NBSE Question Papers Physics Term-1 (Set-3) for Class 12

Class 12  SET-3 Series NBSE/XII/2021 TERM-I Code No. 042/12/3 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. If a positive charge is displaced against the electric field in which it was situated, then (a) work will be done by the electric field on the charge. (b) the intensity of the electric field decreases. (c) energy of the system will decrease. (d) energy will be provided by external source displacing the charge. 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 & 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 stab 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 (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 NBSE 2021 2

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. A potentiometer wire is 100 cm long and a constant potential difference is maintained across it. Two cells are connected in series first to support one another and then in opposite direction. The balance points are obtained at 50 cm and 10 cm from the positive end of the wire in the two cases. The ratio of emf 's is (a) 3 : 4 (b) 3 : 2 (c) 5 : 1 (d) 5 : 4 9. A metal rod of length 10 cm and a rectangular cross-section of 1 cm × ½ cm is connected to a battery across opposite faces. The resistance will be (a) maximum when the battery is connected across 1 cm × ½ cm faces. (b) maximum when the battery is connected across 10 cm × 1 cm faces. (c) maximum when the battery is connected across 10 cm × ½ cm faces. (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 charged 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 8 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 D C F 5A 3A G E (a) 1A (b) 2A (c) 4A (d) 5A 1 5. If in a moving coil galvanometer, a current I in its coil produces a deflection θ,then (a) I ∝ tan θ (b) I ∝ θ2 (c) I ∝ θ (d) I ∝ θ 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 18. 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 2 0. Two coils of self inductances 2mH an 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 2 1. 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. Self inductance of a coil is the mechanical analogue of (a) Energy (b) Momentum (c) Inertia (d) Power 23. 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 25. 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. 26. 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. T he dimensional formula of electric flux is (b) [M–1 L3 T–3 A–1] (a) [M1 L1 T–2] (d) [M1 L–3 T3 A1] (c) [M2 L2 T–2 A–2] 28. 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 (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 NBSE 2021 6

31. 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 LC (b) current is minimum when w2 = 1 LC (c) voltage is minimum when w2 = 1 LC (d) voltage is zero when w2 = 1 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 3 4. 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 (c) The eeq is given by eeq = e1 + e2 always (d) eeq is independent of internal resistances r1 and r2 NBSE 2021 7 [P.T.O.

35. 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. A cell of emf(E) and internal resistance r is connected across a variable external resistance R. The graph of terminal potential difference V as a function of R is eee V V V V OR OR OR OR (a) (b) (c) (d) (a) a (b) b (c) c (d) d 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 39. 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 4 0. 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 44. The magnitude of induced emf in a coil depend on (a) the amount of magnetic flux linked by the coil. (b) the amount of electric flux linked by the coil. (c) the rate of change of magnetic flux linked by the coil. (d) the rate of change of electric flux linked by the coil. 45. 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. NBSE 2021 9 [P.T.O.

(c) Assertion is true but reason is false. (d) Assertion is false but reason is true. 47. Assertion(A): Magnetic moment of an atom is due to both, the orbital motion and spin motion of every electron. Reason(R): A charged particle produces a magnetic field. (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): When a magnetic dipole is placed in a non uniform magnetic field, only a torque acts on a dipole. Reason(R): Force would also act on dipole if magnetic field were non-uniform. (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 q (a) ES n (b) ES sin q (c) ES cos q (d) Zero NBSE 2021 10

51. W hich of the following statement is true for the given circuit? V1 = 30 V V2 = 20 V S1 + S3 + S2 C1 = 2 pF C2 = 3 pF (a) With S1 closed, V1 = 15 V, V2 = 20 V (b) With S3 closed, V1 = V2 = 25 V (c) With S1 and S2 closed, V1 = V2 = 0 (d) With S1 and S3 closed, V1 = 30V, V2 = 20 V CASE STUDY Read the following paragraph and answers the questions. Metal detectors are useful for finding metal inclusions hidden within objects, or metal objects buried underground. They often consist of a handheld unit with a sensor probe which can be swept over the ground or other objects. Another common type are stationary “walk through” metal detectors. At an airport, a person is made to walk through the doorway of a metal detector, for security reasons. If she/he is carrying anything made of metal, the metal detector emits a sound. When you walk through a metal detector, you are, in fact, walking through a coil of many turns. The coil is connected to a capacitor tuned so that the circuit is in resonance. When you walk through with metal in your pocket, the impedance of the circuit changes – resulting in significant change in current in the circuit. This change in current is detected and the electronic circuit causes a sound to be emitted as an alarm. 52. At resonance the impedance of the circuit is (a) Maximum (b) Minimum (c) Zero (d) Depends on the frequency of circuit 5 3. I n an AC circuit consisting of a coil and a bulb how will the brightness of the bulb change if the frequency of source is increased. (a) No changes (b) Increases (c) Decreases (d) First decreases then increases NBSE 2021 11 [P.T.O.

54. I n an ac circuit, the applied voltage and the current flowing are E =110 sin pt and I = 11 sin  πt + π respectively. What is the power consumed in the circuit?  3  (a) 0 (b) 605W (c) 302.5W (d) 1210W 5 5. The selectivity of a series LCR a.c. circuit is large, when (a) both L and R are large (b) both L and R are small (c) L is large and R is small (d) L is equal to R NBSE 2021 12