Students must start practicing the questions from CBSE Sample Papers for Class 12 Physics with Solutions Set 9 are designed as per the revised syllabus.
CBSE Sample Papers for Class 12 Physics Set 9 for Practice
Time Allowed: 3 Hours
Maximum Marks: 70 Marks
General Instructions:
- There are 35 questions in all. All questions are compulsory.
- This question paper has five sections: Section A, Section B, Section C, Section D and Section E. All the sections are compulsory.
- Section A contains eighteen MCQ of 1 mark each, Section B contains seven questions of two marks each, Section C contains five questions of three marks each, section D contains three long questions of five marks each and Section E contains two case study-based questions of 4 marks each.
- There is no overall choice. However, an internal choice has been provided in section B, C, D and E. You have to attempt only one of the choices in such questions.
- Use of calculators is not allowed.
Section – A (18 Marks)
Question 1.
If current in two parallel wires is flowing in the same direction then, what will be the nature of force between them? [1]
(a) Repulsive
(b) Attractive
(c) Both (a) and (b)
(d) None of these
Question 2.
What will be ratio of radii of two nuclei of mass numbers A1 and A2? [1]
(a) \(\left(\frac{A_1}{A_2}\right)^{1 / 3}\)
(b) \(\left(\frac{A_2}{A_1}\right)^{1 / 3}\)
(c) \(\left(\frac{A_1}{A_2}\right)^{1 / 2}\)
(d) \(\left(\frac{A_2}{A_1}\right)^{1 / 2}\)
Question 3.
A nucleus of mass number A has mass defect Am. What is the formula for the binding energy per nucleon of this nucleus? [1]
(a) \(\frac{\Delta m c^2}{\mathrm{~A}}\)
(b) \(\frac{\Delta m^2 c}{A}\)
(c) \(\frac{\Delta \mathrm{mc}}{\mathrm{A}}\)
(d) \(\frac{\mathrm{mc}^2}{\mathrm{~A}}\)
Question 4.
The SI unit of magnetic permeability of free space is: [1]
(a) TAm
(b) TA-1m
(c) T-1A-1m
(d) AT-1m
Question 5.
The given semiconductor, at room temperature, will have …………………. for conduction. [1]
(a) electrons
(b) holes
(c) Both electrons and holes
(d) None of these
Question 6.
Under which of the given condition does a junction diode works as an open switch. [1]
(a) Forward biased
(b) Reverse biased
(c) Both (a) and (b)
(d) None of these
Question 7.
Name the property by virtue of which a material opposes the flow of current through it. [1]
(a) Conductance
(b) Inductance
(c) Capacitance
(d) Resistance
Question 8.
Which one of these particles has the largest de-Broglie wavelength, if they have same kinetic energy? [1]
(a) neutron
(b) a-particle
(c) electron
(d) proton
Question 9.
What is the diameter of hydrogen atom? [1]
(a) 1.86 Å
(b) 1.46 Å
(c) 1.06 Å
(d) 1.56 Å
Questions 10.
What is the unit of power of a lens? [1]
(a) meter
(b) dioptre
(c) centimeter
(d) meter-1
Question 11.
According to the Bohr’s postulate of quantization of angular momentum for an orbiting electron in a hydrogen atom, which one of the following is correct: [1]
(a) mvr = \(\frac{n^2 h}{2 \pi}\)
(b) mvr = \(\frac{n h^2}{2 \pi}\)
(c) mvr = \(\frac{n h}{2 \pi}\)
(d) mvr = \(\frac{n^2 h^2}{2 \pi}\)
Question 12.
Consider two ideaLised systems: [1]
Case: (i) a parallel plate capacitor with big plates and littte spacing, and
Case : (ii) a Long soLenoid with Length L, R, and cross-sectional radius.
In (i) E is idealised as a constant between plates with a value of zero outside.
In (ii) the magnetic field is constant inside the solenoid and zero outside.
However, these idealised assumptions violate fundamental laws, as seen below:
(a) Case (i) contradicts Gauss’s law for electrostatic fields.
(b) Case (ii) contradicts Gauss’s law for magnetic fields.
(c) Case (i) agrees with \(\oint_s \text { E.dt }\) = 0
(d) Case (ii) agrees with \(\oint \text { H.dl }\) = 0
Question 13.
In given rectifier, wave rectification, what is the output frequency, if the input frequency is 50 Hz? [1]
(a) 25 Hz
(b) 50 Hz
(c) 75 Hz
(d) 100 Hz
Question 14.
An electron is having kinetic energy of 120 eV. What is the momentum? [1]
(a) 3.91 × 10-24 Kg m/sec
(b) 5.91 × 10-24 Kg m/sec
(c) 6.91 × 10-24 Kg m/sec
(d) 4.91 × 10-24 Kg m/sec
Question 15.
What is the de Broglie wavelength for a bullet of mass 0.040 kg travelling at the speed of 10 km/s? [1]
(a) 1.65 × 10-25 m
(b) 2.65 × 10-35 m
(c) 1.65 × 10-35 m
(d) 2.65 × 10-25 m
Two statements are given-one labelled Assertion (A) and the- other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true and R is NOT the correct explanation of A.
(c) A is true but R is false.
(d) A is false and R is also false.
Question 16.
Assertion (A): The photoelectric effect indicates light’s wave nature. [1]
Reason (R): The number of photons is proportional to light frequency.
Question 17.
Assertion (A): If the galvanometer and voltage source are switched in a balanced condition, the balanced condition remains the same. [1]
Reason (R): The balanced state of the Wheatstone bridge is independent of the resistance values.
Question 18.
Assertion (A): The Coulomb force Is the strongest force in the universe. [1]
Reason (R): Nuclear forces are weaker than Coulomb force.
Section – B (14 Marks)
Question 19.
A magnetised needle in a uniform magnetic field experiences a torque but no net force. An iron nail near a bar magnet however experiences a force of attraction in addition to torque. Why? [2]
Question 20.
Why electromagnetic waves are produced by a charged particle which is oscillating at a certain frequency? Sketch a schematic diagram depicting electric and magnetic fields as well. [2]
OR
When an ideal capacitor is charged by a dc battery, no current flows. However, when an alternating source is used, the current flows continuously. Justify.
Question 21.
How does the conductivity of a semiconductor vary with temperature? [2]
Question 22.
The wavelength ‘λ’ of a photon and the de Broglie wavelength of an electron have the same value. Show that the energy of photon is \(\frac{2 \lambda m c}{h}\) times the kinetic energy of electron. Where, c and h have their usual meanings. [2]
Question 23.
Explain the reason as to why equipotential surfaces are closer together in the regions of strong field and farther apart in the regions of weak field. [2]
OR
What is the reason for electric field being zero in the cavity of a hollow charged conductor?
Question 24.
Why do stable nuclei never have more protons than neutrons? [2]
Question 25.
How and why does the thickness of the depletion layer in a p-n junction diode vary with increase in reverse bias? [2]
Section – C (15 Marks)
Question 26.
Calculate the value of the e.m.f induced in a circular wire which is 88 cm long bent into a loop, placed perpendicular to a magnetic field of flux density 2.5 Wbm-2 if the loop is changed into 22 cm square and flux density is increased to 3.0 Wbm-2, within 0.5 sec. [3]
OR
A conducting rod of length l with one end pivoted is rotated with a uniform angular speed ω in a vertical plane, normal to a uniform magnetic field B. Find the expression for the e.m.f induced in this rod.
Question 27.
Consider a two slit interference arrangements such that the distance of the screen from the slits is half the distance between the slits. Obtain the value of D in terms of λ such that the first minima on the screen falls at a distance D from the centre O [3]
OR
In a Young’s double slit experiment , the two slits are 0.03 cm apart and the screen is placed 1.5 m away. The distance between the central bright fringe and the fourth bright fringe is measured to be 1 cm. Find the wavelength of light used.
Question 28.
The refractive indices of the material of the prism for red, green and blue wavelengths are 1.39, 1.44 and 1.47 respectively. Trace the paths of three rays and check which of the three colours will emerge out of face ‘AC’? Show diagrammatically.
Question 29.
The earth’s surface has a negative surface charge density of 10-9 cm-2. The potential difference of 400 kV between the top of the atmosphere and the surface results (due to the low conductivity of the lower atmosphere) in a current of only 1800 amp. over the entire globe.
If there were no mechanism of sustaining atmospheric electric field. How much time (roughly) would be required to neutralize the earth’s surface? (This never happens in practice because there is a mechanism to replenish electric charges, namely the continual thunderstorms and lightning in different part of the globe).
[Radius of earth = 6.37 × 106 m] [3]
Question 30.
A parallel plate capacitor ¡s charged by a battery. After sometime the battery is disconnected and a dielectric stab with Its thickness equal to the plate separation ¡s inserted between the plates. [3]
How will:
(A) the capacitance of the capacitor,
(B) potential difference between the plates and
(C) the energy stored in the capacitor be affected? Justify your answer in each case.
Section – D (15 Marks)
Question 31.
By using the Huygens’ wave theory of light, how can you prove the laws of reflection and refraction? Show with the help of suitable diagrams. [5]
OR
What is meant by wave front? Discuss the behavior of the following when a plane wave front is incident on each of them:
(A) Prism
(B) Concave mirror
(C) Convex lens
Question 32.
(A) An alternating e.m.f. is applied to a series combination of a resistor and capacitor. Derive an expression for the impedance of the circuit with the help of phasor diagram. [5]
(B) A series circuit has a resistor of 20Ω, an ammeter of negligible resistance and a capacitor. A source of 220V-50 Hz is connected with it. Calculate the reactance of the capacitor if the reading of ammeter is 2.5 ampere.
OR
(A) An alternating e.m.f. is applied to a series combination of a resistor and inductor. Derive an expression for the impedance of the circuit with the help of phasor diagram.
(B) A bulb of resistance 10Q is connected in series with an inductor of unknown inductance. The alternating source is marked 100 V, 50 Hz. Calculate the value of inductance if the phase angle between the voltage and current is \(\frac{\pi}{4}\) radian.
Question 33.
What do you understand by dipole moment of an electric dipole? Show mathematically that electric field intensity due to a short dipole at a distance V is along its axis and is inversely proportional to r3 for larger distances. [5]
OR
Answer the following questions in brief:
(A) Is it possible for two like charges to attract each other? If yes, how?
(B) Will a charged particle always move in the direction of electric field if free to move? Justify.
(C) What is the reason that electric field lines do not form closed loops?
(D) How can a uniform electric field be represented with the help of lines of force?
(E) What does q1 + q2 = 0 signify in electrostatics?
Section – D (8 Marks)
Question 34.
Optical Fibers: Optical fibers are flexible, transparent fibers made by drawing glass silica or plastic to a diameter slightly thicker than that of a human hair. Optical fibers are most commonly used as a means to transmit light between the two ends of the fiber and find wide usage in fiber-optic communications, where they permit transmission over longer distances and at higher data transfer rates than electrical cables Fibers are used instead of metal wires because signals travel along them with less loss; in addition, fibers are immune to electromagnetic interference, a problem from which metal wires suffer.Fibers are also used for illumination and imaging, and are often wrapped in bundles so they may be used to carry light into, or images out of confined spaces, as in the case of a fiberscope. Specially
(A) Give the name of principle of working of optical fibre. [1]
(B) What is the order of the thickness of strands of optical fibers? [1]
(C) What is the name of the inner part of optical fiber where light is restricted?
OR
In long distance communications, what is the most common name of optical fibers? [2]
Question 35.
Induction Cooking: Induction cooking is performed using direct induction heating of cooking vessels, rather than relying on indirect radiation, convection, or thermal
conduction. Induction cooking allows high power and rapid increases in temperature to be achieved, and changes in heat settings are instantaneous. In an induction cooktop or “induction stove”, a coil of copper wire is placed under the cooking vessel and designed fibers are also used for a variety of other applications, some of them being fiber optic sensors and fiber lasers.
an alternating electric current is passed through it. The resulting oscillating magnetic field wirelessly induces an electrical current in the vessel. This large eddy current flowing through the resistance of the vessel results in heating.
(A) Give name of the principle which used in Induction furnaces? [1]
(B) Give name the principle of transformers. [1]
(C) The number of primary and secondary turns in a transformer is 140 and 280 respectively. What is the value of current in secondary if current in primary turn is 4 A?
OR
Magnitude of e.m.f induced in a coil , when a magnet is inserted into it, how it upon resistance of coil? [2]