Practice Questions

Q11.A cube is placed inside an electric field, →𝐸= 150𝑦2^j The side of the cube is 0 . 5 m and is placed in the field as shown in the given figure. The charge inside the cube is: (1) 8 . 3 × 10-11C (2) 3 . 8 × 10-11C (3) 3 . 8 × 10-12C (4) 8 . 3 × 10-12C

Q11.Consider a galvanometer shunted with 5 Ω resistance and 2% of current passes through it. What is the resistance of the given galvanometer? (1) 245 Ω (2) 344 Ω (3) 300 Ω (4) 226 Ω

Q11. Calculate the amount of charge on capacitor of 4 μF. The internal resistance of battery is 1Ω : (1) 4 μC (2) 8 μC (3) 16 μC (4) zero

Q11.In the given figure, there is a circuit of potentiometer of length 𝐴𝐵= 10 m. The resistance per unit length is 0 . 1 Ω per cm. Across 𝐴𝐵, a battery of emf 𝐸 and internal resistance 𝑟 is connected. The maximum value of emf measured by this potentiometer is: JEE Main 2021 (25 Jul Shift 1) JEE Main Previous Year Paper (1) 5 V (2) 2 . 25 V (3) 6 V (4) 2 . 75 V

Q11.An electron with kinetic energy K1 enters between parallel plates of a capacitor at an angle α with the plates. It leaves the plates at angle β with kinetic energy K2. Then the ratio of kinetic energies K1 : K2 will be : (1) sin2 β (2) cos β cos2 α sin α (3) cos β (4) cos2 β cos α cos2 α

Q11.Three capacitors C1 = 2 μF, C2 = 6 μF and C3 = 12 μF are connected as shown in the figure. Find the ratio of the charges on capacitors C1, C2 and C3 respectively. JEE Main 2021 (27 Aug Shift 2) JEE Main Previous Year Paper (1) 3 : 4 : 4 (2) 2 : 3 : 3 (3) 2 : 1 : 1 (4) 1 : 2 : 2

Q12.Find the electric field at point P (as shown in figure) on the perpendicular bisector of a uniformly charged thin wire of length L carrying a charge Q. The distance of the point P from the centre of the rod is a = √32 L (1) Q (2) Q 3πε0L2 2√3πε0L2 (3) √3Q (4) Q 4πε0L2 4πε0L2

Q12.If qf is the free charge on the capacitor plates and qb is the bound charge on the dielectric slab of dielectric constant k placed between the capacitor plates, then bound charge qb can be expressed as : − k ) (1) qb = qf(1 1 ) (2) qb = qi(1 −1 √k 1 ) + k (3) qb = qf(1 1 ) (4) qb = qf(1 + √k

Q12.Two cells of emf 2E and E with internal resistance r1 and r2 respectively are connected in series to an external resistor R (see figure). The value of R, at which the potential difference across the terminals of the first cell becomes zero is (1) r1 + r2 (2) r12 −r2 (3) r1 2 + r2 (4) r1 −r2

Q12.A tuning fork A of unknown frequency produces 5 beats s−1 with a fork of known frequency 340 Hz. When fork A is filed, the beat frequency decreases to 2 beats s−1 . What is the frequency of fork A ? (1) 335 Hz (2) 338 Hz (3) 345 Hz (4) 342 Hz

Q12.Choose the correct option. (1) True dip is not mathematically related to apparent (2) True dip is less than apparent dip. dip. (3) True dip is always greater than the apparent dip. (4) True dip is always equal to apparent dip.

Q12.A conducting wire of length l, area of crosssection A and electric resistivity ρ is connected between the terminals of a battery. A potential difference V is developed between its ends, causing an electric current. If the JEE Main 2021 (16 Mar Shift 1) JEE Main Previous Year Paper length of the wire of the same material is doubled and the area of cross-section is halved, the resultant current would be___ (1) 1 V A (2) 3 V A 4 ρl 4 ρl ρl 1 (3) V A (4) 4 VρlA 4

Q12.Which of the following statements are correct? (A) Electric monopoles do not exist whereas magnetic monopoles exist. (B) Magnetic field lines due to a solenoid at its ends and outside cannot be completely straight and confined. (C) Magnetic field lines are completely confined within a toroid. (D) Magnetic field lines inside a bar magnet are not parallel. (E) χ = −1 is the condition for a perfect diamagnetic material, where χ is its magnetic susceptibility. Choose the correct answer from the options given below : (1) (C) and (E) only (2) (B) and (D) only (3) (A) and (B) only (4) (B) and (C) only

Q12.A linearly polarised electromagnetic wave in vacuum is 𝐸= 3 . 1cos1 . 8𝑧- 5 . 4 × 106𝑡 ^i N C-1 is incident normally on a perfectly reflecting wall at 𝑧= 𝑎. Choose the correct option. (1) The wavelength is 5 . 4 m. (2) The frequency of electromagnetic wave is 54 × 104 Hz. (3) The transmitted wave will be (4) The reflected wave will be 3 . 1cos1 . 8𝑧- 5 . 4 × 106𝑡 ^i N / C. 3 . 1cos1 . 8z + 5 . 4 × 106𝑡 ^i N C-1.

Q12.A cube of side 𝑎 has point charges +Q located at each of its vertices except at the origin where the charge is -Q . The electric field at the centre of cube is: JEE Main 2021 (24 Feb Shift 1) JEE Main Previous Year Paper -𝑄 𝑄 (1) ^𝑥+ ^𝑦+ ^𝑧 (2) ^𝑥+ ^𝑦+ ^𝑧 3√3𝜋𝜀0𝑎2 3√3𝜋𝜀0𝑎2 (3) -2𝑄 ^𝑥+ ^𝑦+ ^𝑧 (4) 2𝑄 ^𝑥+ ^𝑦+ ^𝑧 3√3𝜋𝜀0𝑎2 3√3𝜋𝜀0𝑎2

Q12.Choose the incorrect statement: (a) The electric lines of force entering into a Gaussian surface provide negative flux. (b) A charge 𝑞 is placed at the centre of a cube. The flux through all the faces will be the same. (c) In a uniform electric field net flux through a closed Gaussian surface containing no net charge, is zero. (d) When an electric field is parallel to a Gaussian surface, it provides a finite non-zero flux. Choose the most appropriate answer from the options given below: (1) (b) and (d) Only (2) (c) and (d) Only (3) (a) and (c) Only (4) (d) Only JEE Main 2021 (31 Aug Shift 2) JEE Main Previous Year Paper

Q12.A capacitor is connected to a 20 V battery through a resistance of 10Ω . It is found that the potential difference across the capacitor rises to 2 V in 1 μs . The capacitance of the capacitor is ________μF . Given In 10 = 0 . 105 9 (1) 0 . 95 (2) 9 . 52 (3) 1 . 85 (4) 0 . 105 JEE Main 2021 (01 Sep Shift 2) JEE Main Previous Year Paper

Q12.The fractional change in the magnetic field intensity at a distance r from centre on the axis of current carrying coil of radius a to the magnetic field intensity at the centre of the same coil is: (Take r < a) (1) 2 a2 (2) 3 a2 3 r2 2 r2 (3) 3 r2 (4) 2 r2 2 a2 3 a2

Q12.Five identical cells each of internal resistance 1 Ω and emf 5 V are connected in series and in parallel with an external resistance R. For what value of R, current in series and parallel combination will remain the same? (1) 1 Ω (2) 5 Ω (3) 25 Ω (4) 10 Ω JEE Main 2021 (27 Aug Shift 1) JEE Main Previous Year Paper

Q12.A current of 5 A is passing through a non-linear magnesium wire of cross-section 0. 04 m2 . At every point the direction of current density is at an angle of 60° with the unit vector of area of cross-section. The magnitude of electric field at every point of the conductor is: (resistivity of magnesium ρ = 44 × 10−8 Ωm) (1) 11 × 10−2 V m−1 (2) 11 × 10−7 V m−1 (3) 11 × 10−5 V m−1 (4) 11 × 10−3 V m−1

Q12.Magnetic fields at two points on the axis of a circular coil at a distance of 0. 05 m and 0. 2 m from the centre are in the ratio 8 : 1 . The radius of coil is _______ . (1) 0. 15 m (2) 0. 2 m (3) 0. 1 m (4) 1. 0 m

Q12.An AC source rated 220 V, 50 Hz is connected to a resistor. The time taken by the current to change from its maximum to the rms value is : (1) 2. 5 ms (2) 25 ms (3) 2. 5 s (4) 0. 25 ms

Q12.The figure shows a circuit that contains four identical resistors with resistance R = 2. 0 Ω, two identical inductors with inductance L = 2. 0 mH and an ideal battery with E.M.F. E = 9 V. The current i just after the switch S is closed will be: JEE Main 2021 (24 Feb Shift 2) JEE Main Previous Year Paper (1) 9 A (2) 3. 37 A (3) 2. 25 A (4) 3. 0 A

Q12.A current of 10 A exists in a wire of cross-sectional area of 5 mm2 with a drift velocity of 2 × 10−3 m s−1. The number of free electrons in each cubic meter of the wire is (1) 2 × 106 (2) 625 × 1025 (3) 2 × 1025 (4) 1 × 1023

Q12.The magnetic field in a region is given by B = B0( a )ˆk the x and y axes. The loop is moved with a constant velocity →v= v0ˆi. The emf induced in the loop is : JEE Main 2021 (16 Mar Shift 2) JEE Main Previous Year Paper (1) B0v20 d (2) B0v0d 2a 2a (3) B0v0d2 (4) B0v0d2 a 2a