ISC Physics 2018 Class-12 Previous Year Question Papers

ISC Physics 2018 Class-12 Solved Previous Year Question Paper for practice. Step by step Solutions with Questions of section-A, B, C and D. Visit official website  CISCE for detail information about ISC Class-12 Physics.

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ISC Physics 2018 Class-12 Solved Previous Year Question Paper 

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Maximum Marks: 70
Time allowed: Three hours

  • Candidates are allowed additional 15 minutes for only reading the paper. They must NOT start writing during this time.
  • All questions are Compulsory.
  • This question paper is divided into 4 sections, A, B, C and D as follows
  • Section A: Question number 1 is of twelve marks. All parts of this question are compulsory.
  • Section B: Question numbers 2 to 12 carry 2 marks each with two questions having internal choice.
  • Section C: Question numbers 13 to 19 carry 3 marks each with two questions having internal choice.
  • Section D: Question numbers 20 to 22 are long-answer type questions and carry 5 marks each.
  • Each question has an internal choice.
  • The intended marks for questions are given in brackets [ ].
  • All working, including rough work, should be done on the same sheet as and
  • adjacent to the rest of the answer.
  • Answers to sub parts of the same question must be given in one place only.
  • A list of useful physical constants is given at the end of this paper.
  • A simple scientific calculator without a programmable memory may be used for calculations.

Section – A

Answer all questions.

ISC Physics 2018 Class-12 Previous Year Question Papers Solved

Question 1.
(A) Choose the correct alternative (a), (b), (c) or (d) for each of the questions given below : [5×1] (i) The order of coloured rings in a carbon resistor is red, yellow, blue and silver. The resistance of the carbon resistor is
(a) 24 × 106 Ω ± 5%
(b) 24 × 106 Ω ± 10%
(c) 34 × 10Ω + 10%
(d) 26 × 104 Ω + 5%

(ii) A circular coil carrying a current I has radius R and number of turns N. If all the three, i.e., the current I, radius R and number of turns N are doubled, then, magnetic field at its center becomes:
(a) Double
(b) Half
(c) Four times
(d) One fourth


(iii) An object is kept on the principal axis of a concave mirror of focal length 10 cm, at a distance of 15 cm from its pole. The image formed by the mirror is:
(a) Virtual and magnified
(b) Virtual and diminished
(c) Real and magnified
(d) Real and diminished

(iv) Einstein’s photoelectric equation is :
(a) Emax = hλ – Φ0
(b) Emax = hc/λ – Φ0
(c) Emax = hv – Φ0
(d) Emax = hc/λ – Φ0
(v) In Bohr’s model of hydrogen atom, radius of the first orbit of an electron is r0. Then, radius of the third orbit is :
(a) r0/9
(b) r0
(c) 3r0
(d) 9r0

(B) Answer the following questions briefly and to the point [7 × 1] (i) In a potentiometer experiment, balancing length is found to be 120 cm for a cell E1 of emf 2 V What will be the balancing length for another cell E2 of emf 1.5V? (No other changes are made in the experiment.)
(ii) How will you convert a moving coil galvanometer into a voltmeter ?
(iii) A moving charged particle q.travelling along the positive x-axis enters a uniform magnetic field B. When will the force acting on q be maximum ?
(iv) Why is the core of a transformer laminated ?
(v) Ordinary (i.e.. unpolarised) light is incident on the surface of a transparent material at the polarising angle. If it is partly reflected and partly refracted, what is the angle between the reflected and the refracted rays ?
(vi) Define coherent sources of light.
(vii) Name a material which is used in making control rods in a nuclear reactor.

Answer 1.
(i) (c)
(ii) (a)
(iii) (c)
(iv) (b)
(v) (c)

(i) L1 = 120 cm, E1 = 2v, L2 = ?, E2 = 1.5 V
Using \frac{E_{2}}{E_{1}}=\frac{L_{2}}{L_{1}} \Rightarrow L_{2}=\frac{1.5}{2} \times 120=90 \mathrm{cm}
(ii) A moving coil galvanometer can be converted into a voltmeter by connecting a very high resistance in series with the galvanometer.
(iii) The force experienced by the charge is given by F = Bqv sin θ. where θ is the angle between the velocity vector and the magnetic field. For maximum force θ = 90 °
(iv) It is laminated to reduce the effects of eddy currents.
(v) 90°
(vi) Coherent sources of light are those sources which have zero or constant phase difference.
(vii) Boron and cadmium.

Section – B

Answer all questions

ISC 2018 Class-12 Physics Previous Year Question Papers Solved

Question 2.
Define current density. Write an expression which connects current density with drift speed.
Answer 2.
It is defined as the current flowing per unit area. The relation J = v ne.

Question 3. [2]
(a) A long horizontal wire P carries a current of 50 A. It is rigidly fixed. Another wire Q is placed directly above and parallel to P as shown in Figure 1 below. The weight per unit length of the wire Q is 0.025 N m-m and it carries a current of 25 A. Find the distance r of the wire Q from the wire P so that the wire Q remains at rest.
ISC Class 12 Physics Previous Year Question Papers Solved 2018 29

(b) Calculate force per unit length acting on the wire B due to the current flowing in the wire A. (See figure 2 below):
ISC Class 12 Physics Previous Year Question Papers Solved 2018 30
Answer 3.
ISC Class 12 Physics Previous Year Question Papers Solved 2018 31
Question 4. [2]
(i) Explain Curie’s law for a para magnetic substance.
(ii) A rectangular coil having 60 turns and area of 0.4 m2 is held at right angles to a uniform magnetic field of flux density’ 5 × 1o-5 T. Calculate the magnetic flux passing through it.
Answer 4.
(i) According to Curie’s law, the magnetization in a para magnetic material is directly proportional to the applied magnetic field. If the object is heated, the magnetization is viewed to be inversely proportional to the temperature.
It can be framed into an equation
M = C × (B/T)
wherein, M = Magnetism,
B = Magnetic field (in tesla),
T = absolute temperature (in kelvin),
C = Curie constant
Curie’s law holds good for high temperature and not so strong magnetic fields.
(ii) \begin{array}{l}{\text { Given } n=60, \mathrm{A}=0.4 \mathrm{m}^{2}, \theta=0^{\circ}, \mathrm{B}=5 \times 10^{-5} \mathrm{T}, \phi=?} \\ {\phi=n \mathrm{BA} \cos \theta=60 \times 5 \times 10^{-5} \times 0.4 \times 1=1.2 \times 10^{-3} \mathrm{Wb}}\end{array}

Question 5.
What is motional emf ? State any two factors on which it depends. [2] Answer 5.
It is the emf induced in a coil when there is relative motion between the coil and the magnet. It depends upon
(i) Number of turns in the coil.
(ii) relative velocity between the coil and the magnet.

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