Practice Questions

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.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.An electron of mass me and a proton of mass mp = 1836 me are moving with the same speed. The ratio of their de Broglie wavelength λelectron will be : λproton (1) 1836 (2) 18361 (3) 918 (4) 1

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.Match List-I with List-II List-i List-II π 2 ; current Phase difference between current and voltage in a purely a i leads resistive AC circuit voltage bPhase difference between current and ii zero voltage in a pure inductive AC circuit Phase difference between current and π 2 ; current lags c iii voltage in a pure capacitive AC circuit voltage dPhase difference between current and iv tan−1( XC−XLR ) voltage in an LCR series circuit Choose the most appropriate answer from the options given below : (1) (a) −(i), (b) −(iii), (c) −(iv), (d) −(ii) (2) (a) −(ii), (b) −(iv), (c) −(iii), (d) −(i) (3) (a) −(ii), (b) −(iii), (c) −(iv), (d) −(i) (4) (a )-( ii ) , (b) −(iii), (c) −(i), (d) −(iv)

Q15.The electric field in a plane electromagnetic wave is given by, E = 50 sin(500x −10 × 1010t) V m−1 . The velocity of an electromagnetic wave in this medium is: (Given c = the speed of light in vacuum). (1) 23 c (2) c (3) 2c (4) 23 c

Q15.The refractive index of a converging lens is 1. 4. What will be the focal length of this lens if it is placed in a medium of same refractive index ? (Assume the radii of curvature of the faces of lens are R1 and R2 respectively) (1) 1 (2) Infinite (3) R1R2 (4) Zero R1−R2

Q16.In the given figure, a battery of emf E is connected across a conductor PQ of length l and different area of cross-sections having radii r1 and r2(r2 < r1). Choose the correct option as one moves from P to Q. (1) Drift velocity of electron increases. (2) Electric field decreases. (3) Electron current decreases. (4) All of these

Q16.An object is placed beyond the centre of curvature C of the given concave mirror. If the distance of the object is d1 from C and the distance of the image formed is d2 from C, the radius of curvature of this mirror is: (1) 2 d1 d2 (2) 2 d1 d2 d1+d2 d1−d2 (3) d1 d2 (4) d1 d2 d1+d2 d1−d2

Q16.A 10 Ω resistance is connected across 220 V −50 Hz AC supply. The time taken by the current to change from its maximum value to the rms value is: (1) 2. 5 ms (2) 1. 5 ms (3) 3. 0 ms (4) 4. 5 ms

Q16.A ray of light passes from a denser medium to a rarer medium at an angle of incidence i. The reflected and refracted rays make an angle of 90° with each other. The angle of reflection and refraction are respectively r and r′. The critical angle is given by, JEE Main 2021 (22 Jul Shift 1) JEE Main Previous Year Paper (1) sin−1(cot r) (2) tan−1(sin i) (3) sin−1(tanr′) (4) sin−1(tan r)

Q16.Curved surfaces of a plano-convex lens of refractive index μ1 and a plano-concave lens of refractive index μ2 have equal radius of curvature as shown in figure. Find the ratio of radius of curvature to the focal length of the combined lenses (1) 1 (2) 1 μ2−μ1 μ1−μ2 (3) μ2 −μ1 (4) μ1 −μ2

Q16.In a photoelectric experiment, ultraviolet light of wavelength 280 nm is used with lithium cathode having work function ϕ = 2. 5 eV. If the wavelength of incident light is switched to 400 nm, find out the change in the stopping potential. (h = 6. 63 × 10−34 J s, c = 3 × 108 m s−1) JEE Main 2021 (26 Aug Shift 1) JEE Main Previous Year Paper (1) 1. 1 V (2) 0. 6 V (3) 1. 3 V (4) 1. 9 V

Q16.A plane electromagnetic wave propagating along y-direction can have the following pair of electric field (→E) and magnetic field components. (→B) (1) Ey, By or Ez, Bz (2) Ey, Bx or Ex, By (3) Ex, Bz or Ez, Bx (4) Ex, By or Ey, Bx

Q16.What happens to the inductive reactance and the current in a purely inductive circuit if the frequency is halved ? (1) Both, inductive reactance and current will (2) Inductive reactance will be halved and be halved. current will be doubled.. (3) Inductive reactance will be doubled and (4) Both, inducting reactance and current will be current will be halved. doubled JEE Main 2021 (17 Mar Shift 2) JEE Main Previous Year Paper

Q16.An electron of mass m and a photon have same energy E. The ratio of wavelength of electron to that of photon is : ( c being the velocity of light) (1) 1 2m 21 (2) 1 E 12 c ( E ) c ( 2m ) (3) E 21 (4) c(2mE) 12 ( 2 m )

Q16.A light beam is described by E = 800 sin ω(t −xc ). An electron is allowed to move normal to the propagation of light beam with a speed of 3 × 107 m s−1 . What is the maximum magnetic force exerted on the electron? (1) 1. 28 × 10−21 N (2) 12. 8 × 10−18 N (3) 1. 28 × 10−18 N (4) 12. 8 × 10−17 N JEE Main 2021 (26 Aug Shift 2) JEE Main Previous Year Paper

Q16.Two plane mirrors M1 and M2 are at right angle to each other shown. A point source P is placed at a and 2a meter away from M1 and M2 respectively. The shortest distance between the images thus formed is : (Take √5 = 2. 3) (1) 2. 3 a (2) 2√10a (3) 4. 6a (4) 3a

Q16.A plane electromagnetic wave of frequency 500 MHz is traveling in a vacuum along the y−direction. At a → particular point in space and time, B = 8. 0 × 10−8ˆz T. The value of the electric field at this point is:(speed of light = 3 × 108 ms−1 ) ˆx, ˆy,ˆz are unit vectors along x, y and z direction. (1) −24ˆx V m−1 (2) 2. 6ˆx V m−1 (3) 24ˆx V m−1 (4) −2. 6ˆx V m−1 JEE Main 2021 (16 Mar Shift 1) JEE Main Previous Year Paper

Q16.The magnetic field vector of an electromagnetic wave is given by 𝐵= 𝐵0 ^i √2 represents unit vector along 𝑥 and 𝑦-axis respectively. At 𝑡= 0 s, two electric charges 𝑞1 of 4𝜋 coulomb and 𝜋 3𝜋 of 2𝜋 coulomb located at 0, 0, and 0, 0, respectively, have the same velocity of 0 . 5c ^i, (where 𝑞2 𝑘 𝑘, 𝑐 is the velocity of light ). The ratio of the force acting on charge 𝑞1 to 𝑞2 is : (1) 1 : √2 (2) 2√2 : 1 (3) √2 : 1 (4) 2 : 1

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

Q16.A square loop of side 20 cm and resistance 1 Ω is moved towards right with a constant speed 𝑣0 . The right arm of the loop is in a uniform magnetic field of 5 T . The field is perpendicular to the plane of the loop and is going into it. The loop is connected to a network of resistors each of value 4Ω . What should be the value of 𝑣0 so that a steady current of 2 mA flows in the loop ? JEE Main 2021 (01 Sep Shift 2) JEE Main Previous Year Paper (1) 10-2 cm s-1 (2) 1 m s-1 (3) 1 cm s-1 (4) 102 m s-1

Q16.A 100Ω resistance, a 0. 1μF capacitor and an inductor are connected in series across a 250 V supply at variable frequency. Calculate the value of inductance of inductor at which resonance will occur. Given that the resonant frequency is 60 Hz. (1) 0. 70H (2) 70. 3 mH (3) 7. 03 × 10−5H (4) 70. 3 H

Q16.An oil drop of the radius 2 mm with a density 3 g cm−3 is held stationary under a constant electric field 3. 55 × 105 V m−1 in the Millikan's oil drop experiment. What is the number of excess electrons that the oil drop will possess? (consider g = 9. 81 m s−2). (1) 48. 8 × 1011 (2) 1. 73 × 1010 (3) 17. 3 × 1010 (4) 1. 73 × 1012