ISC Physics 2019 Class-12 Solved Previous Year Question Paper for practice. Step by step Solutions with section-A, B, C and D. Visit official website CISCE for detail information about ISC Class-12 Physics.

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Section-A

Section-B

Section-C

Section-D

### Class-12 Solved Previous Year Question Paper ISC Physics 2019

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

( ISC Physics 2019 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 × 1]
(i) A closed surface in vacuum encloses charges -q and +3 q. The total electric flux emerging out of the surface is :
(a) Zero
(b) $\frac{2 q}{\epsilon_{o}}$
(c) $\frac{3 q}{\epsilon_{0}}$
(d) $\frac{4 q}{\epsilon_{0}}$

(A) (i) (b)

(ii). What is the angle of dip at a place where the horizontal component (BH) and vertical component (BV) of earth’s magnetic field are equal:
(a) 130°
(b) 60°
(c) 45°
(d) 90°

(A)
(ii) (c)
(iii). A beam of light is incident at the polarizing angle of 35° on a certain glass plate. The refractive index of the glass plate is :

(a) sin 35°
(b) tan 35°
(c) tan 55°
(d) sin 55°

(A)
(iii) (b)

(iv). In a gamma ray emission from nucleus :
(a) only the number of protons change.
(b) the number of protons and neutrons, both change.
(c) there is no change in the number of protons and the number of neutrons.
(d) only the number of neutrons change

(A)
(iv) (c)

(v). The energy associated with light of which of the following colours is minimum
(a) violet
(h) red
(c) green
(d) yellow

(A)
(v) (a)

(B) Answer the following questions briefly and to the point. [7 × 1]
(i) Define equipotential surface.

Answer :- An equipotential surface is one on the surface of which the potential is same.

(ii) Calculate the net emf across A and B shown in Figure 1 below : (iiii) Why are the pole pieces of a horseshoe magnet in a moving coil galvanometer made cylindrical in shape ?

(iv) What is the value of power factor for a pure resistor connected to an alternating current source ?

(v) What should be the path difference between two waves reaching a point for obtaining constructive interference in Young’s Double Slit experiment.

(vi) Define critical angle for a given medium.

Answer- It is defined as the angle of incidence in the denser medium for which the angle of refraction in the rarer medium is 90°.

(vii) Name the series in the atomic spectra of the hydrogen atom that falls in the ultraviolet region.

### Section – B

( ISC Physics 2019 Class-12 Solved Previous Year Question Paper )

Question 2. 
In a potentiometer experiment, the balancing length with a resistance of 2 Ω is found to be 100 cm, while that of an unknown resistance is 500 cm. Calculate the value of the unknown resistance.
Given R1 =2Ω ,L1 = 100 cm, L2= 500 cm, R2 = ?
Using the expression $\frac{E_{2}}{E_{1}}=\frac{L_{2}}{L_{1}}=\frac{R_{2}}{R_{1}} \Rightarrow R_{2}=\frac{L_{2} R_{1}}{L_{1}}=\frac{500 \times 2}{100}=10 \Omega$

Question 3. 
A rectangular loop of area 5 mH. has 50 turns and carries a current of 1 A. It is held in a uniform magnetic field of 0. IT, at an angle of 30°. Calculate the torque experienced by the coil.
Given, A= 5 m2, n = 50, I = 1 A, B = 0.1T, θ= 30°, T= T $\mathrm{T}=\mathrm{B} \ln \mathrm{A} \sin \theta=0.1 \times 1 \times 50 \times 5 \times \sin 30^{\circ}=12.5 \mathrm{Nm}$

Question 4. 
(a) A electric current I flows through an infinitely long conductor as shown in Figure 2(a) below. Write an expression and direction for the magnetic field at point P.  $\mathrm{B}=\frac{\mu_{0} \mathrm{I}}{2 \pi r}$ , perpendicular to the plane of the paper and directed inwards.
(b) An electric current I flows through a circular loop as shown in Figure 2(b) below. Write an expression and direction for the magnetic field at the centre of the loop at point P.  $\mathrm{B}=\frac{\mu_{0} \mathrm{I}}{2 r}$ , perpendicular to the plane of the paper and directed outwards.

Question 5. 
A transformer is used to step up an alternating emf of 200 V to 440 V. If the primary coil has 1000 turns, calculate the number of turns in the secondary coil. Question 6. 
State any two properties of microwaves.

• They move with the speed of light.
• They can heat matter.

Question 7. 
Write any one use for each of the following mirrors :
(a) Convex
(b) Concave
(a) Used as a rear view mirror.
(b) Used as a shaving mirror.

Question 8. 
The deviation produced for violet, yellow and red lights for crown glass are 3.75°. 3.25° and 2.86° respectively. Calculate the dispersive power of the crown glass.
Given δV = 3.75°, δY = 3.25°, δR = 2.86°
Using the expression for dispersive power $\mathrm{D} \mathrm{P}=\frac{\delta_{\mathrm{V}}-\delta_{\mathrm{R}}}{\delta_{\mathrm{Y}}}=\frac{3.75-2.86}{3.25}=0.27$

Question 9. 
(a) What is meant by mass defect ?

This is the difference in mass of the constituent nucleons and the nucleus formed.

(b) What conclusion is drawn from Rutherford’s scattering experiment of α -particles ?

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