Practice Questions

Q14.A current of 1 . 5 A is flowing through a triangle, of side 9 cm each. The magnetic field at the centroid of the triangle is : (Assume that the current is flowing in the clockwise direction.) (1) 2√3 × 10-5 T, inside the plane of triangle (2) 2√3 × 10-7 T, outside the plane of triangle (3) 3 × 10-7 T, outside the plane of triangle (4) 3 × 10-5 T, inside the plane of triangle

Q14.An AC current is given by I = I1sinωt + I2cosωt. A hot wire ammeter will give a reading: 2 2 −I 2 +I 1 1 2 2 (1) √I 2 (2) √I 2 2 (3) I1+I2 (4) I1+I2 √2 2√2

Q14.In the reported figure, a capacitor is formed by placing a compound dielectric between the plates of parallel plate capacitor. The expression for the capacity of the said capacitor will be: (Given the area of the plate = A ) (1) 15 Kε0 A (2) 15 Kε0 A 34 d 6 d (3) 25 Kε0 A (4) 9 Kε0 A 6 d 6 d

Q14.Five equal resistances are connected in a network as shown in figure. The net resistance between the points A and B is : JEE Main 2021 (26 Feb Shift 1) JEE Main Previous Year Paper (1) R (2) R2 (3) 3R2 (4) 2R

Q14.A hairpin like shape as shown in figure is made by bending a long current carrying wire. What is the magnitude of a magnetic field at point P which lies on the centre of the semicircle ? (1) μ0I + 4πr (2 −π) (2) μ0I4πr (2 π) (3) μ0I + 2πr (2 π) (4) μ0I2πr (2 −π)

Q14.An inductor coil stores 64 J of magnetic field energy and dissipates energy at the rate of 640 W when a current of 8 A is passed through it. If this coil is joined across an ideal battery, find the time constant of the circuit (in s). (1) 0. 4 (2) 0. 2 (3) 0. 125 (4) 0. 8

Q14.If you are provided a set of resistances, 2 Ω, 4 Ω, 6 Ω and 8 Ω. Connect these resistances to obtain an equivalent resistance of 46 3 Ω. (1) 2 Ω and 6 Ω are in parallel with 4 Ω and 8 Ω in series (2) 4 Ω and 6 Ω are in parallel with 2 Ω and 8 Ω in series (3) 2 Ω and 4 Ω are in parallel with 6 Ω and 8 Ω in series (4) 6 Ω and 8 Ω are in parallel with 2 Ω and 4 Ω in series

Q14.Consider the diffraction pattern obtained from the sunlight incident on a pinhole of diameter 0. 1 μm. If the diameter of the pinhole is slightly increased, it will affect the diffraction pattern such that (1) its size increases, and intensity increases (2) its size decreases, and intensity decreases (3) its size decreases, but intensity increases (4) its size increases, but intensity decreases

Q14.In the Young's double slit experiment, the distance between the slits varies in time as 𝑑𝑡= 𝑑0 + 𝑎0 sin𝜔𝑡; where 𝑑0, 𝜔 and 𝑎0 are constants. The difference between the largest fringe width and the smallest fringe width obtained over time is given as: (1) 2𝜆𝐷𝑑02 2 (2) 2𝜆𝐷𝑎02 2 𝑑0 - 𝑎0 𝑑0 - 𝑎0 𝜆𝐷 (3) 𝜆𝐷 2𝑎0 (4) 𝑑0 + 𝑎0 𝑑0

Q15.An alternating current is given by the equation i = i1 sin ωt + i2 cos ωt. The rms current will be: (1) 1 (i1 + i2)2 (2) 1 (i1 + i2) √2 √2 2 (3) 1 1 1 2 (i21 + i22) 2 (4) √21 (i21 + i22)

Q15. AC voltage V (t) = 20 sin ωt of frequency 50 Hz is applied to a parallel plate capacitor. The separation between the plates is 2 mm and the area is 1 m2 . The amplitude of the oscillating displacement current for the applied AC voltage is [Take ε0 = 8. 85 × 10−12 F m−1] JEE Main 2021 (20 Jul Shift 1) JEE Main Previous Year Paper (1) 21. 14 μA (2) 83. 37 μA (3) 27. 79 μA (4) 55. 58 μA

Q15.Two ions having same mass have charges in the ratio 1 : 2 . They are projected normally in a uniform magnetic field with their speeds in the ratio 2 : 3 . The ratio of the radii of their circular trajectories is, (1) 1 : 4 (2) 4 : 3 (3) 3 : 1 (4) 2 : 3

Q15.Intensity of sunlight is observed as 0. 092 Wm−2 at a point in free space. What will be the peak value of magnetic field at that point ? (ε0 = 8. 85 × 10−12 C2 N−1 m−2) (1) 2. 77 × 10−8 T (2) 1. 96 × 10−8 T (3) 8. 31 T (4) 5. 88 T

Q15.The time taken for the magnetic energy to reach 25% of its maximum value, when a solenoid of resistance R, inductance L is connected to a battery, is : (1) L ln5 (2) infinite R (3) R L ln2 (4) RL ln10

Q15.At an angle of 30° to the magnetic meridian, the apparent dip is 45°. Find the true dip: (1) tan−1 √3 (2) tan−1 1 √3 (3) tan−1 2 (4) tan−1 √32 √3

Q15.A constant magnetic field of 1 T is applied in the x > 0 region. A metallic circular ring of radius 1 m is moving with a constant velocity of 1 m s−1 along the x-axis. At t = 0 s, the centre O of the ring is at x = −1 m. What will be the value of the induced emf in the ring at t = 1 s ? (Assume the velocity of the ring does not change.) JEE Main 2021 (27 Aug Shift 2) JEE Main Previous Year Paper (1) 0 V (2) 2 V (3) 2π V (4) 1 V

Q15.Two coherent light sources having intensity in the ratio 2x produce an interference pattern. The ratio Imax−Imin Imax+Imin will be (1) 2√2x (2) √2x x+1 2x+1 (3) 2√2x (4) √2x 2x+1 x+1 JEE Main 2021 (25 Feb Shift 1) JEE Main Previous Year Paper

Q15.Figure A and B shown two long straight wires of circular cross-section ( a and b with a < b ), carrying current I which is uniformly distributed across the cross-section. The magnitude of magnetic field B varies with radius r and can be represented as: JEE Main 2021 (27 Jul Shift 2) JEE Main Previous Year Paper (1) (2) (3) (4)

Q15.Find the peak current and resonant frequency of the following circuit (as shown in figure). (1) 2 A and 50 Hz (2) 0. 2 A and 100 Hz (3) 2 A and 100 Hz (4) 0. 2 A and 50 Hz

Q15.In Young's double slit arrangement, slits are separated by a gap of 0. 5 mm , and the screen is placed at a distance of 0. 5 m from them. The distance between the first and the third bright fringe formed when the slits o are illuminated by a monochromatic light of 5890 A is :- (1) 1178 × 10–9 m (2) 1178 × 10–6 m (3) 1178 × 10–12 m (4) 5890 × 10–7 m

Q15.An object is placed at the focus of concave lens having focal length f. What is the magnification and distance of the image from the optical centre of the lens? (1) 4 1 , f4 (2) 12 , f2 (3) Very high, ∞ (4) 1, ∞

Q15.In the given circuit the AC source has ω = 100 rad s−1 . Considering the inductor and capacitor to be ideal, what will be the current I flowing through the circuit? (1) 5. 9 A (2) 6 A (3) 0. 94 A (4) 3. 16 A

Q15.Two capacitors of capacities 2C and C are joined in parallel and charged up to potential V . The battery is removed and the capacitor of capacity C is filled completely with a medium of dielectric constant K. The potential difference across the capacitors will now be: (1) V (2) V K+2 K (3) 3V (4) 3V K+2 K

Q15.For the given circuit the current 𝑖 through the battery when the key in closed and the steady state has been reached is (1) 10 A (2) 6 A (3) 25 A (4) 0 A

Q16.The stopping potential for electrons emitted from a photosensitive surface illuminated by light of wavelength 491 nm is 0. 710 V. When the incident wavelength is changed to a new value, the stopping potential is 1. 43 V. The new wavelength is : (1) 382 nm (2) 309 nm (3) 329 nm (4) 400 nm