ISC Physics 2014 Class-12 Solved Previous Year Question Paper for practice. Step by step Solutions of Part I and II with section-A, and B. Visit official website CISCE for detail information about ISC Class-12 Physics.

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## Previous Year Question Paper ISC Physics 2014 Class-12 Solved

Part – I

Section-A Part – II

Section-B Part – II

Maximum Marks: 70
Time allowed: 3 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 questions from Section A, three questions from Section B.
• 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)

( ISC Physics 2014 Class-12 Solved Previous Year Question Paper )

Question 1.
(A) Choose the correct alternative (a), (b), (c) or (d) for each of the questions given below : [5]
(i) The intensity of electric field at a point at a perpendicular distance ‘r’ from an infinite line charge, having linear charge density ‘λ’ is given by:
(a) $E=\left(\frac{1}{4 \pi \epsilon_{0}}\right) \frac{\lambda}{r}$
(b) $E=\left(\frac{1}{4 \pi \epsilon_{0}}\right) \frac{2 \lambda}{r}$
(c) $E=\left(\frac{1}{4 \pi \epsilon_{0}}\right) \frac{\lambda}{r^{2}}$
(d) $E=\left(\frac{1}{4 \pi \epsilon_{0}}\right) \frac{2 \lambda}{r^{2}}$

(ii) If R1 and R2 are filament resistances of a 200 W and a 100 W bulb respectively, designed to operate on the same voltage, then:
(a) R1 = R2
(b) R2 = 2R1
(c) R2 = 4R1
(d) R1 = 4R2

(iii) A metallic wire having length of 2 m and weight of 4 x 10-3 N is found to remain at rest in a uniform and transverse magnetic field of 2 x 10-4 T. Current flowing through the wire is:
(a) 10 A
(b) 5 A
(c) 2 A
(d) l A

(iv) When a beam of white light is passed through sodium vapors and then through a spectrometer, spectrum so obtained has two dark lines present in the yellow region. This spectrum is called:
(a) band spectrum
(b) continuous spectrum
(c) absorption spectrum of sodium
(d) emission spectrum of sodium

(v) If l3 and l2 represent angular momenta of an orbiting electron in III and II Bohr orbits respectively, then l3: l2 is :
(a) 3:2
(b) 9:4
(c) 2:3
(d) 4:9

(B) Answer all questions given below briefly and to the point: [15]
(i) A parallel plate air capacitor has a capacitance of 5 μF. It becomes 50 μF when a dielectric medium occupies the entire space between its two plates. What is the dielectric constant of the medium ?

(ii) Find the emf of the battery shown in figure :

(iii) Two substances A and B have their relative permeability slightly greater and slightly less than 1 respectively. What do you conclude about A and B as far as their magnetic materials are concerned?

(iv) When does a moving charged particle nor experience any force while moving through a uniform magnetic field ?

(v) What is the turns ratio i.e., transformer ratio, ns: np, in an ideal transformer which in-creases ac voltage from 220 V to 33000 V ?

(vi) What is meant by coherent sources of light ?

(vii) A ray of light is incident on a transparent medium at polarizing angle. What is the angle between the reflected ray and the refracted ray ?

(viii) Name the physical principle on which the working of optical fibers is based.

(ix) What is meant by shortsightedness ?

(x) How does focal length of a convex lens change with increase in wavelength of incident light?

(xi) With reference to photoelectric effect, what is meant by threshold wavelength ?

(xii) Half life of a certain radioactive element is 3.465 days. Find its disintegration constant.

(xiii) Binding energy per nucleon for helium nucleus (2 He) is 7.0 MeV Find value of mass defect for helium nucleus.

(xiv) Write one balanced reaction representing nuclear fusion.

(xv) Draw the truth table of a NOR gate.
(A)

(i) (b)
(ii) (b)
(iii) (a)
(iv) (c)
(v) (a)

(B) \begin{aligned} \text { (i) We know that } &=\mathrm{KC}_{0} \\ \therefore \mathrm{K} &=\frac{\mathrm{C}}{\mathrm{C}_{0}}=\frac{50}{5}=10 \end{aligned}

(ii) Net emf of the cells in each row = 6 V
Since the two rows are connected in parallel.
Net emf = emf of each row = 6 V

(iii) Since the permeability of a paramagnetic is slightly greater than 1 and that of a diamag¬netic substance is less than A, A must be paramagnetic and B must be diamagnetic.

(iv) Charged particle does not experience any force when it moves in the direction of the magnetic field.

(v) $\frac{n_{s}}{n_{p}}=\frac{E_{s}}{E_{p}}=\frac{33000}{220}=150$

(vi) Two sources of light which emit light of the same frequency and wavelength having a constant phase difference between them and preferably of the same amplitude are called coherent sources. They are desired from the same source.

(vii) When the ray of light is incident at the polarizing angle, the angle between the reflected and refracted ray is 90°.

(viii) Optical fibers are based on the principle of total internal reflection.

(ix) It is a defect of the eye. A shortsighted person can see only near objects clearly but is not able to see far objects clearly. It is due to the decrease in focal length of the eye lens.

(x) The focal length of a convex lens increases as the wavelength increases. This is so because the refractive index decreases with increase in wavelength of light.

(xi) Threshold wavelength is the maximum wavelength of light corresponding to which the photoelectric effect just starts.

(xii) TH = 3.465 days, λ = ?

(xv) The truth table for NOR gate which is a combination of ‘OR’ gate followed by a NOT gate is given below

Section-A Part – II (20 Marks)

(a) An electric dipole of dipole moment $\vec{p}$ is placed in a uniform electric field $\vec{E}$ with its axis inclined to the field. Write an expression for the torque $\vec{T}$ experienced by the dipole in vector form. Show diagrammatically how the dipole should be kept in the electric field so that the torque acting on it is: