ISC Class 12 Physics Question Paper Solution 2016

The ISC Class 12 Physics – Paper I (Theory) was conducted on 4th March 2016. The exam started at 2 PM. The paper was of 3 hours of time duration and 100 Marks. Here, students can find the solved ISC Class 12 Physics Question Paper 2016 along with the marking scheme. They can download the ISC Class 12 Physics Question Paper Solution pdf 2016 from the link provided below. Solving the previous years ISC Class 12 Physics Question Papers and then referring to the solution pdf will help students in analysing their preparation level. So, go through the Solution pdf and make the most of it.

For students convenience, we have also compiled the solved ISC Class 12 Previous Year Question Papers of Maths, Physics, Chemistry and Biology subjects at one place. Students can download and access them for free. They can have a look at the ISC Class 12 Physics Question Paper Solution 2016 below.

Difficult Topics of ISC Class 12 Physics Paper 2016

Topics which students found difficult while solving the Physics 2016 paper are mentioned below:

− Intensity of electric field due to two point charges.

− Internal resistance of a cell by potentiometer.

− Kirchoffs’ Law.

− Neutral point due to two long current carrying conductors.

− Labelled ray diagram of an astronomical telescope.

− Range of wavelengths in an electromagnetic spectrum.

− Colour coding of carbon resistors.

− Einstein’s photoelectric equation.

− Bohr’s theory of spectrum of hydrogen

− Common emitter amplifier.

− Refraction of light through a prism.

− Width of central Maxima in Fraunhofer diffraction.

Confusing ISC Class 12 Physics Questions 2016

Physics concepts between which students got confused during the exam are mentioned below.

− Short Sightedness and Long sightedness.

− Polarised light and unpolarised light.

− Refraction of light and reflection of light based on Huygen’s wave theory.

− Ray diagram of astronomical telescope and compound microscope.

− Potentiometer and Wheatstone bridge.

− Conversion of Galvanometer into ammeter and voltmeter.

− Curie temperature and Curie’s Law

− Capacitors in series and parallel.

− Graph of Z vs f and phasors.

− Shortest and longest wavelength of Balmer series.

ISC Class 12 Physics Question Paper Solution 2016

Question 1:

A. Choose the correct alternative (a), (b), (c) or (d) for each of the questions given below:

(i) In Figure 1 below, a charge Q is fixed. Another charge q is moved along a circular arc MN of radius r around it, from the point M to the point N such that the length of the arc MN = l. The work done in this process is:

(ii) A carbon resistor has coloured bands as shown in Figure 2 below. The resistance of the resistor is:

1. 26Ω ± 10%
2. 26Ω ± 5%
3. 260Ω ± 5%
4. 260Ω ± 10%

(iii) A solenoid L and a resistor R are connected in series to a battery, through a switch. When the switch is put on, current I flowing through it varies with time t as shown in which of the graphs given below:

(iv) Two thin lenses having optical powers of -10D and + 6D are placed in contact with each other. The focal length of the combination is:

1. + 0·25 cm
2. – 0·25 cm
3. + 0·25 m
4. – 0·25 m

(v) Total energy of an electron in the ground state of hydrogen atom is -13·6 eV. Its total energy, when hydrogen atom is in the first excited state, is:

1. + 13·6 eV
2. + 3·4 eV
3. – 3·4 eV
4. – 54·4 eV

B. Answer all questions given below briefly and to the point:[15]

(i) A charged oil drop weighing 1·6 × 10^-15 N is found to remain suspended in a uniform electric field of intensity 2 × 10³ NC^-1. Find the charge on the drop.

(ii) For a metallic conductor, what is the relation between current density (J),conductivity (𝜎) and electric field intensity E?

(iii) In Figure 3 given below, find the value of resistance x for which points A and B are at the same potential:

(iv) Write the expression for the Lorentz force F in vector form.

(v) A coil has a self-inductance of 0·05 Henry. Find the magnitude of the emf induced in it when the current flowing through it is changing at the rate 100 As-1.

(vi) To which regions of the electromagnetic spectrum do the following wavelengthsbelong:

1. 250 nm
2. 1500 nm

(vii) What is the difference between polarised light and unpolarised light?

(viii) Name the principle on the basis of which optical fibres work.

(ix) Calculate dispersive power of a transparent material given:

n_v = 1·56 , n_r = 1·54, n_y = 1·55.

(x) What is meant by short-sightedness?

(xi) Two metals A and B have work functions 4eV and 6eV respectively. Which metal has lower threshold wavelength for photoelectric effect?

(xii) Calculate angular momentum of an electron in the third Bohr orbit of hydrogen atom.

(xiii) In a nuclear reactor, what is the function of a moderator?

(xiv) In our Nature, where is the nuclear fusion reaction taking place continuously?

(xv) What is the use of a Zener diode?

Answer: A. (i) (a) or zero

(ii) (c) or 260(Ω) ± 5%

(iii) (b) or

(iv) (d) or − 0·25 m

(v) (c) or − 3·4 (eV)

B. (i) q=𝑭/𝑬= 1.6×10^-15 / 2×10³ = 8 ×10⁻¹⁹ C or 5e

(ii) J = 𝜎E OR ȷ⃗=𝜎𝐸

(iii) 3/6 = 5/x ⇒x = 10Ω OR

𝟑/𝟓 = 𝟔/𝒙 ⇒x = 10Ω OR

x = 10 Ω, directly, since it is a balanced Wheatstone bridge

(iv) 𝐹⃗ = q(𝑣⃗×𝐵) OR q(𝑣⃗×𝐵) OR q(𝐸 +𝑣⃗×𝐵)

(v)

(vi)

1. Ultra violet or uv (region)
2. Infra-red or IR (region)

(vii) In unpolarised light, electric vector (or 𝐸) points in infinite (or many) directions, all perpendicular to 𝑐⃗ (or direction of propagation) whereas in polarised light, it points in one direction only.

(viii) Total internal reflection (or T.I.R. or t.i.r.)

(ix)

(x) It is that defect of vision in which a person:

1. Is unable to see distant objects
2. Can see nearby objects only

(xi) B

(xii)

(xiii) It slows down fast moving neutrons. Or

It converts high speed neutrons to slow neutrons Or

It produces thermal neutrons. Or

It converts high energy neutrons to slow moving or thermal neutrons.

(xiv) Sun or a star

(xv) It is used for voltage regulation Or

It is used as a voltage regulator Or

It is used as a voltage stabilizer Or

It converts a fluctuating voltage to a steady voltage.

Question 2:

Question 2

(a) Two point charges Q1 = 400μC and Q2 = 100μC are kept fixed, 60 cm apart in vacuum.Find intensity of the electric field at the midpoint of the line joining Q1 and Q2.

(b) (i) State Gauss’ Law.

(ii) In an electric dipole, at which point is the electric potential zero?

Answer:

(ii) (A point) in broad side position OR

(A point) in an equatorial plane OR

(A point) on an equatorial line OR

(A point) on perpendicular bisector of the dipole or centre or mid-point

Question 3:

(a) Obtain an expression for equivalent capacitance when three capacitors C₁, C₂ and C₃ are connected in series.

(b) A metallic wire has a resistance of 3·0Ω at 0^oC and 4·8Ω at 150^oC. Find the temperature coefficient of resistance of its material.

Answer:

Question 4:

(a) In the circuit shown in Figure 4 below, E₁ and E₂ are two cells having emfs 2V and 3V respectively, and negligible internal resistances. Applying Kirchoff’s laws of electrical networks, find the values of currents I₁ and I₂.

(b) State how a moving coil galvanometer can be converted into an ammeter.

Answer:

Question 5:

(a) Draw a labelled circuit diagram of a potentiometer to measure internal resistance of acell. Write the working formula. (Derivation not required).

(b) (i) Define Curie temperature.

(ii) If magnetic susceptibility of a certain magnetic material is 0·0001, find its relative permeability.

Answer: (a)

(b) (i) It is that temperature at which a ferromagnetic material becomes paramagnetic.

OR

That temperature at which its magnetic susceptibility becomes slightly greater than zero.

(ii) μ_𝒓 = 1 + x

OR

μ_𝒓 = 1 + 0.0001 = 1.0001

Question 6:

(a) (i) Two infinitely long current carrying conductors X and Y are kept parallel to each other, 24 cm apart in vacuum. They carry currents of 5A and 7A respectively, in the same direction, as shown in Figure 5 below. Find the position of a neutral point, i.e. a point where resultant magnetic flux density is zero. (Ignore earth’s magnetic field).

(ii) If the current through the conductor Y is reversed in direction, will the neutral point lie between X and Y, to the left of X or to the right of Y?

(b) (i) Define Ampere in terms of force between two current carrying conductors.

(ii) What is an ideal transformer?

Answer: (a)(i)

(ii) It will lie to the left of X

(Neutral point always lies near a weaker current).

(b) (i) It is that current which while flowing through two (thin) (infinitely) long current carrying conductors kept parallel to each other 1m apart in vacuum, attract or repel each other with 2×10^-7 N(m^-1).

(i) Two conductors are kept parallel to each other.

(ii) Two conductors are kept 1 m apart

(iii) Two conductors are kept in vacuum

(iv) They attract or repel each other with 2×10^-7 N(m^-1).

A labelled diagram indicating at least three of the above said (four) may be accepted as an answer.

(ii) It is that in which there is no loss of any power. OR

It is that where output power = input power. OR

It is that whose efficiency is 1. OR

It is that in which electric power across secondary is equal to electric power across primary.

Question 7:

(a) A coil having self-inductance of 0·7H and resistance of 165Ω is connected to ana.c.source of 275V, 50Hz. If 𝜋𝜋=227,

Calculate:

(i) Reactance of the coil

(ii) Impedance of the coil

(iii) Current flowing through the coil

(b) Draw a labelled graph showing variation of impedance of a series LCR circuit with frequency of the a.c. supply.

Answer:

Question 8:

(a) Derive Snell’s law of refraction using Huygens wave theory.

(b) Monochromatic light of wavelength 650nm falls normally on a slit of width 1·3 × 10^-4 cm and the resulting Fraunhofer diffraction is obtained on a screen. Find the angular width of the central maxima.

Answer: (a) Correct diagram with i and r shown correctly with an arrow on either incident ray or refracted ray or incident wavefront and refracted wavefront mentioned in the diagram or the text.

(b)

Question 9:

(a) In Young’s double slit experiment, show that:

𝛽 =𝜆D/𝑑,

where the terms have their usual meaning.

(b) A ray of ordinary light is travelling in air. It is incident on an air glass pair at a polarising angle of 56^o. Find the angle of refraction in glass.

Answer:

(b) At a polarising angle, reflected ray and refracted ray are perpendicular to each other.

56 + r = 90^o and

∴ r = 90 – 56 = 34^o

Question 10:

(a) Find the angle of incidence at which a ray of monochromatic light should be incident on the first surface AB of a regular glass prism ABC so that the emergent ray grazes the adjacent surface AC. (Refractive Index of glass = 1·56).

(b) State how focal length of a glass lens (Refractive Index 1·5) changes when it iscompletely immersed in:

(i) Water (Refractive Index 1·33)

(ii) A liquid (Refractive Index 1·65)

Answer: (a)

(b) (i) Focal length of the lens increases.

(ii) Focal length of the lens becomes –ve OR

The convex lens behaves like a diverging lens and vice versa.

Nature of lens changes.

Question 11:

(a) A convex lens of a focal length 5 cm is used as a simple microscope. Where should an object be placed so that the image formed by it lies at the least distance of distinct vision (D=25cm)?

(b) Draw a labelled ray diagram showing the formation of an image by a refracting telescope when the final image lies at infinity.

Answer: (a)

Method 1: (Sign convention: Real is +ve and Virtual is –ve)

(b) (i) Correct incident rays (i.e. parallel and oblique) with an arrow on any one of them incident

on 1st lens and inverted image formed.

(ii) Correct emergent rays (i.e. parallel and oblique) with an arrow on at least one of them with rays produced back.

(iii) FO & Fe coinciding and either O or E marked in diagram.

Question 12:

(a) Monochromatic light of wavelength 198 nm is incident on the surface of a metallic cathode whose work function is 2·5 eV. How much potential difference must be applied between the cathode and the anode of a photocell to just stop the photo current from flowing?

(b) (i) What is de Broglie hypothesis?

(ii) What conclusion can be drawn from Davisson and Germer’s experiment?

Answer: (a)

Method 1: Correct formula

(b) (i) It states that moving particles, electrons, etc. behave like waves or show wave nature or dual nature and their wavelength varies inversely with their momentum.

Or formula λ= h/p, where p is momentum

λ = h/mv

(ii) (Moving) electrons or particles can be diffracted OR

(Moving) electrons or particles show wave nature OR

(Moving) electrons or particles are behaving like waves. OR

Dual nature of electrons/ particles OR

Confirms De Broglie hypothesis

Question 13:

(a) (i) How are various lines of the Lyman series formed? Explain on the basis ofBohr’s theory.

(ii) Calculate the shortest wavelength of electromagnetic radiation present inBalmer series of the hydrogen spectrum.

(b) State the effect of the following changes on the X-rays emitted by Coolidge X-ray tube:

(i) High voltage between cathode and anode is increased.

(ii) Filament temperature is increased.

Answers: (a) (i) Various lines of Lyman series are obtained when electrons of hydrogen atom jump from higher orbits to the first orbit. OR

Hydrogen atom(s) go(es) from excited state(s) to the ground state OR

A diagram showing es going from higher orbits to the 1st orbit. OR

Energy level diagram showing downward transitions from higher levels to the lowest level (for which n = 1) or vice versa

(ii)

(b) (i) More penetrating X-rays are obtained OR

Penetrating power of emitted X-rays increases OR

higher frequency X-rays are produced

More energetic X-rays are emitted, OR

Harder X-rays are obtained/emitted.

(ii) Intensity of emitted X-rays increases.

Number of X- ray photons/sec increases

Question 14:

(a) Half life of a certain radioactive material is 8 hours.

(i) Find the disintegration constant of this material.

(ii) If one starts with 600g of this substance, how much of it will disintegrate in one day?

(b) Sketch a graph showing the variation of binding energy per nucleon of a nucleus with its mass number.

Answers: (a) (i)

= 2·4 × 10-5 per second.

(ii) 1 day = 24 hrs = 3 T

Amount disintegrated = (600 – 75) = 525 g

(b) (i) Approximately correct shape

(ii) Correct labelling i.e. B.E./A on

Y axis and A on X axis

Question 15:

(a) Draw a circuit diagram for the common emitter transistor amplifier. What is meant by phase reversal?

(b) Write the truth table of the following circuit. Name the gate represented by this circuit.

Answers: (a) (Either PNP OR NPN transistor may be used by a pupil.)

(i)

Correct input circuit

Correct output circuit

Signal, grid bias and correct collector battery & load or output

(ii) When signal voltage is positive,

Output is –ve and

When signal voltage is –ve

Output is +ve.

This is called phase reversal.

OR

Input and output voltages are out of phase by 180o or 𝛑𝛑 rod

OR Correct diagram.

(b)

It represents AND gate OR symbol of AND gate.

The answers provided in ISC Class 12 Physics Question Paper Solution 2016 must have helped students in their exam preparation. So, be regular in your studies and keep working hard. Stay tuned to BYJU’S for the latest update on ICSE/CBSE/State Boards/Competitive exams. Also, download the BYJU’S App for interactive study videos.