Practice Questions

Q13. The figure gives experimentally measured B vs. H variation in a ferromagnetic material. The retentivity, coercivity and saturation, respectively, of the material are: JEE Main 2020 (07 Jan Shift 2) JEE Main Previous Year Paper (1) 1.5T, 50A/m and 1.0T (2) 1.5T, 50A/m and 1.0T (3) 150A/m, 1.0T and 1.5T (4) 1.0T, 50A/m and 1.5T → ˆi+ˆj

Q13.An electron gun is placed inside a long solenoid of radius R on its axis. The solenoid has n turns/length and carries a current I. The electron gun shoots an electron along the radius of the solenoid with speed v. If the electron does not hit the surface of the solenoid, maximum possible value of v is (all symbols have their standard meaning): (1) eμ0nIR (2) eμ0nIR m 2m (3) eμ0nIR (4) 2eμ0nIR 4m m

Q13.A small bar magnet is placed with its axis at 30o with an external magnetic field of 0. 06 T experiences a torque of 0. 018 Nm. The minimum work required to rotate it from its stable to unstable equilibrium position is: (1) 6. 4 × 10−2 J (2) 9. 2 × 10−3 J (3) 7. 2 × 10−2 J (4) 11. 7 × 10−3 J

Q14.Proton with kinetic energy of 1 MeV moves from south to north. It gets an acceleration of 1012 m/s2 by an applied magnetic field (west to east). The value of magnetic field: (Rest mass of proton is 1.6 × 10−27kg ) (1) 0.71mT (2) 7.1mT (3) 0.071mT (4) 71mT

Q14.A long, straight Wire of radius a carries a current distributed uniformly over its cross-section. The ratio of the magnetic fields due to the wire at distance a and 2a , respectively from the axis of the wire is: 3 (1) 2 (2) 2 3 (3) 1 (4) 3 2 2 −

Q14.A very long wire ABDMNDC is shown in figure carrying current I. AB and BC parts are straight, long and at right angle. At D wire forms a circular turn DMND of radius R. AB, BC parts are tangential to circular turn at JEE Main 2020 (08 Jan Shift 2) JEE Main Previous Year Paper N and D. Magnetic filed at the center of circle is: (1) + − 2πR μ0I (π 1 ) (2) 2πRμ0I (π 1 ) √2 √2 μ0I (3) 2πR (π + 1) (4) μ0I2R

Q14.The electric field of a plane electromagnetic wave is given by E = E0 cos(kz + ωt) . At t = 0 , a positively √2 charged particle is at the point (x, y, z) = (0, 0, πk ) . If its instantaneous velocity at (t = 0) is v0ˆk , the force acting on it due to the wave is: (1) parallel to ˆi+ˆj (2) zero √2 (3) antiparallel to ˆi+ˆj (4) parallel to ˆk √2

Q14.A small point mass carrying some positive charge on it, is released from the edge of a table. There is a uniform electric field in this region in the horizontal direction. Which of the following options then correctly describe the trajectory of the mass ? (Curves are drawn schematically and are not to scale) (1) (2) (3) (4)

Q14.A paramagnetic sample shows a net magnetisation of 6 A/m when it is placed in an external magnetic field of 0. 4 T at a temperature of 4 K . When the sample is placed in an external magnetic field of 0. 3 T at a temperature of 24 K , then the magnetisation will be : (1) 1 A/m (2) 4 A/m (3) 2. 25 A/m (4) 0. 75 A/m

Q14.A galvanometer of resistance G is converted into a voltameter of range 0 −1 V by connecting a resistance R in series with it. The additional resistance that should be connected in series with R1 to increase the range of the voltmeter to 0 −2V will be : (1) G (2) R1 (3) R1 −G (4) R1 + G

Q14.A charged particle (mass m and charge q) moves along X axis with velocity V0 . When it passes through the → origin it enters a region having uniform electric field E = −Eˆj which extends upto x = d. Equation of path of electron in the region x > d is: qEd qEd (1) y = (x −d) (2) y = ( d2 −x) mv2 mv2 0 0 qEd (3) y = (4) y = qEd2 x mv2 0 mv20

Q14.A wire A , bent in the shape of an arc of a circle, carrying a current of 2 A and having radius 2 cm and another wire B, also bent in the shape of an arc of a circle, carrying a current of 3 A and having radius of 4 cm , are placed as shown in the figure. The ratio of the magnetic fields due to the wires A and B at the common centre O is: (1) 4 : 6 (2) 6 : 4 (3) 2 : 5 (4) 6 : 5

Q14.An AC circuit has R = 100Ω, C = 2μF and L = 80 mH, connected in series. The quality factor of the circuit is : (1) 2 (2) 0.5 (3) 20 (4) 400

Q14.In LC circuit the inductance L = 40 mH and capacitance C = 100 μF. If a voltage V (t) = 10sin(314t) is applied to the circuit, the current in the circuit is given as: (1) 0.52 cos(314t) (2) 10 cos(314t) (3) 5.2 cos(314t) (4) 0.52 sin(314t)

Q14.In the circuit, given in the figure currents in different branches and value of one resistor are shown. Then potential at point B with respect to the point A is: (1) +2V (2) −2V (3) –1V (4) +1V

Q15.An electrical power line, having a total resistance of 2Ω, delivers 1 kW at 220 V. The efficiency of the transmission line is approximately : (1) 72% (2) 91% (3) 85% (4) 96%

Q15.A charged particle going around in a circle can be considered to be a current loop. A particle of a mass m → carrying charge q is moving in a plane with speed v under the influence of magnetic field B. The magnetic moment of this moving particle is : B (1) mv2→ B (2) −mv2→ 2B2 2πB2 B (3) −mv2→ B (4) −mv2→ B2 2B2

Q15.If the magnetic field in a plane electromagnetic wave is given by → B = 3 × 10−8 sin(1.6 × 103x + 48 × 1010t)ˆjT, then what will be expression for electric field ? → → (1) V (2) V E = E = (60 sin(1.6 × 103x + 48 × 1010t)ˆk m ) (9 sin(1.6 × 103x + 48 × 1010t)ˆk m ) (3) → V (4) → V E = E = (3 × 10−8 sin(1.6 × 103x + 48 × 1010t)ˆj m ) (3 × 10−8 sin(1.6 × 103x + 48 × 1010t)ˆi m )

Q15.A planar loop of wire rotates in a uniform magnetic field. Initially, at t = 0 , the plane of the loop is perpendicular to the magnetic field. If it rotates with a period of 10s about an axis in its plane then the magnitude of induced emf will be maximum and minimum, respectively at: (1) 2.5 s and 7.5 s (2) 2.5 s and 5.0 s (3) 5.0 s and 7.5 s (4) 5.0 s and 10. 0 s

Q15.At time t = 0 magnetic field of 1000 Gauss is passing perpendicularly through the area defined by the closed loop shown in the figure. If the magnetic field reduces linearly to 500 Gauss, in the next 5s, then induced JEE Main 2020 (08 Jan Shift 1) JEE Main Previous Year Paper EMF in the loop is: (1) 56μV (2) 28μV (3) 48μV (4) 36μV

Q15. As shown in the figure, a battery of emf ∈ is connected to an inductor L and resistance R in series. The switch is closed at t = 0. The total charge that flows from the battery, between t = 0 and t = tc ( tc is the time constant of the circuit) is: (1) ∈L (2) ∈L eR2 R2 (1 −1e ) (3) ∈L (4) ∈R R2 eL2

Q15.Two identical capacitors A and B, charged to the same potential 5V are connected in two different circuits as shown below at time t = 0. If the charge on capacitors A and B at time t = CR is QA and QB respectively, then (Here e is the base of natural logarithm) (1) QA = VeC , QB = CV2 (2) QA = V C, QB = CV (3) QA = V C, QB = VeC (4) QA = CV2 , QB = VeC

Q15.An inductance coil has a reactance of 100 Ω . When an AC signal of frequency 1000 Hz is applied to the coil, the applied voltage leads the current by 45°. The self-inductance of the coil is (1) 1. 1 × 10−2 H (2) 1. 1 × 10−1 H (3) 5. 5 × 10−5 H (4) 6. 7 × 10−7 H JEE Main 2020 (02 Sep Shift 2) JEE Main Previous Year Paper

Q15.The magnetic field of a plane electromagnetic wave is B = 3 × 10−8 sin[200π(y + ct)]ˆi T . Where, c = 3 × 108 m s−1 is the speed of light the corresponding electric filed is : → → (1) (2) E = 9 + V/m E = −10−6 + V/m sin[200π(y ct)ˆk sin[200π(y ct)ˆk (3) → (4) → E = 3 × 10−8 + V/m E = −9 + V/m sin[200π(y ct)ˆk sin[200π(y ct)ˆk

Q15.A small bar magnet is moved through a coil at constant speed from one end to the other. Which of the following series of observations will be seen on the galvanometer G attached across the coil? Three positions shown describe: (a) the magnet's entry (b) magnet is completely inside and (c) magnet's exit. JEE Main 2020 (04 Sep Shift 1) JEE Main Previous Year Paper (1) (2) (3) (4)