ISC Physical Science Class XII 2023

ISC Physical Science

Class – XII (2023)

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.

Question 1.

A. In questions (i) to (vii) given below, choose the correct alternative (a), (b), (c) or (d) for each of the questions.

(i) A hollow sphere of radius R has a point charge Q at its centre. Electric flux emanating from it is 𝜑. If both the charge and the radius of the sphere be doubled, electric flux emanating from the sphere will:

a) Remain the same.

b) Become 2𝜑

c) Become 4𝜑

d) Become 8𝜑

Solution

(ii) An electric current (I) flowing through a metallic wire is gradually increased. The graph of heating power (P) developed in it versus the current (I) is:

a)

b)

c)

d)

Solution

(iii) A circular coil has radius ‘ r ‘, number of turns ‘ N ‘ and carries a current ‘ l ‘. Magnetic flux density ‘ B ‘ at its centre is:

(a) 𝐵 = 𝜇₀ 𝑁𝐼

(b) 𝐵 = 𝜇₀ 𝑁𝐼/2 𝑟

(c) 𝐵 = { \mu _o NI \over 4 \pi r}

(d) 𝐵 = 𝜇₀𝑁𝐼/4 𝑟

Solution

(iv) If an object is placed at a distance of 10 cm in front of a concave mirror of focal length 20 cm, the image formed will be:

(a) real and 20 cm in front of the mirror.

(b) real and 6.67 cm in front of the mirror.

(c) virtual and 20 cm behind the mirror.

(d) virtual and 6.67 cm behind the mirror.

Solution

(v) What type of wavefronts are associated with a source at infinity?

(a) Cylindrical wavefronts

(b) Plane wavefronts

(c) Spherical wavefronts

(d) All types of wavefronts

Solution

(vi) Matter waves are:

(a) Waves associated with moving particles.

(b) Waves associated with stationary particles.

(c) Waves associated with any charged particles.

(d) Waves associated with electrons only.

Solution

(vii) With an increase in the temperature, electrical conductivity of a semiconductor:

(a) Decreases.

(b) Increases.

(c) Does not change.

(d) First increases and then decreases.

Solution

B. Answer the following questions briefly.

(i) What is meant by an equipotential surface?

Solution

(ii) In case of metals, what is the relation between current density (J), electrical conductivity (𝜎) and electric field intensity (E)?

Solution

(iii) What is meant by “Motional emf”?

Solution

(iv) What is meant by a microscope in normal use?

Solution

(v) In a single slit Fraunhofer diffraction experiment, how does the angular width of central maximum change when the slit width is increased?

Solution

(vi) Name the type of nuclear reaction that takes place in the core of the Sun.

Solution

(vii) What type of semiconductor is obtained when a crystal of silicon is doped with a trivalent element?

Solution

Question 2.

(i) Calculate equivalent capacitance of the circuit shown in Figure 1 given below:

Solution

OR

(ii) Calculate electric potential at a point P which is at a distance of 9cm from a point charge of 50 μC.

Solution

Question 3.

(i) Write balancing condition of a Wheatstone bridge.

(ii) Current ‘I’ flowing through a metallic wire is related to drift speed 𝑉_𝑑 of free electrons as follows:

𝐼 = 𝑛𝐴𝑒𝑉_𝑑

State what symbol ‘n’ stands for.

Solution

Question 4.

When an electric current is passed through a wire or a coil, a magnetic field is produced. Is the reverse phenomenon possible i.e., can a magnetic field produce an electric current?

Explain with the help of an appropriate example.

Solution

Question 5.

(i) A long straight wire 𝐴𝐵 carries a current of 5𝐴. 𝑃 is a proton travelling with a velocity of 2 × 10⁶ 𝑚/𝑠, parallel to the wire, 0.2 𝑚 from it and in a direction opposite to the current, as shown in Figure 2 below. Calculate the force which magnetic field of the current carrying conductor AB exerts on the proton.

Solution

OR

(ii) A moving coil galvanometer of resistance 55Ω produces a full scale deflection for a current of 250 𝑚𝐴. How will you convert it into an ammeter having a range of 0 − 3𝐴?

Solution

Question 6.

(i) State how vectors 𝐸⃗ , 𝐵⃗ and 𝐶 are oriented in an electromagnetic wave

(ii) Name the electromagnetic wave / radiation which is used to study crystal structure.

Solution

Question 7.

Name any two phenomenon which takes place in the formation of a rainbow.

Solution

Question 8.

With reference to semiconductor physics, answer the following questions.

(i) What is meant by “Forbidden band” of energy levels?

(ii) In which material “Forbidden band” is absent?

Solution

Question 9.

Show that intensity of electric field at a point in broadside position of an electric dipole is given by:

({1\over 4 \pi \epsilon _o}){p \over {(r^2 + l^2)}^{3\over2}}

where the terms have their usual meaning.

Solution

Question 10.

(i) Eight identical cells, each of emf 2 V and internal resistance 3 Ω , are connected in series to form a row. Six such rows are connected in parallel to form a battery. This battery is now connected to an external resistor R of resistance 6 Ω. Calculate:

(a) emf of the battery.

(b) internal resistance of the battery.

(c) current flowing through R.

Solution

OR

(ii) In the circuit shown in Figure 3 below, 𝐸₁ and 𝐸₂ are batteries having emfs of 25 V and 26 V. They have an internal resistance of 1 Ω and 5 Ω respectively. Applying Kirchhoff’s laws of electrical networks, calculate the currents 𝐼₁ and  𝐼₂.

Solution

Question 11.

Using Ampere’s circuital law, obtain an expression for magnetic flux density ‘B’ at a point near an infinitely long and straight conductor, carrying a current I.

Solution

Question 12.

Using Huygen’s wave theory of light, show that the angle of incidence is equal to the angle of reflection. Draw a neat and labelled diagram.

Solution

Question 13.

(i) For any prism, obtain a relation between angle of the prism (A). angle of minimum deviation (𝛿_𝑚) and refractive index of its material (𝜇 𝑜𝑟 𝑛).

Solution

OR

(ii) Obtain an expression for refraction at a single convex spherical surface i.e., the relation between 𝜇₁ (rarer medium), 𝜇₂ (denser medium), object distance u. image distance v and the radius of curvature.

Solution

Question 14.

(i) What is the essential condition for obtaining a sustained interference?

(ii) In Young’s double slit experiment, the distance of the 4^th bright fringe from the centre of the interference pattern is 1.5mm. The distance between the slits and the screen is 1.5m and the wavelength of light used is 500nm. Calculate the distance between the two slits.

Solution

Question 15.

Monochromatic light of wavelength 396nm is incident on the surface of a metal whose work function is 1.125eV.

Calculate:

(i) the energy of an incident photon in eV.

(ii) the maximum kinetic energy of photoelectrons in eV.

Solution

Question 16.

Name any two essential parts of a nuclear reactor. State the function of any one of them.

Solution

Question 17.

Draw a labelled circuit diagram of a full wave rectifier. Show graphically how the output voltage varies with time.

Solution

Question 18.

(i) A 60Ω resistor, a 1.0 H inductor and 4𝜇F capacitor are connected in series to an ac supply generating an emf e = 300 sin (500t)V. calculate:

1. Impedance of the circuit.
2. Peak value of the current flowing through the circuit.
3. Phase difference between the current and the supply voltage.

Solution

OR

ii.

a) An ac generator generates an emf which is given by 𝑒 = 311 sin(240𝜋𝑡)𝑉.

Calculate:

1. Frequency of the emf.

2. r.m.s value of the emf.

b) The primary coil of a transformer has 60 turns whereas its secondary coil has 3000 turns.

1. If a 220 V ac voltage is applied to the primary coil, how much emf is induced in the secondary coil?

2. If a current of 5A flows in the primary coil, how much current will flow in a load in the secondary coil?

State the assumption you have made regarding the transformer, in this calculation.

Solution

Question 19.

1. (a) Name the series of lines of hydrogen spectrum which lies in the (1) ultraviolet region. (2) visible region.

(b) How much is the angular momentum of an electron when it is orbiting in the second Bohr orbit of a hydrogen atom?

(c) With reference to Nuclear Physics, answer the following questions.

(1) What is meant by “Isotopes”?

(2) Define 1u (where u stands for unified atomic mass unit).

Solution

OR

ii.

a) Using Bohr’s theory of hydrogen atom, obtain an expression for the velocity of an electron in nth orbit of an atom.

b) What is meant by Binding Energy per nucleon of a nucleus? State its physical significance.

Solution

Question 20.

Read the passage given below and answer the questions that follow.

There are two types of lenses: Converging lenses and Diverging lenses, depending on whether they converge or diverge an incident beam of light. They are also called convex or concave lenses. Lenses are usually made of glass. Convex lenses are more popular as they form a real image of an object. They are widely used in our daily life, for instance, in microscopes, telescopes, projectors, cameras, spectacles etc. Microscopes are used to view small and nearby objects whereas telescopes are used to see distant objects.

i. State any one factor on which focal length of a lens depends.

ii. Give an example where a convex lens behaves like a diverging lens.

iii. What type of lens is used in a camera?

iv. Write an expression for magnifying power of a compound microscope when its final image lies at the least distance of distinct vision (D).

v. State any one difference between a reflecting telescope and a refracting telescope.

Solution