Practice Questions

Q13. BX and BY are the magnetic field at the centre of two coils of two coils X and Y respectively, each carrying equal current. If coil X has 200 turns and 20 cm radius and coil Y has 400 turns and 20 cm radius, the ratio of BX and BY is JEE Main 2022 (26 Jul Shift 1) JEE Main Previous Year Paper (1) 1 : 1 (2) 1 : 2 (3) 2 : 1 (4) 4 : 1

Q13.If a charge q is placed at the centre of a closed hemispherical non-conducting surface, the total flux passing through the flat surface would be JEE Main 2022 (27 Jun Shift 2) JEE Main Previous Year Paper (1) q (2) q ε0 2ε0 (3) q (4) q 4ε0 2πε0

Q13.If the charge on a capacitor is increased by 2C , the energy stored in it increases by 44%. The original charge on the capacitor is (in C ) (1) 10 (2) 20 (3) 30 (4) 40

Q14.The vertical component of the earth's magnetic field is 6 × 10-5 T at any place where the angle of dip is 37°. 3 The earth's resultant magnetic field at that place will be (Given tan37° = 4) (1) 8 × 10-5 T (2) 6 × 10-5 T (3) 5 × 10-4 T (4) 1 × 10-4 T

Q14.A coil of inductance 1 H and resistance 100 Ω is connected to a battery of 6 V . Determine approximately : (a) The time elapsed before the current acquires half of its steady-state value (b) The energy stored in the magnetic field associated with the coil at an instant 15 ms after the circuit is switched on. (Given ln 2 = 0. 693, e −32 = 0. 25) (1) t = 10 ms; U = 2 mJ (2) t = 10 ms; U = 1 mJ (3) t = 7 ms; U = 1 mJ (4) t = 7 ms; U = 2 mJ

Q14.The susceptibility of a paramagnetic material is 99. The permeability of the material in Wb /A −m, is [Permeability of free space μ0 = 4π × 10−7 Wb /A −m] (1) 4π × 10−5 (2) 4π × 10−6 (3) 4π × 10−7 (4) 4π × 10−4

Q14.The electromagnetic waves travel in a medium at a speed of 2 . 0 × 108 m s-1. The relative permeability of the medium is 1 . 0. The relative permittivity of the medium will be (1) 2 . 25 (2) 4 . 25 (3) 6 . 25 (4) 8 . 25

Q14.Three identical charged balls each of charge 2C are suspended from a common point P by silk threads of 2 m each (as shown in figure). They form an equilateral triangle of side 1 m . The ratio of net force on a charged ball to the force between any two charged balls will be (1) √3 : 1 (2) √3 : 2 (3) 1 : 1 (4) 1 : 4

Q14.A direct current of 4 A and an alternating current of peak value 4 A flow through resistance of 3 Ω and 2 Ω respectively. The ratio of heat produced in the two resistances in same interval of time will be : (1) 3 : 2 (2) 3 : 1 (3) 3 : 4 (4) 4 : 3

Q14.A coil is placed in a time varying magnetic field. If the number of turns in the coil were to be halved and the radius of wire doubled, the electrical power dissipated due to the current induced in the coil would be (Assume the coil to be short circuited.) (1) Doubled (2) The same (3) Quadrupled (4) Halved

Q14.The combination of two identical cells, whether connected in series or parallel combination provides the same current through an external resistance of 2 Ω. The value of internal resistance of each cell is (1) 2 Ω (2) 4 Ω (3) 6 Ω (4) 8 Ω

Q14.The aperture of the objective is 24. 4 cm. The resolving power of this telescope, if a light of wavelength ∘ 2440 A is used to see the object will be (1) 8. 1 × 106 (2) 10. 0 × 107 (3) 8. 2 × 105 (4) 1. 0 × 10−8

Q14.At a certain place the angle of dip is 30° and the horizontal component of earth's magnetic field is 0. 5 G . The earth's total magnetic field (in G), at that certain place, is JEE Main 2022 (29 Jun Shift 1) JEE Main Previous Year Paper (1) 1 (2) 1 √3 2 (3) √3 (4) 1

Q14.A series LCR circuit has L = 0. 01 H, R = 10 Ω and C = 1 μF and it is connected to ac voltage of amplitude (Vm) 50 V . At frequency 60% lower than resonant frequency, the amplitude of current will be approximately (1) 466 mA (2) 312 mA (3) 238 mA (4) 196 mA

Q14.What will be the most suitable combination of three resistors A = 2 Ω, B = 4 Ω, C = 6 Ω so that ( 223 )Ω is equivalent resistance of combination? (1) Parallel combination of A and C connected in series with B (2) Parallel combination of A and B connected in series with C (3) Series combination of A and C connected in parallel with B. (4) Series combination of B and C connected in parallel with A.

Q14.The electric current in a circular coil of 2 turns produces a magnetic induction B1 at its centre. The coil is unwound and is rewound into a circular coil of 5 turns and the same current produces a magnetic induction B2 JEE Main 2022 (25 Jul Shift 2) JEE Main Previous Year Paper at its centre. The ratio of B2 is: B1 (1) 5 (2) 25 2 4 (3) 5 (4) 25 4 2

Q14.A light wave travelling linearly in a medium of dielectric constant 4, incidents on the horizontal interface separating medium with air. The angle of incidence for which the total intensity of incident wave will be reflected back into the same medium will be : (Given : relative permeability of medium 𝜇r = 1) (1) 10° (2) 20° (3) 30° (4) 60° JEE Main 2022 (25 Jun Shift 1) JEE Main Previous Year Paper

Q14.Given below are two statements : One is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A) : In an uniform magnetic field, speed and energy remains the same for a moving charged particle. Reason (R): Moving charged particle experiences magnetic force perpendicular to its direction of motion. JEE Main 2022 (24 Jun Shift 1) JEE Main Previous Year Paper (1) Both Assertion and Reason are true and Reason is (2) Both Assertion and Reason are true but Reason is the correct explanation of Assertion. NOT the correct explanation of Assertion. (3) Assertion is true but Reason is false. (4) Assertion is false but Reason is true.

Q14.A metal surface is illuminated by a radiation of wavelength 4500 A . The ejected photo-electron enters a constant magnetic field of 2 mT making an angle of 90° with the magnetic field. If it starts revolving in a circular path of radius 2 mm, the work function of the metal is approximately (1) 1. 36 eV (2) 1. 69 eV (3) 2. 78 eV (4) 2. 23 eV

Q14.A velocity selector consists of electric field 𝐸= 𝐸 ^k and magnetic field 𝐵= 𝐵 ^j with 𝐵= 12 mT. The value 𝐸 required for an electron of energy 728eV moving along the positive x-axis to pass undeflected is (Given, mass of electron = 9 . 1 × 10-31 kg) (1) 192 kV m-1 (2) 192 mV m-1 (3) 9600 kV m-1 (4) 16 kV m-1

Q14.The equation of current in a purely inductive circuit is 5sin49𝜋𝑡- 30°. If the inductance is 30mH then the equation for the voltage across the inductor, will be (1) 1 . 47sin49𝜋𝑡- 30° (2) 1 . 47sin49𝜋𝑡+ 60° (3) 23 . 1sin49𝜋𝑡- 30° (4) 23 . 1sin49𝜋𝑡+ 60°

Q14.A transformer operating at primary voltage 8 kV and secondary voltage 160 V serves a load of 80 kW. Assuming the transformer to be ideal with purely resistive load and working on unity power factor, the loads in the primary and secondary circuit would be (1) 800 Ω and 1. 06 Ω (2) 10 Ω and 500 Ω (3) 800 Ω and 0. 32 Ω (4) 1. 06 Ω and 500 Ω

Q14.In a series LR circuit XL = R and power factor of the circuit is P1 . When capacitor with capacitance C such that XL = XC is put in series, the power factor becomes P2 . The ratio P1 is P2 (1) 1 (2) 1 2 √2 (3) √3 (4) 2 : 1 √2

Q14.The magnetic flux through a coil perpendicular to its plane is varying according to the relation ϕ = (5t3 + 4t2 + 2t −5) Weber. If the resistance of the coil is 5 ohm , then the induced current through the coil at t = 2 s will be, (1) 15. 6 A (2) 16. 6 A (3) 17. 6 A (4) 18. 6 A

Q14.To increase the resonant frequency in series LCR circuit, (1) Source frequency should be increased (2) Another resistance should be added in series with the first resistance. (3) Another capacitor should be added in series with (4) The source frequency should be decreased the first capacitor