Practice Questions

Q20.In the figure shown, what is the current (in Ampere) drawn from the battery? You are given: 𝑅1 = 15 Ω , 𝑅2 = 10 Ω , 𝑅3 = 20 Ω , 𝑅4 = 5 Ω, 𝑅5 = 25 Ω, 𝑅6 = 30 Ω, 𝐸= 15 V (1) 9 / 32 (2) 7 / 18 (3) 13 / 24 (4) 20 / 3

Q20.A resistance is shown in the figure. Its value and tolerance are given respectively by: (1) 27 𝑘Ω, 10% (2) 270 Ω, 5% (3) 270 Ω, 10% (4) 27 𝑘Ω, 20%

Q20.A 10 m long horizontal wire extends from North East to South West. It is falling with a speed of 5.0 m s−1, at right angles to the horizontal component of the earth's magnetic field of 0.3 × 10−4 Wb m−2. The value of the induced emf in the wire is: (1) 0.3 × 10−3 V (2) 1.1 × 10−3 V (3) 2.5 × 10−3 V (4) 1.5 × 10−3 V

Q20.Find the magnetic field at point P due to a straight line segment AB of length 6 cm carrying a current of 5 A. (See figure) (μ0 = 4π × 10−7 NA−2) (1) 1.5 × 10−5 T (2) 2.0 × 10−5 T (3) 3.0 × 10−5 T (4) 2.5 × 10−5 T

Q20.A magnet of total magnetic moment 10−2 ˆi A m2 is placed in a time varying magnetic field, Bˆi(cos ωt) where B = 1 Tesla and ω = 0.125 rad s−1 . The work done for reversing the direction of the magnetic moment at JEE Main 2019 (10 Jan Shift 1) JEE Main Previous Year Paper t = 1 second, is: (1) 0.007 J (2) 0.02 J (3) 0.014 J (4) 0.01 J

Q20.Two coils 'P' and 'Q' are separated by some distance. When a current of 3 A flows through coil 'P', a magnetic flux of 10−3 Wb passes through 'Q'. No current is passed through 'Q'. When no current passes through 'P' and a current of 2 A passes through 'Q', the flux through 'P' is: (1) 3.67 × 10−3 Wb (2) 6.67 × 10−4 Wb (3) 3.67 × 10−4 Wb (4) 6.67 × 10−3 Wb

Q20.There are two long co-axial solenoids of same length l. The inner and outer coils have radii r1 and r2 and number of turns per unit length n1 and n2 , respectively. The ratio of mutual inductance to the self-inductance of the inner-coil is : (1) n1 (2) n2 ⋅r1 n2 n1 r2 n2 (3) n2 2 (4) ⋅r2 n1 n1 r21

Q20.A proton, an electron, and a Helium nucleus, have the same energy. They are in circular orbits in a plane due to magnetic field perpendicular to the plane. Let rp, re and rHe be their respective radii, then, (1) re > rp = rHe (2) re < rp = rHe (3) re < rp < rHe (4) re > rp > rHe

Q20.The region between y = 0 and y = d contains a magnetic field B = B^z. A particle of mass m and charge q mv , the acceleration of the charged particle at the point of its enters the region with a velocity →v = v^i. if d = 2qB emergence at the other side is : (1) qv m B ( 12^i −√32 ^j) (2) qvmB ( √32 ^i + 12 ^j) (3) qv B −^j+^i (4) None of the above m ( √2 )

Q20.One of the two identical conducting wires of length L is bent in the form of a circular loop and the other one into a circular coil of N identical turns. If the same current is passed in both, the ratio of the magnetic field at the centre of the loop (BL) to that at the centre of the coil (BC), i.e. BL will be BC 1 (1) 2 (2) N1 N (3) N (4) N 2

Q20.As shown in the figure, two infinitely long, identical wires are bent by 90o and placed in such a way that the segments LP and QM are along the x - axis, while segments PS and QN are parallel to the y - axis. If OP = OQ = 4cm, and the magnitude of the magnetic field at O is 10−4 T, and the two wires carry equal currents (see figure), the magnitude of the current in each wire and the direction of the magnetic field at O will be (μ0 = 4π × 10−7NA−2) : (1) 20 A, perpendicular into the page (2) 20 A, perpendicular out of the page (3) 40 A, perpendicualr into the page (4) 40 A, perpendicular out of the page JEE Main 2019 (12 Jan Shift 1) JEE Main Previous Year Paper

Q20.A thin strip 10 cm long is on a U shaped wire of negligible resistance and it is connected to a spring of spring constant 0.5 N m-1 (see figure). The assembly is kept in a uniform magnetic field of 0.1 T . If the strip is pulled from its equilibrium position and released, the number of oscillations it performs before its amplitude decreases by a factor of e is N . If the mass of the strip is 50 grams, its resistance 10Ω and air drag negligible, JEE Main 2019 (08 Apr Shift 1) JEE Main Previous Year Paper N will be close to: (1) 1000 (2) 5000 (3) 10000 (4) 50000

Q20.A moving coil galvanometer has resistance 50 Ω and it indicates full deflection at 4 mA current. A voltmeter is made using this galvanometer and a 5 kΩ resistance. The maximum voltage, that can be measured using this voltmeter, will be close to: (1) 40 V (2) 15 V (3) 20 V (4) 10 V

Q21.A thin ring of 10 cm radius carries a uniformly distributed charge. The ring rotates at a constant angular speed of 40π rads-1 about its axis, perpendicular to its plane. Is the magnetic field its centre is 3.8 × 10-9T , then the charge carried by the ring is close to μ0 = 4π × 10-7N / A2 . (1) 4 × 10-5 C (2) 3 × 10-5 C (3) 2 × 10-6 C (4) 7 × 10-6 C

Q21.An insulating thin rod of length l has a linear charge density ρ(x) = ρ0 xl on it. The rod is rotated about an axis passing through the origin (x = 0) and perpendicular to the rod. If the rod makes n rotations per second, then the time averaged magnetic moment of the rod is: (1) π n ρ0l3 (2) n ρ0l3 4 (3) π n ρ0 l3 (4) π3 n ρ0l3

Q21.A particle of mass m and charge q is in an electric and magnetic field given by → → E = 2^i + 3^j; B = 4^j + 6^k The charged particle is shifted from the origin to the point P(x = 1; y = 1) along a straight path. The magnitude of the total work done is : (1) (0.35)q (2) 5q (3) (2.5) q (4) (0.15)q

Q21.A square loop is carrying a steady current I and the magnitude of its magnetic dipole moment is m . If this square loop is changed to a circular loop and it carries the same current, the magnitude of the magnetic dipole moment of circular loop will be: JEE Main 2019 (10 Apr Shift 2) JEE Main Previous Year Paper 4m 3m (1) (2) π π (3) 2m (4) m π π

Q21.A current of 2 mA was passed through an unknown resistor which dissipated a power of 4.4 W. Dissipated power when an ideal power supply of 11 V is connected across it is: (1) 11 × 105 W (2) 11 × 10−3 W (3) 11 × 10−5 W (4) 11 × 10−4 W

Q21.A power transmission line feeds input power at 2300 V to a step down transformer with its primary windings having 4000 turns. The output power is delivered at 230 V by the transformer. If the current in the primary of the transformer is 5 A and its efficiency is 90 % , the output current would be: (1) 35 A (2) 25 A (3) 50 A (4) 45 A

Q21.Two very long, straight, and insulated wires are kept at 90𝑜 angle from each other in xy - plane as shown in figure. These wires carry currents of equal magnitude I , whose direction are shown in the figure. The net magnetic field at point P will be: JEE Main 2019 (08 Apr Shift 2) JEE Main Previous Year Paper μ0I +μ0I (1) - 2πd ^x + ^y (2) πd ^z μ0I (3) ^x + ^y (4) Zero 2πd

Q21.Consider the LR circuit shown in the figure. If the switch S is closed at t = 0 then the amount of charge that passes through the battery between t = 0 and t = RL is: JEE Main 2019 (12 Apr Shift 2) JEE Main Previous Year Paper (1) 7.3 EL (2) EL R2 7.3R2 (3) 2.7 EL (4) EL R2 2.7R2

Q21. In the above circuit, C = √32 μF, R2 = 20 Ω, L = √310 H and R1 = 10 Ω. Current in L-R1 path is I1 and in C-R2 path it is I2. The voltage of AC source is given by, V = 200√2 sin (100 t) volts. The phase difference between I1 and I2 is: (1) 60o (2) 0o (3) 30o (4) 150o

Q21.A bar magnet is demagnetized by inserting it inside a solenoid of length 0.2 𝑚, 100 turns, and carrying a current of 5.2 𝐴. The coercivity of the bar magnet is: JEE Main 2019 (09 Jan Shift 1) JEE Main Previous Year Paper (1) 285 𝐴/ 𝑚 (2) 2600 𝐴/ 𝑚 (3) 520 𝐴/ 𝑚 (4) 1200 𝐴/ 𝑚

Q21.A moving coil galvanometer has a coil with 175 turns and area 1 cm2. It uses a torsion band of torsion constant 10−6 N m/rad The coil is placed in a magnetic field B parallel to its plane. The coil deflects by 1o for a current of 1 mA The value of B (in tesla) is approximately: (1) 10−2 (2) 10−4 (3) 10−3 (4) 10−1

Q21.A 20 H inductor coil is connected to a 10 Ω resistance in series as shown in figure. The time at which rate of dissipation of energy (Joule's heat) across resistance is equal to the rate at which magnetic energy is stored in the inductor, is: (1) 1 (2) 2ln2 (3) 2 (4) ln2 2ln2 ln2