ISC Physics 2015 Class-12 Solved Previous Year Question Paper for practice. Step by step Solutions of Part I and II with section-A, B, C. Visit official website CISCE for detail information about ISC Class-12 Physics.

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## Previous Year Question Paper ISC Physics 2015 Class-12 Solved

Part – I

Section-A Part – II

Section-B Part – II

Section-C Part – II

### Previous Year Question Paper ISC Physics 2015 Class-12 Solved

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 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)

( ISC Physics 2015 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 :
(i) A short electric dipole (which consists of two point charges, + q and – q) is placed at the center O and inside a large cube (A B C D E F G H) of length L, as shown in figure. The electric flux, emanating through the cube is:

(a) $q / 4 \pi \in_{0} \mathrm{L}$
(b) Zero
(c) $q / 2 \pi \in_{0} \mathrm{L}$
(d) $q / 3 \pi \in_{0} \mathrm{L}$

(ii) The equivalent resistance between points a and f of the network shown in figure is :

(a) 24 Ω
(b) 110 Ω
(c) 140 Ω
(d) 200 Ω

(iii) A moving electron enters a uniform and perpendicular magnetic field. Inside the magnetic field, the electron travels along :
(a) a straight line
(b) a parabola
(c) a circle
(d) a hyperbola

(iv) A fish which is at a depth of 12 cm in water (μ = 4/3) is viewed by an observer on the bank of a lake. Its apparent depth as observed by the observer is :
(a) 3 cm
(b) 9 cm
(c) 12 cm
(d) 16 cm

(v) If Ep and Ek represent potential energy and kinetic energy respectively, of an orbital electron, then, according to Bohr’s theory :
(a) Ek = – Ep/2
(b) Ek = – Ep
(c) Ek= – 2Ep
(d) Ek = 2Ep

B. Answer all questions given below briefly and to the point:
(i) What is meant by the term Quantization of charge ?
(ii) A resistor R is connected to a cell of emf e and internal resistance r. Potential difference across the resistor R is found to be V State the relation between e, V, R and r.
(iii) Three identical cells each of emf 2 V and internal resistance 1 Ω are connected in series to form a battery. The battery is then connected to a parallel combination of two identical resistors, each of resistance 6 Ω. Find the current delivered by the battery.
(iv) State how magnetic susceptibility is different for the three types of magnetic materials, i.e., diamagnetic, paramagnetic and ferromagnetic materials.
(v) An emf of 2 V is induced in a coil when current in it is changed from 0 A to 10 A in 0.40 sec. Find the coefficient of self-inductance of the coil.
(vi) How are electric vector $\overrightarrow{(E)}$, magnetic vector $\overrightarrow{(B)}$ and velocity vector $\overrightarrow{(C)}$ oriented in an electromagnetic wave ?
(vii) State any two methods by which ordinary light can be polarised.
(viii) A monochromatic ray of light falls on a regular prism. What is the relation between angle of incidence and angle of emergence in the case of minimum deviation ?
(ix) What type of lens is used to correct long-sightedness ?
(x) State any one advantage of using a reflecting telescope in place of a refracting telescope.
(xi) State Moseley’s law.
(xii) Wavelengths of the first lines of the Lyman series, Paschen series and Balmer series, in hydrogen spectrum are denoted by  λL,  λP and  λB, respectively. Arrange these wavelengths in increasing order.
(xiii) What is the significance of binding energy per nucleon of a nucleus of a radioactive element ?
(xiv) Write any one balanced equation representing nuclear fission.
(xv) What is the difference between analogue signal and digital signal ?
A.

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

(i) By quantization of charge, we mean that charge is not continuous but exists in discrete magnitude. The minimum charge is e, the charge on the electron. The charge on a body is always an integral multiple of this minimum charge i.e., Q = ± Ne, where N is an integer.
(ii) The required relation is that
$r=\frac{e-\mathrm{V}}{\mathrm{V}} \mathrm{R}$

(iii) The connections are shown in the fig.
Total emf of the cells = 2 + 2 + 2 = 6 V
Internal resistance of the battery =1 + 1 + 1 = 3 Ω
Resistance of the parallel combination $=\frac{6 \times 6}{6+6}=3 \Omega$
Total resistance of the circuit = 3 + 3 = 6 Ω
Current delivered by battery = $\frac{6 \mathrm{V}}{6 \Omega}=1 \mathrm{A}$

(iv) The magnetic susceptibility is :

• – ve for diamagnetic substances.
• + ve but small for paramagnetic substances.
• + ve but large for ferromagnetic substances.

(v) Here, e = 2 V, dl = 10 – 0= 10A, dt=0.4s

(vi) The three are mutually perpendicular as shown :

(vii)

(1) Polarisation by reflection.
(2) By passing unpolarised light through a polaroid.
(viii) In the minimum deviation,
Angle of incidence = Angle of emergence.
(ix) A convex lens of suitable power or focal length.
(x) The image formed by a reflecting telescope is much brighter because there is no loss of light. Further, the image does not suffer from chromatic aberration.
(xi) According to Moseley’s law, the square root of the frequency of characteristic lines in the X-ray spectrum of an element is proportional to the atomic number.
$\text { i.e., } \quad \sqrt{\mathrm{v}} \propto(\mathrm{Z}-\mathrm{b}), \text { where } b \text { is a constant. }$
(xii) The correct order is  λL, λB and λp
(xiii) The stability of a nucleus depends upon the binding energy per nucleon.
(xiv) The desired reaction is
$_{92}^{235} \mathrm{U}+\frac{1}{0} n \longrightarrow_{56}^{141} \mathrm{Ba}+_{35}^{92} \mathrm{Kr}+3_{0}^{1} n+\mathrm{Q}$
where Q is the energy released in the process.
(xv) An analogue signal varies continues with time. They are single valued function of time. Thus, it can have different values. However, a digital signal has two discreet value 0 and 1.0 correspond to a low level and I to a high level. It is shown in fig. ‘a’ and ‘b’

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