NBSE Question Papers Physics Term-1 (Set-1) for Class 12

Class 12  SET-1 Series NBSE/XII/2021 TERM-I Code No. 042/12/1 Roll No.  Candidates must write the Code No. on the title page of the OMR sheet. l Please check that this question paper contains 12 pages. l Code number given on the right hand side of the question paper should be written on the title page of the OMR sheet. l Please check that this question paper contains 55 questions. l 15 minutes time has been allotted to read this question paper. PHYSICS Time Allowed : 90 Minutes Maximum Marks : 35 General Instructions: 1. The Question Paper contains three sections. 2. Section A has 25 questions. Attempt any 20 questions. 3. Section B has 24 questions. Attempt any 20 questions. 4. Section C has 6 questions. Attempt any 5 questions. 5. All questions carry equal marks. 6. There is no negative marking. NBSE 2021 1 [P.T.O.

SECTION A This section consists of 25 multiple choice questions with overall choice to attempt any 20 questions. In case more than desirable number of questions are attempted, ONLY first 20 will be considered for evaluation. 1. Equipotential surfaces (a) are closer in regions of large electric fields compared to regions of lower electric fields. (b) will be more crowded near sharp edges of a conductor. (c) will be more crowded near regions of large charge densities. (d) all of the above 2. A charge Q is uniformly distributed over the surface of a spherical shell of radius R. The work done in bringing a test charge Q0 from its centre to its surface is (a) 1 QQ0 (b) 1 QQ0 4πε0 R 4πε0 2R (c) QQ0 (d) zero ε0R 3. A dipole is placed parallel to electric field. If W is the work done in rotating the dipole from 0° to 60°, then work done in rotating it from 0° to 180° is (a) 2 W (b) 3 W (c) 4 W (d) W 2 4. Three capacitors of capacitances 1µF, 2 µF and 3 µF are connected in series and a potential difference of 11 V is applied across the combination, then the potential difference across the plates of 1µF capacitor is C1 C2 C3 +q –q +q –q +q –q V (a) 2V (b) 3V (c) 4V (d) 6V 5. The capacitance of a capacitor becomes 8 times its original value if a dielectric slab of thickness 9 t = 1 d is introduced in between the plates, where d is the separation between the plates. The 3 dielectric constant of the slab is (a) 14 (b) 11 (c) 8 (d) 11 11 14 11 8 6. The electric flux through a closed Gaussian surface depends upon (a) net charge enclosed and permittivity of the medium NBSE 2021 2

(b) net charge enclosed, permittivity of the medium and the size of the Gaussian surface (c) net charge enclosed only (d) permittivity of the medium only 7. A parallel plate capacitor is charged by a battery. Once it is charged, the battery is removed. Now a dielectric material is inserted between the plates of the capacitor, which of the following does not change? (a) Electric field between the plates (b) Potential difference across the plates (c) Charge on the plates (d) Energy stored in the capacitor 8. Two cells of emf’s approximately 5 V and 10 V are to be accurately compared using a potentiometer of length 400 cm. (a) The battery that runs the potentiometer should have voltage of 8 V. (b) The battery of potentiometer can have a voltage of 15 V and resistance R adjusted so that the potential drop across the wire slightly exceeds 10 V. (c) The first portion of 50 cm of wire itself should have a potential drop of 10 V. (d) Potentiometer is usually used for comparing resistances and not voltages. 9. A metal rod of length 10 cm and a rectangular cross-section of 1 cm × 1 cm is connected to a battery across opposite faces. The resistance will be 2 (a) maximum when the battery is connected across 1 cm × 1 cm faces. 2 (b) maximum when the battery is connected across 10 cm × 1 cm faces. (c) maximum when the battery is connected across 10 cm × 1 cm faces. 2 (d) same irrespective of the three faces. 10. Kirchhoff’s junction rule is a reflection of (a) conservation of current density vector. (b) conservation of charge. (c) the fact that there is no accumulation of charge at a junction (d) Both (b) and (c) 11. Which of the following characteristics of electrons determines the current in a conductor? (a) Drift velocity alone (b) Thermal velocity alone (c) Both drift velocity and thermal velocity (d) Neither drift nor thermal velocity. 12. A 5°C rise in temperature is observed in a conductor by passing a current. If the current is doubled, the rise in temperature of the conductor will be nearly (a) 10°C (b) 20°C (c) 40°C (d) 2.5°C 13. If the ratio of concentration of electrons to that of hole in a semiconductor is 7 and the ratio of 5 currents is 7 , then what is the ratio of their drift velocities? 4 (a) 5 (b) 4 (c) 5 (d) 4 85 47 NBSE 2021 3 [P.T.O.

14. In the circuit diagram the electric current through branch BC is AB 3A H 2A CD F 5A 3A G E (a) 1A (b) 2A (c) 4A (d) 5A 15. The SI unit of magnetic flux density is (a) Weber (b) Tesla (c) Maxwell (d) Gauss 16. Current sensitivity of a galvanometer can be increased by decreasing (a) torsional constant K (b) area A (c) magnetic field B (d) number of turns N 1 7. A circular coil of radius a carries an electric current. The magnetic field due to the coil at a point on the axis of the coil located at a distance r from centre of the coil, such that r >> a varies (a) 1 (b) 1 (c) 1 (d) 1 r3 r2 r 3 r2 1 8. If the horizontal and vertical components of earth’s magnetic field are equal at a certain place, the angle of dip is (a) 90° (b) 60° (c) 45° (d) 0° 19. The angle between the magnetic meridian and the geographical meridian is known as (a) Magnetic dip (b) Magnetic declination (c) Magnetic moment (d) Magnetic field strength 20. Two coils of self inductances 2mH and 8mH are placed to close to each other that the flux linkage is complete between the coils. The mutual inductance between these coils is: (a) 4mH (b) 6mH (c) 10mH (d) 16mH 21. An electron moves on a straight line path XY as shown. The abcd is a coil adjacent to the path of electron. What will be the direction of current, if any, induced in the coil? a bd c X electron Y NBSE 2021 4

(a) The current will reverse its direction as the electron goes past the coil. (b) No current induced (c) abcd (d) adcb 22. Magnetic flux through a coil changes from 0.7 Wb to 0.2 Wb in 0.1 second. The induced emf developed in the coil is (a) 7V (b) 5V (c) 20V (d) 2V 2 3. The variation of induced emf (E) with time t in a coil if a short bar magnet is moved along its axis with a constant velocity is best represented as S  N EE O t O t (a) (b) E E O t O t (c) (d) (a) a (b) b (c) c (d) d 2 4. When 100 volt dc is applied across a solenoid, a current of 1.0 A flows in it. When 100 volt ac is applied across the same coil, the current drops to 0.5A. If the frequency of ac source is 50Hz, the impedance and inductance of solenoid are: (a) 200 ohm and 0.55 henry (b) 100 ohm and 0.86 henry (c) 200 ohm and 1.0 henry (d) 100 ohm and 0.93 henry 2 5. In an ac circuit the phase difference between current and emf is 45°. The circuit contains (a) A pure inductance (b) A pure resistance (c) A pure capacitance (d) A resistance, an inductance and a capacitance in series NBSE 2021 5 [P.T.O.

SECTION B This section consists of 24 multiple choice questions with overall choice to attempt any 20 questions. In case more than desirable number of questions are attempted, ONLY first 20 will be considered for evaluation. 2 6. An area A = 0.5m2 shown in the figure and is situated in a uniform magnetic field B = 4.0 Wb/m2 and its normal makes an angle of 60° with the field. The magnetic flux passing through the area A would be equal to B 60° (a) 2.0 Wb (b) 1.0 Wb (c) 3 Wb (d) 0.5Wb 2 7. If ∫ E ⋅ ds = 0 over a surface , then (a) The electric field inside the surface and on it is zero (b) All charges must necessarily be outside the surface (c) The number of flux lines entering the surface must be equal to the number of flux lines leaving it (d) Both (b) and (c) 2 8. Consider a region inside which there are various types of charges but the total charge is zero. At points outside the region (a) The electric field is necessarily zero (b) The electric field is due to the dipole moment of the charge distribution only (c) The work done to move a charged particle along a closed path , away from the region, will be zero. (d) None of these 29. The electrostatic potential on the surface of a charge conducting sphere is 100 V. Two statements are made in this regard: S1: At any point inside the sphere, electric intensity is zero. S2: At any point inside the sphere, the electrostatic potential is 100 V. Which of the following is a correct statement? (a) S1 is true but S2 is false (b) Both S1 and S2 are false NBSE 2021 6

(c) S1 is true, S2 is also true and S1 is the cause of S2 (d) S1 is true, S2 is also true but the statements are independent. 30. Three capacitors of capacitances 3 µF, 9 µF and 18 µF connected first in series and then in parallel. The ratio of equivalent capacitance in two cases (Cs/Cp) will be (a) 1:15 (b) 15:1 (c) 1:1 (d) 1:3 3 1. The core used in transformers and other electromagnetic devices are laminated (a) to increase the magnetic field (b) to increase the level of magnetic saturation of the core (c) to reduce the magnetism in the core (d) to reduce eddy current losses in the core 32. An alternating voltage of frequency w is induced in electric circuit consisting of an inductance L and capacitance C, connected in series. Then across the inductance coil (a) current is maximum when w2 = 1 (b) current is minimum when w2 = 1 LC LC (c) voltage is minimum when w2 = 1 (d) voltage is zero when w2 = 1 LC LC 33. Two identical thin rings, each of radius R metre are co-axially placed at distance R metre apart. If Q1 and Q2 coulomb are respectively the charges uniformly spread on the two rings, the work done in moving a charge q from the centre of one ring to that of the other is (a) Zero ( )(b) q(Q1 − Q2 ) 2 −1 2.4πε0R (c) q(Q1 − Q2 ) 2 ( )(d) q(Q1 − Q2 ) 2 +1 2.4πε0R 4πε0R 34. Two batteries of emf e1 and e2 (e2 > e1) and internal resistances r1 and r2 respectively are connected in parallel as shown in figure. e1 r1 A B e2 r2 (a) The equivalent emf eeq of the two cells is between e1 and e2 i.e. e1 < eeq < e2 (b) The equivalent emf eeq is smaller than e1 NBSE 2021 7 [P.T.O.

(c) The eeq is given by eeq = e1 + e2 always (d) eeq is independent of internal resistances r1 and r2 3 5. The value of current I3 is given by 20W I1 I1 l3 40W 40V I2 80V I2 20W (a) 0A (b) 0.5A (c) 1.6 A (d) 2 A 7 3 6. From the graph between current I and voltage V shown below, identify the portion corresponding to negative resistance E IB C AD V (a) AB (b) BC (c) CD (d) DE 3 7. The length of a potentiometer wire is 100 cm and the emf of the standard cell is E volt. It is employed to measure the emf of a battery of internal resistance 0.5 ohm. If the balance point is obtained at length 30 cm from the positive end, the emf of the battery is (i = current in potentiometer wire) (a) 30 E (b) 30 E (c) 30 (E − 0.5 i) (d) 30 E 100.5 100 − 0.5 100 100 38. The sensitivity of a moving coil galvanometer increases with the decrease in: (a) number of turns (b) area of coil (c) magnetic field (d) torsional rigidity 3 9. A rectangular loop carrying a current i is situated near a long straight wire such that the wire is parallel to one of the sides of the loop and is in the plane of the loop. If a steady current I is established in the wire, as shown in fig., the loop will i I NBSE 2021 8

(a) Rotate about an axis parallel to the wire (b) Move away from the wire (c) Move towards the wire (d) Remain stationary 40. A bar magnet AB with magnetic moment M is cut into two equal parts perpendicular to its axis. One part is kept over the other so that end B is exactly over A. What will be the magnetic moment of the combination so formed? (a) M (b) 3 M (c) M (d) Zero 44 41. A small piece of metal wire is dragged across the gap between the poles of a magnet in 0.4 s. If change in magnetic flux in the wire is 8 × 10–4 Wb, then emf induced in the wire is (a) 8 × 10–3 V (b) 6 × 10–3 V (c) 4 × 10–3 V (d) 2 × 10–3 V 42. Which of the following combinations should be selected for better tuning of an LCR circuit used for communication? (a) R = 20 ohm, L = 1.5 H, C = 35 µF (b) R = 25 ohm, L = 2.5 H, C = 45 µF (c) R = 15 ohm, L = 3.5 H, C = 30 µF (d) R = 25 ohm, L = 1.5 H, C = 45 µF 43. If the electric field is given by (6i + 3j + 4k) N/C, the flux through a surface of area 20 m2 in the Y-Z plane is (a) 12 Nm2 (b) 120 Nm2 (c) 360 Nm2 (d) 80 Nm2 CC CC 4 4. If the number of turns in a coil is doubled, then its self inductance becomes (a) Double (b) Half (c) Four times (d) Unchanged 4 5. Assertion(A): The capacitance of a parallel plate capacitor increases with decrease of distance between the plates. Reason(R): Capacitance of a parallel plate capacitor i.e. C is directly proportional to d. (a) Both assertion and reason are true and reason is the correct explanation of assertion. (b) Both assertion and reason are true and reason is not the correct explanation of assertion. (c) Assertion is true but reason is false (d) Assertion is false but reason is true 46. Assertion(A): The conductivity of an electrolyte is very low as compared to metal at room temperature. Reason(R): The number density of free ions in electrolyte is much smaller as compared to number density of free electrons in metals. Further, ions drift much more slowly, being heavier. (a) Both assertion and reason are true and reason is the correct explanation of assertion. (b) Both assertion and reason are true and reason is not the correct explanation of assertion. (c) Assertion is true but reason is false (d) Assertion is false but reason is true 4 7. Assertion(A): When radius of a circular loop carrying current is doubled, its magnetic moment becomes four times. NBSE 2021 9 [P.T.O.

Reason(R): Magnetic moment depends on area of the loop. (a) Both assertion and reason are true and reason is the correct explanation of assertion. (b) Both assertion and reason are true and reason is not the correct explanation of assertion. (c) Assertion is true but reason is false (d) Assertion is false but reason is true 4 8. Assertion(A): When a rod AB moves in a transverse magnetic field, an emf is induced in the rod; the end becomes magnetic with end A positive. Reason(R): A Lorentz force evB acts on free electrons, so electrons move from B to A, thus by making end A positive and end B negative. (a) Both assertion and reason are true and reason is the correct explanation of assertion. (b) Both assertion and reason are true and reason is not the correct explanation of assertion. (c) Assertion is true but reason is false (d) Assertion is false but reason is true 49. Assertion(A): If a proton and an a-particle enter a uniform magnetic field perpendicularly with the same speed, the time period of revolution of a-particle is double that of proton. Reason(R): In a magnetic field, the period of revolution of a charged particle is directly proportional to the mass of particle and is inversely proportional to charge of particle. (a) Both assertion and reason are true and reason is the correct explanation of assertion. (b) Both assertion and reason are true and reason is not the correct explanation of assertion. (c) Assertion is true but reason is false (d) Assertion is false but reason is true SECTION C This section consists of 6 multiple choice questions with an overall choice to attempt any 5. In case more than desirable number of questions are attempted, ONLY first 5 will be considered for evaluation. 5 0. A plane of surface area S is placed in an electric field such that the direction of normal on surface ‘S’ makes an angle ‘q’ with the direction of electric field E . The electric flux through the surface is E S (a) ES q n (b) ES sin q (c) ES cos q (d) Zero NBSE 2021 10

5 1. Two identical metallic plates are given positive charges Q1 and Q2 (Q2< Q1). If these plates are brought together to form a parallel plate capacitor, then potential difference between them will be (a) Q1 + Q2 (b) Q1 + Q2 (c) Q1 − Q2 (d) Q1 − Q2 2C C C 2C CASE STUDY Read the following paragraph and answers the questions. An LC circuit oscillating at its natural resonant frequency can store electrical energy. A capacitors store electrical energy in the electric field (E) between its plates, depending on the voltage across it, and an inductor stores magnetic energy in its magnetic field(B), depending on the current through it. If an inductor is connected across a charged capacitor, the voltage across the capacitor will drive a current through inductor, building up a magnetic field around it. The voltage across the capacitor falls to zero as the charge is used by the current flow. At this point, the energy stored in the coils magnetic field induces a voltage across the coil, because inductor oppose changes in current. This induced voltage cause a current to begin recharge the capacitor with a voltage of opposite polarity to its original charge. Due to Faraday’s law, the emf which drives the current is caused by a decrease in magnetic field, thus the energy required to charge the capacitor is extracted from the magnetic field. When the magnetic field is completely dissipated the current will stop; and the charge will again be stored in the capacitor with the opposite polarity as before. Then the cycle will begin again, with the current flowing in the opposite direction through the inductor. The charge flows back and forth between the plates of the capacitor, through the inductor. The energy oscillates back and forth between the capacitor and the inductor until internal resistance makes the oscillations die out. The tuned circuit’s action, known mathematically as harmonic oscillator, is similar to a pendulum swinging back and forth. ii –––– ++++ L CE L CE ++++ –––– 5 2. In an LC oscillator, the frequency of oscillator is …………. L or C. (a) directly proportional to (b) proportional to the square of (c) independent of the value of (d) inversely proportional to square root of NBSE 2021 11 [P.T.O.

53. An LC oscillator cannot be used to produce (a) high frequencies (b) audio frequencies (c) very low frequencies (d) very high frequencies 54. In an LC oscillator, if the value of L is increased four times, the frequency of oscillations is (a) increased by 2 times (b) decreased by 4 times (c) increased by 4 times (d) decreased by 2 times 5 5. In an ideal parallel LC circuit, the capacitor is charged by connecting it to a dc source, which is then disconnected. The current in the circuit (a) becomes zero instantly (b) grows monotonically (c) decays monotonically (d) oscillates instantly NBSE 2021 12