Practice Questions

Q21.In the figure shown, a circuit contains two identical resistors with resistance R = 5 Ω and an inductance with L = 2 mH. An ideal battery of 15V is connected in the circuit. What will be the current through the battery long after the switch is closed? (1) 5.5 A (2) 6 A (3) 3 A (4) 7.5 A

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 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.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 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.A transformer consisting of 300 turns in the primary and 150 turns in the secondary gives output power of 2.2 kW . If the current in the secondary coil is 10 A , then the input voltage and current in the primary coil are: (1) 440 V and 20 A (2) 220 V and 20 A (3) 440 V and 5 A (4) 220 V and 10 A JEE Main 2019 (10 Apr Shift 1) JEE Main Previous Year Paper

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.A rigid square loop of side ‘a’ and carrying current I2 is lying on a horizontal surface near a long current I1 carrying wire in the same plane as shown in figure. The net force on the loop due to the wire will be: (1) Attractive and equal to μ0I1I2 (2) Repulsive and equal to μ0I1I2 3π 4π μ0I1I2 (3) Repulsive and equal to (4) Zero 2π

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.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 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

Q22.A plane electromagnetic wave having a frequency f = 23.9 GHz propagates along the positive z− direction in free space. The peak value of the Electric Field is 60 V/m. Which among the following is the acceptable magnetic field component in the electromagnetic wave? → → (1) (2) B = 2 × 10−7 sin(0.5 × 103z −1.5 × 1011t)ˆi B = 2 × 10−7 sin(1.5 × 103x + 0.5 × 1011t)ˆj → → (3) (4) B = 2 × 107 sin(0.5 × 103z + 1.5 × 1011t)ˆi B = 60 sin(0.5 × 103x + 1.5 × 1011t)ˆi

Q22.The magnitude of the magnetic field at the centre of an equilateral triangular loop of side 1 m which is carrying a current of 10 A is: [Take μ0 = 4π × 10-7 N A-2 ] (1) 3 μT (2) 1 μT (3) 18 μT (4) 9 μT

Q22.A rectangular coil (Dimension 5 cm × 2.5 cm ) with 100 turns, carrying a current of 3 A in the clock-wise direction, is kept centered at the origin and in the X −Z plane. A magnetic field of 1 T is applied along X −axis . If the coil is tilted through 45° about Z −axis , then the torque on the coil is: (1) 0.42 N m (2) 0.55 N m (3) 0.38 N m (4) 0.27 N m

Q22.A solid metal cube of edge length 2 cm is moving in the positive y-direction, at a constant speed of 6 m s−1 . There is a uniform magnetic field of 0.1 T in the positive z-direction. The potential difference between the two faces of the cube, perpendicular to the x-axis, is (1) 12 mV (2) 1 mV (3) 2 mV (4) 6 mV

Q22.Given below in the left column are different modes of communication using the kinds of waves given in the right column. (1) Optical Fibre Communication (P) Ultrasound (2) Radar (Q) Infrared Light (3) Sonar (R) Microwaves (4) Mobile Phones (S) Radio Waves From the options given below, find the most appropriate match between entries in the left and the right column. (1) 1 −Q, 2 −S, 3 −P, 4 −R (2) 1 − S, 2 −Q, 3 −R, 4 −P (3) 1 −Q, 2 −S, 3 −R, 4 −P (4) 1 −R, 2 −P, 3 −S, 4 −Q

Q22.An alternating voltage 𝑉( 𝑡) = 220sin100𝜋𝑡 volt is applied to a purely resistive load of 50 Ω . The time taken for the current to rise from half of the peak value to the peak value is: (1) 7.21 ms (2) 5 . 25 ms (3) 2.24 ms (4) 3.33 ms

Q22.A current loop, having two circular arcs joined by two radial lines is shown in the figure. It carries a current of 10 𝐴. The magnetic field at point 𝑂 will be close to: (1) 1.5 × 10-7 𝑇 (2) 1.0 × 10-7 𝑇 (3) 1.5 × 10-5 𝑇 (4) 1.0 × 10-5 𝑇

Q22.A point source of light, S is placed at a distance L in front of the center of plane mirror of width d which is hanging vertically on a wall. A man walks in front of the mirror along a line parallel to the mirror, at a distance 2L as shown below. The distance over which the man can see the image of the light source in the mirror is: (1) 3d (2) 2d (3) d (4) d 2

Q22.A series AC circuit containing an inductor (20 mH), a capacitor (120 μF) and a resistor (60 Ω) is driven by an AC source of 24 V/50 Hz. The energy dissipated in the circuit in 60 s is: (1) 5.17 × 102 J (2) 3.39 × 103 J (3) 2.26 × 103 J (4) 5.65 × 102 J

Q22.A copper wire is wound on a wooden frame, whose shape is that of an equilateral triangle. If the linear dimension of each side of the frame is increased by a factor of 3, keeping the number of turns of the coil per unit length of the frame the same, then the self inductance of the coil: (1) decreases by a factor of 9 (2) increases by a factor of 27 (3) increases by a factor of 3 (4) decreases by a factor of 9√3

Q22.At some location the horizontal component of earth's magnetic field is 18 × 10−6 T. At this location, magnetic needle of length 0.12 m and pole strength 1.8 Am is suspended from its mid-point using a thread, it makes 45° angles with horizontal in equilibrium. To keep this needle horizontal, the vertical force that should be applied at one of its ends is: (1) 1.8 × 10−5 N (2) 3.6 × 10−5 N (3) 6. 5 × 10−5 N (4) 1.3 × 10−5 N

Q22.The mean intensity of radiation on the surface of the Sun is about 108W/m2. The rms value of the corresponding magnetic field is closest to: (1) 1T (2) 10−2T (3) 102T (4) 10−4T

Q22.An electromagnetic wave of intensity 50Wm−2 enters in a medium of refractive index 'n' without any loss. The ratio of the magnitudes of electric fields, and the ratio of the magnitudes of magnetic fields of the wave before and after entering into the medium are respectively, given by : (1) ( √n1 , √n1 ) (2) (√n, √n) (3) (√n, √n1 ) (4) ( √n1 , √n)

Q23.If the magnetic field of a plane electromagnetic wave is given by (The speed of light = 3 × 108 m/s) B = 100 × 10−6 sin[2π × 2 × 1015(t −xc )] then the maximum electric field associated with it is: (1) 3 × 104 N C−1 (2) 4 × 104 N C−1 (3) 4.5 × 104 N C−1 (4) 6 × 104 N C−1