ISC Physical Science 2019 Class XII

ISC Physical Science 2019

Max. Marks: 70

General Instructions

1. Candidates are allowed additional 15 minutes for only reading the paper. They must not start writing during this time.

2. All questions are compulsory. This question paper is divided into 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 question having internal choice.

Section C Question numbers 13 to 19 carry 3 marks each with two question having internal choice.

Section D Question numbers 20 to 22 are long answer type question and carry 5 marks each.

3. All working including rough work should be done on the same sheet and adjacent to the right of the answer.

4. The intended marks for questions or parts of question are given in brackets [ ]

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

SECTION A

Question 1.

A. Choose the correct alternative (a), (b), (c) and (d) for each of the question given below: [5×1].

(i)  A closed surface in vacuum enclose charges –q and +3q. The total electric  flux emerging out of the surface is

(a) Zero

(b) {2q \over 𝜺_0}

(c) {3q \over 𝜺_0}

(d) {4q \over 𝜺_0}

Solution

(ii)  What is the angle of dip at a place where the horizontal component BH and the vertical component BV of the earth’s magnetic field are equal to

(a) 130°

(b) 60°

(c) 45°

(d) 90°

Solution

(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) sin 55°

(d) tan 55°

Solution

(iv)  In a gamma ray emission from nucleus

(a) Only the number of proton change

(b) The number of proton and neutron both changes

(c) There is no change in the number of protons and the number of neutrons

(d) Only the number of neutrons changes

Solution

(v) The energy associated with light of which of the following colors in  minimum?

(a) Violet

(b) Red

(c) Green

(d) Yellow

Solution

B. Answer the following questions briefly and to the point.

(i)  Define equipotential surface.

Solution

(ii) Calculate the net emf across A and B shown in the figure below.

Solution

(iii) Why are the pole pieces of a horseshoe magnet in moving coil galvanometer  made cylindrical in shape?

Solution

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

Solution

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

Solution

(vi) Define the critical angle for the given medium.

Solution

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

Solution

SECTION B

Question 2. 

In a potentiometer experiment, the balancing length with a resistance of 2Ω is found to be 100cm, while that of unknown resistance is 500cm. calculate the value of the unknown resistance.

Solution

Question 3.

A rectangular loop of area 5m², has 50 turns and carries a current of 1A. It is held in a uniform magnetic field of 0.1T, at an angle of 30°. Calculate the torque experienced by the coil.

Solution

Question 4.

An electric current I flows through an infinitely long conductor as shown in the figure given below. Write an expression and direction for the magnetic field at point P.

Solution

Question 5.

A transformer is used to step up an alternating emf of 200V to 440V. If the primary coil has 1000 turns, calculate the number of turns in secondary coil.

Solution

Question 6.

State any two properties of microwaves.

Solution

Question 7.

Write any one use for each of the following mirrors.

(i) Convex

(ii) Concave

Solution

Question 8.

The deviation produced for violet, yellow and lights for crown glass are 3.75°, 3.25° and 2.86° respectively. Calculate the dispersive power of the crown glass.

Solution

Question 9.

(i) What is the meant by the mass defect?

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

Solution

Question 10.

Define the following with reference to photoelectric effect.

(i) Threshold frequency f₀

(ii) Stopping potential V_s

Solution

Question 11.

The half-life of radium is 1550yr. calculate its disintegration constant λ.

Solution

Question 12.

 Define frequency modulation and state any one advantage of frequency modulation (FM) over amplitude modulation (AM).

Solution

SECTION C

Question 13.

Obtain an expression for electric potential V at the point in an end-on position, axial position of an electric dipole.

Solution

Question 14.

Three capacitors o capacitance C₁ = 3μF, C₂ = 6μF and C₃ = 10μF are connected to a 10v battery as shown in the figure given below.

(i) Equivalent

(ii) Electrostatic potential energy stored in the system.

Solution

Question 15.

Draw a labelled circuit diagram of a potentiometer to measure the internal resistance r of a cell. Write the working formula (deviation is not required).

Solution

Question 16.

A ray of light is incident on a prism whose refraction index is 1.52 at an angle of 40°. If the angle of emergence is 60°, calculate the angle of the prism.

Solution

Question 17.

Derive the law of reflection using Huygens’s wave theory.

Solution

Question 18.

State any two Bohr’s postulates and write the energy value of the ground state of the hydrogen atom.

Solution

Question 19.

With reference to semiconductor answer the following.

(i) What is the change in the resistance of the semiconductor with increase in  temperature?

(ii) Name the majority charge carries in n-type semiconductor.

(iii) What is meant by doping?

Solution

SECTION D

Question 20.

(i) An alternating emf of 200V, 50Hz is applied to an L-R circuit, having a resistance R of 10Ω and an inductance L of 0.o5H connected in series. Calculate.

(a) Impedance

(b) Current flowing in the circuit.

(ii)Draw a labelled graph showing the variation of inductive reactance X_L versus frequency f.

Solution

Question 21.

Draw a neat labelled ray diagram showing the formation of an image at the least  distance of distinct vision D by a simple microscope. When the final image is at D, derive an expansions for its magnifying power at D.

Solution

Question 22.

(I) Draw a labelled circuit diagram of a half-wave rectifier and give its output waveform.

(II) Draw a symbol for NOR gate and write its truth table.

Solution