ISC Class 12 Physics Question Paper Solution 2017

The ISC Class 12 Physics – Paper I (Theory) was conducted on 1st March 2017. The exam started at 2 PM. The paper was of 3 hours of time duration and 70 Marks. Here, we have provided the ISC Class 12 Physics Question Paper Solution 2017 to help students with their exam preparation. These previous years ISC Class 12 Physics Question Papers will give an idea of question paper design, the difficulty level of the exam and types of questions asked in the exam. Students can download the ISC Class 12 Physics Question Paper and Solution pdf 2017 from the link below.

Students can also access the Solved ISC Class 12 Previous Year Question Papers for Maths, Physics, Chemistry and Biology subjects compiled at one place. They can have a look at the ISC Class 12 Physics Question Paper Solution 2017 below.

Difficult Topics of ISC Class 12 Physics Paper 2017

Topics which students found difficult while solving the Physics 2017 paper are mentioned below:

• Capacitors in series and parallel.
• Derivation of electric potential at a point.
• Resistors in series and parallel.
• Numerical problems on electric circuits, voltmeter, meter bridge, etc.
• Angle of dip.
• Ampere circuital law: applications.
• Derivation of lens maker’s formula.
• Resolving power of a telescope.
• Energy level diagram of H atom.
• Depletion region

Confusing ISC Class 12 Physics Questions 2017

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

• Kirchoff’s 1st law and II law.
• Biot Savart’s law and Ampere’s circuital law.
• Spherical aberration and chromatic aberration.
• Lens formula and lens maker’s formula.
• Arranging electro-magnetic waves according to their frequencies.
• Emission spectrum and absorption spectrum of hydrogen atom.
• Characteristic X rays and continuous X rays.
• B.E and Binding Energy per nucleon.
• Forward bias and reverse bias of a junction diode.
• Frequency (f) and angular frequency (ω).

ISC Class 12 Physics Question Paper Solution 2017

Question 1:

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

(i) The electrostatic-potential energy of two point charges, 1 μC each, placed 1 meter apart in the air is:

1. 9×10³J
2. 9×10⁹J
3. 9×10^-3J
4. 9×10^-3eV

(ii) A wire of resistance ‘R’ is cut into ‘n’ equal parts. These parts are then connected in

parallel with each other. The equivalent resistance of the combination is:

1. nR
2. R/n
3. n/R²
4. R/n²

(iii) Magnetic susceptibility of platinum is 0·0001. Its relative permeability is:

1. 1.0000
2. 0.9999
3. 1.0001
4. 0

(iv) When a light wave travels from air to glass:

1. its wavelength decreases.
2. its wavelength increases.
3. there is no change in wavelength.
4. its frequency decreases.

(v) A radioactive substance decays to I/16th of its initial mass in 40 days. The half life of the substance, in days, is:

1. 20
2. 10
3. 5
4. 2·5

8. Answer all questions given below briefly and to the point:

(i) Maximum torque acting on an electric dipole of moment 3×10^-29 Cm in a uniform electric field E is 6x 10^-25 Nm. Find E.

(ii) What is meant by drift speed of free electrons?

(iii) On which conservation principle is Kirchhoff’s Second Law of electrical networks based?

(iv) Calculate magnetic flux density of the magnetic field at the centre of a circular coil of 50 turns, having radius of 0.5m and carrying a current of 5 A.

(v) An ac generator generates an emf ε where ε = 314 Sin(50πt) volt. Calculate the frequency of the emf ε.

(vi) With what type of source of light are cylindrical wave fronts associated?

(vii) How is fringe width of an interference pattern in Young’s double slit experiment affected if the two slits are brought closer to each other?

(viii) In a regular prism, what is the relation between angle of incidence and angle of emergence when it is in the minimum deviation position?

(ix) A converging lens of focal length 40 cm is kept in contact with a diverging lens of focal length 30 cm. Find the focal length of the combination.

(x) How can the spherical aberration produced by a lens be minimised?

(xi) Calculate the momentum of a photon of energy 6x 10^-19J.

(xii) According to Bohr, ‘Angular momentum of an orbiting electron 1s quantised’. What is meant by this statement?

(xiii) Why nuclear fusion reaction is also called thermo-nuclear reaction?

(xiv) What is the minimum energy which a gamma ray photon must possess in order to produce an electron-positron pair?

(xv) Show the variation of voltage with time, for a digital signal.

Answer:

A. (i) (c) OR 9×10^-3J

(ii) (d) OR R/n²

(iii) (c) OR 1·0001

(iv) (a) OR Its wavelength decreases.

(v) (b) OR 10 days

B. (i) E = 𝝉/𝑷 = 6×10^-25 / 3×10^-29 = 2×10⁴ 𝑽𝒎^−𝟏 or answer expressed with any alternate correct unit.

(ii) It is the mean distance travelled by a free electron per unit time (second) when an external electric field is applied. Or constant/average speed/velocity on application of potential difference/electric field or voltage or opposite to current or towards +ve terminal.

(iii) Energy

(iv)

(v) ω = 50π

or 2 π f = 50 π

∴ f = 25 Hz

(vi) Line source/ linear

(vii) Fringe width increases

(viii) They are equal, i.e.∠ i = ∠e

(ix)

(x) By using plano-convex / concave lenses

OR

With the help of stops. (A diagram showing a lens and a stop is also acceptable)

(xi) P = E/C = 6×10^-19 / 3×10⁸ = 2×10^-27 kg m s^-1 or answer expressed with any alternate correct unit.

(xii) It means angular momentum is an integral multiple of ђ OR h/2π

OR

l = nђ = nh/2π where n is an integer.

OR

mvr = nh/2π

(xiii) This is because a lot of heat energy is required to bring about nuclear fusion.

OR

A very high temperature is required to bring about nuclear fusion.

(xiv) 1·02 MeV OR 1.632 x 10^-13J.

(xv)

Question 2:

(a) Show that electric potential at a point P, at a distance ‘r’ from a fixed point charge 𝑄, is given by:

(b) Intensity of electric field at a perpendicular distance of 0·5 m from an infinitely long line charge having linear charge density (λ) is 3·6×10³ Vm^-1. Find the value of λ.

Answer: (a)

(b)

Question 3:

(a) Three capacitors C₁ = 3𝜇F, C₂ = 6𝜇F and C₃ = 10𝜇F are connected to a 50 V battery as shown in the Figure 1 below:

Calculate:

(i) The equivalent capacitance of the circuit between points A and B.

(ii) The charge on C₁.

(b) Two resistors R₁= 60 Ω and R₂ = 90 Ω are connected in parallel. If electric power consumed by the resistor R₁ is 15 W, calculate the power consumed by the resistor R₂.

Answer:

Question 4:

(a) Figure 2 below shows two resistors R₁ and R₂ connected to a battery having an emf of 40V and negligible internal resistance. A voltmeter having a resistance of 300 Ω is used to measure potential difference across R₁. Find the reading of the voltmeter.

(b) A moving coil galvanometer has a coil of resistance 59Ω. It shows a full-scale deflection for a current of 50 mA. How will you convert it to an ammeter having a range of 0 to 3A?

Answer:

Question 5:

(a) In a meter bridge circuit, resistance in the left hand gap is 2 Ω and an unknown resistance X is in the right hand gap as shown in Figure 3 below. The null point is found to be 40cm from the left end of the wire. What resistance should be connected to X so that thenew null point is 50 cm from the left end of the wire?

(b) The horizontal component of earth’s magnetic field at a place is 𝟏/√𝟑 times the vertical component. Determine the angle of dip at that place.

Answer:

Question 6:

(a) Using Ampere’s circuital law, obtain an expression for the magnetic flux density ‘B’ at a point ‘X’ at a perpendicular distance ‘r’ from a long current carrying conductor. (Statement of the law is not required).

(b) PQ is a long straight conductor carrying a current of 3A as shown in Figure 4 below. Anelectron moves with a velocity of 2×107 ms-1 parallel to it. Find the force acting on the electron.

Answer:

Question 7:

(a) (i) AB and CD are two parallel conductors kept l m apart and connected by a resistanceR of 6 Ω, as shown in Figure 5 below. They are placed in a magnetic field B = 3×10^-2 T which is perpendicular to the plane of the conductors and directed into the paper. A wire MN is placed over AB and CD and then made to slide with a velocity 2 ms^-1. (Neglect the resistance of AB, CD, and MN.)

Calculate the induced current flowing through the resistor R.

(ii) In an ideal transformer, an output of 66 kV is required when an input voltage of 220V is available. If the primary has 300 turns, how many turns should the secondary have?

(b) In a series LCR circuit, obtain an expression for the resonant frequency.

Answer:

Question 8:

(a) (i) State any one property which is common to all electromagnetic waves.

(ii) Arrange the following electromagnetic waves in increasing order of their frequencies (i.e. begin with the lowest frequency):

Visible light, 𝜸𝜸 rays, X rays, microwaves, radio waves, infrared radiations and ultraviolet radiations.

(b) (i) What is meant by diffraction of light?

(ii) In Fraunhofer diffraction, what kind of source of light is used and where is it situated?

Answer: (a) (i)

• All electromagnetic waves can travel through vacuum/ free space.
• They all have 𝑬, 𝑩 and 𝑪 vectors mutually perpendicular to each other.
• Transverse in Nature.
• They do not require a material medium for propagation.
• They can be reflected.
• All waves are produced by accelerated charged particles/oscillating charged particles.

(ii) Correct order is:

Radio waves, Microwaves, Infra-red radiations, visible light, ultra violet radiations, X-rays and γ rays.

(b) (i) Spreading or bending of light waves around the edges of an opaque aperture/obstacle/corner/around a body is called ‘diffraction’ of light.

(ii) Monochromatic source of light and it is situated far away. (i.e. at infinity)

Question 9:

(a) In Young’s double slit experiment using monochromatic light of wavelength 600 nm,5th bright fringe is at a distance of 0·48 mm from the centre of the pattern. If the screenis at a distance of 80 cm from the plane of the two slits, calculate:

(i) Distance between the two slits.

(ii) Fringe width, i.e. fringe separation.

(b) (i) State Brewster’s law.

(ii) Find Brewster’s angle for a transparent liquid having refractive index 1·5.

Answer: (a)

(b) (i) When ordinary (unpolarised) light is incident on a transparent medium at an angle of tan^-1 (𝜇), the reflected light is completely polarised.

(ii) θ_P = tan^-1 (1·50) = 56·3^o

Question 10:

(a) Find critical angle for glass and water pair, given refractive index of glass is 1·62 and that of water is 1·33.

(b) Starting with an expression for refraction at a single spherical surface, obtain Lens Maker’s Formula.

Answer: (a)

(b)

Question 11:

(a) A compound microscope consists of two convex lenses of focal length 2 cm and 5 cm.When an object is kept at a distance of 2·1 cm from the objective, a virtual and magnified image is formed 25 cm from the eye piece. Calculate the magnifying power of the microscope.

(b) (i) What is meant by resolving power of a telescope?

(ii) State any one method of increasing the resolving power of an astronomical telescope.

Answer: (a)

(b) (i) It is the ability of a telescope to form separate images of two distant objects. (close to each other.)

(ii) By increasing the diameter or aperture of the objective.

Question 12:

(a) (i) Plot a labelled graph of |𝑉𝑠| where 𝑉𝑠 is stopping potential versus frequency f of the incident radiation.

(ii) State how you will use this graph to determine the value of Planck’s constant.

(b) (i) Find the de Broglie wavelength of electrons moving with a speed of 7×10⁶ m s^-1.

(ii) Describe in brief what is observed when moving electrons are allowed to fall on a thin graphite film and the emergent beam falls on a fluorescent screen.

Answer:

(ii) Alternate bright and dark Circular fringes

Diffraction is seen/ alternate dark and bright figure /scintillation

Or any correct alternative answer.

Question 13:

(a) Draw an energy level diagram for the hydrogen atom, showing the first four energy levels corresponding to n = 1, 2, 3 and 4. Show transitions responsible for:

(i) Absorption spectrum of Lyman series.

(ii) Emission spectrum of Balmer series.

(b) (i) Find maximum frequency of X-rays produced by an X-ray tube operating at a tube potential of 66 kV.

(ii) State any one difference between characteristic X-rays and continuous X-rays.

Answer:

(ii)

1. Characteristic X rays are characteristic of the material of the target whereas continuous X rays are not.
2. Characteristic X rays are fewer in number whereas continuous X rays are infinite in number.
3. Continuous X rays have lower intensities whereas characteristic X rays have higher intensities.
4. λ_min of continuous X rays depends on applied voltage whereas λ of characteristic X-rays does not.

Question 14:

(a) Obtain a relation between half life of a radioactive substance and decay constant (λ).

(b) Calculate mass defect and binding energy per nucleon of ²⁰₁₀Ne, given

Mass of ²⁰₁₀Ne = 19.992397 u

Mass of ¹₁H = 1.007825 u

Mass of ¹₀n = 1.008665 u

Answer: (a)

(b)

Question 15:

(a) With reference to a semiconductor diode, what is meant by:

(i) Forward bias

(ii) Reverse bias

(iii) Depletion region

(b) Draw a diagram to show how NAND gates can be combined to obtain an OR gate. (Truth Table is not required).

Answer: (a) (i) Forward bias: It means p region is connected to positive terminal and n region is connected to negative terminal of a cell / battery.

OR

OR

(ii) Reverse bias: It means p region is connected to negative terminal and n region is connected to positive terminal of a cell/battery

OR

OR

(iii) Depletion region is a charge free region between p and n regions of a semiconductor diode.

It is a narrow space (region) between p and n regions which does not contain charge carriers (i.e. electrons and holes).

(b)

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