Section A, three questions from Section B and three questions from Section C.

All working, including rough work, should be done on the same sheet as, and adjacent to,the rest of the answer.

The intended marks for questions or parts of questions are given in brackets [ ].(Material to be supplied: Log tables including Trigonometric functions)

A list of useful physical constants is given at the end of this paper.---------------------------------------------------------------------------------------------------------------------

PART I (20 Marks)Answer all questions.

Question 1

A. Choose the correct alternative (a), (b), (c) or (d) for each of the questions given below: [5]

(i) Two point charges 17.7 C and -17.7C, separated by a very small distance, are keptinside a large hollow metallic sphere. Electric flux emanating through the sphere is:(a) 2 106 Vm

(b) -2 106 Vm

(c) Zero

(d) 4 106 Vm

(ii) Ohm’s law, in vector form is:(a) J = E

(b) J = E

(c) V = IR

(d) E = J

(iii) If the current (I) flowing through a circular coil, its radius (R) and number of turns (N)in it are each doubled, magnetic flux density at its centre becomes:

(a) Two times

(b) Four times

(c) Eight times

(d) Sixteen times

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ISC SAMPLE QUESTION PAPER 2015

(iv) A person is suffering from the defect of myopia. His far point will be:

(a) Infinity

(b) 25 cm

(c) < 25 cm

(d) About a metre

(v) Ratio of the radius of third Bohr orbit to the radius of second Bohr orbit in hydrogenatom is:

(a) 2:3

(b) 4:9

(c) 9:4

(d) 3:2

B. Answer all questions given below briefly and to the point: [15]

(i) A dielectric slab of relative premittivity (i.e. dielectric constant) 6 isintroduced between the two plates of an 8F air capacitor, in order tocompletely occupy the space between the two plates. Find the newcapacitance of the capacitor.

(ii) Show graphically how resistance of a piece of carbon varies with temperature.

(iii) Current ‘I’ flowing through a metallic wire of area of cross-section ‘a’ isgiven by the equation I = naevd. What is the meaning of the symbols ‘n’ and‘vd’?

(iv) You are provided with four identical cells each of emf 1.5V. How will youconnect all of them to obtain a battery of emf 3V?

(v) What is the value of magnetic field around a current carrying torroid?

(vi) What type of wave front is associated with a line source of light?

(vii) Calculate the polarizing angle for glass whose refractive index is 1.6.

(viii) What is the optical power in dioptre of a concave lens of focal length 50 cm?

(ix) What is meant by resolving power of a telescope?

(x) What is the angle made by a refracted ray with the normal inside aregular (equilateral) prism, in minimum deviation case?

(xi) Name the series of lines in the hydrogen spectrum which lie in the infraredregion.

(xii) What are isotones?

(xiii) Explain the statement: Half-life of polonium is 3.8 days.

(xiv) In a nuclear reactor, what is the function of graphite rods?

(xv) What is amplitude modulation?

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ISC SAMPLE QUESTION PAPER 2015

PART II (50 Marks)

Answer ten questions in this part, choosing four questions

from Section A, three questions from Section B and three questions from Section C.

SECTION AAnswer any four questions.

Question 2

(a) Obtain an expression for intensity of electric field at a point in axial position of an electricdipole.

[3]

(b) Calculate electrostatic potential energy stored in a system consisting of two point charges100µC and 40µC separated by a distance of 9cm, in vacuum.

[2]

Question 3

(a) Two plates of a charged parallel plate capacitor are pulled apart with the help of insulatinghandles, till their separation is doubled.

Compare the new electrostatic potential energy of the capacitor with the old.

[3]

(b) Draw a labelled diagram of a potentiometer circuit used to measure internal resistance of acell.

[2]

Question 4

In Figure 1 below, power developed in resistor R1 is 120W. Find the power developed in resistorR3.

[3]

In a metre bridge experiment to determine unknown resistance of a coil, how is position of thenull point affected if:

[2]

(i) Galvanometer and cell are interchanged?

(ii) Known and unknown resistances are interchanged?

^^^^

^^^^^^^

Figure 1

R2

^^^^30Ω

R3=180Ω

60Ω

R1

I2

I1

I I

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ISC SAMPLE QUESTION PAPER 2015

Question 5

(a) Apply Kirchoff’s Laws to calculate the currents I1 and I2 in the circuit shown in Figure 2below:

[3]

(b) You are given a bar. How will you identify experimentally whether it is made of aferro-magnetic, paramagnetic or a diamagnetic material?

[2]

Question 6

Question 7

(a) Using Ampere’s Circuital Law and with the help of a labelled diagram, show that magneticflux density ‘B’ at a distance r from a long straight conductor is given by:

B = oI

2 r

, where the terms have their usual meaning.

[3]

(b) Define time constant of an RC circuit. What is its SI unit? [2]

(a) (i) In the circuit shown in Figure 3 below, calculate phase difference between thecurrent and the supply voltage:

[4]

(ii) State whether current is leading or lagging behind the supply voltage

(b) What is meant by quality factor of an LCR circuit? [1]

Figure 2

8 Ω3 Ω

4 Ω 4 Ω

3 Ω

FA

B E

8V, 1Ω

16V, 2ΩI1

I2C D

Figure 3

4 F 2H 500Ω

ε = 300 Sin (500t)

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ISC SAMPLE QUESTION PAPER 2015

SECTION BAnswer any three questions

Question 8

Question 10

(a) Prove the law of reflection of light on the basis of Huygens wave theory of light. [4]

(b) Why can’t two independent monochromatic sources of light emitting light of one and thesame wavelength behave as coherent sources?

[1]

Question 9

(a) In Young’s double slit experiment, using light of wavelength 600 nm, 10th bright fringe isobtained on a screen, 3mm from the centre of the pattern. If the screen is 120 cm away fromthe slits, calculate:

[3]

(i) Distance between the two slits;

(ii) Fringe width, i.e. fringe separation.

(b) Show graphically how intensity of light varies in Fraunhofer diffraction. [2]

(a) An optical system consists of a thin convex lens ‘L’ of focal length f = 15 cm and a convexmirror M having radius of curvature R=36 cm, arranged co-axially, at a distance of 24 cm.(See Figure 4 below).

Where should an object O be kept so that its inverted image I formed by the lens mirrorcombination coincides with the object itself?

[3]

(b) A narrow and parallel beam of white light is incident on a convex lens, parallel to itsprincipal axis. Draw a labelled diagram to show how coloured images are formed by thelens.

[2]

O

ML

Figure 4

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ISC SAMPLE QUESTION PAPER 2015

Question 11

(a) Find the distance between the two lenses of a compound microscope if the final imageformed by the microscope is virtual and lies at a distance of 25cm to the left of the eye-piece. Magnifying power of the microscope is 30 and focal lengths of objective andeyepiece are 2cm and 5cm, respectively.

[4]

(b) You are provided with two convex lenses having focal lengths 4cm and 80cm,respectively, to form an astronomical telescope.

Calculate its magnifying power for normal adjustment.

[1]

SECTION C

Answer any three questions.

Question 12

Question 13

(a) Figure 5 below shows a simple diagram of a modern X ray tube. (i.e. Coolidge tube). [3]

(i) Find the minimum wavelength of the X rays emitted by the X ray tube.

(ii) What will be the effect of replacing the 6V battery with a 9V battery on the emittedX rays?

(b) What is meant by mass defect of a nucleus? How is it related to its binding energy? [2]

(a) (i) Explain the statement: “Work function of a certain metal is 2.0 eV.” [3]

(ii) Calculate the maximum wavelength of the electro-magnetic radiation which willcause emission of photoelectrons from this metal.

(b) What is de Broglie hypothesis? What conclusion can be drawn from Davisson andGermer’s experiment?

[2]

6VF

-

66kV

T

Figure 5

mA+

Vacuum

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ISC SAMPLE QUESTION PAPER 2015

Question 14

(a) Starting with the Law of Radioactive Disintegration, show that:

N = Noe-t, where the terms have their usual meaning.

[3]

(b) Calculate the energy released in the following nuclear reaction:

2 2 41 1 2H H He

Mass of 21H = 2.01419u, Mass of 4

2He = 4.00277 u

[2]

Question 15

(a) Draw a labelled circuit diagram of a transistor as a switch and draw its input and outputgraphs.

[3]

(b) What is the symbol of a NOR gate? Write its truth table. [2]

Useful Constants and Relations:

1. Planck’s constant (h) = 6.6 10-34 Js

2. Speed of Light in vacuum (c) = 3.0 108 ms-1

3. Charge of a proton (e) = 1.6 10-19 C

4. Mass of an electron me = 9.1 10-31 kg

5. Permittivity of free space o = 8.85 10-12 Fm-1

6. Constant for Coulomb’s Law0

1

4= 9 x 109 mF-1

7. One electron volt leV = 1.6 10-19 J

8. Unified atomic mass unit lu = 931 MeV

ISC SAMPLE QUESTION PAPER 2015

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SPECIMEN PAPER I OF IIPHYSICS

PAPER – 2

(PRACTICAL)

(Three hours)

(Candidates are allowed additional 15 minutes for only reading the paper.They must NOT start writing during this time.)

----------------------------------------------------------------------------------------------------------------------------ALL ANSWERS MUST BE WRITTEN IN THE ANSWER BOOKLET

PROVIDED SEPARATELY.If squared paper is used, it must be attached to the answer booklet.

Marks are given for a clear record of observations actually made, for their suitabilityand accuracy, and for the use made of them.

Statement of the theory, procedure of the experiment, apparatus, circuit diagrams, precautionsare not required to be written, unless specifically asked for.

Candidates are advised to record their observations as soon as they have been made.All working, including rough work, should be done on the same sheet as, and adjacent to, the rest of

the answer.Mathematical tables and squared paper are provided. The intended marks for questions

or parts of questions are given in brackets [ ].----------------------------------------------------------------------------------------------------------------------------

Answer all questions.You should not spend more than one and a half hours on each question.

Question 1 [12]

This experiment determines the focal length of a convex lens by the displacement method.

(i) Determine the approximate focal length f1 of the given convex lens (marked M) byprojecting the image of a distant object on a wall or a screen. Record the value of f1 incm, correct up to one decimal place.

Figure 1 (a)

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ISC SAMPLE QUESTION PAPER 2015

(ii) Arrange the object pin O, the image pin I and the lens M on an optical bench or table top asshown in Figure 1(a) so that the tips of O and I lie on the principal axis of the lens.

(iii) Adjust the distance x between O and I to be equal to 70 cm. Ensure that this separation ismaintained throughout this particular set up.

(iv) Move the convex lens towards the image pin I and adjust its position until the diminished andinverted image of O coincides with the image pin I.

(v) Read and record the positions of O, M1 and I on the meter scale in cm, correct up to one decimalplace.

(vi) Keeping O and I fixed, move the lens towards the object pin O and adjust its position as shownin Figure 1(b) until the magnified and inverted image of O coincides with I without parallax.Record the new position M2 of the lens.

(vii) The difference between the two positions M1 and M2 of the convex lens is the displacement ‘d’of the lens. Calculate and record the value of d, in cm, correct upto 1 decimal place.

(viii) Repeat the experiment to obtain four more sets of x and d where the range of x is between70 cm and 100 cm.

(ix) Show the image position when the parallax has been removed, in any one of the readingsin (viii) above to the Visiting Examiner.

(x) Tabulate the five sets of values of x, x2, d, d2 and y =2 2

40

x d, along with their units given at

each column head. Compute y up to three significant figures.

(xi) Plot a graph of y against x. Draw the line of best fit and determine its slope S =y

x

= change in

y/change in x.

(xii) Calculate the focal length f of the given lens correct up to one decimal place, using f = 10 S.

(xiii) Record the value of f in the answer book, with proper unit.

Figure 1(b)

ISC Sample Question Papers For Class 12Physics

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