Practice Questions

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.The correct relation between the degrees of freedom f and the ratio of specific heat γ is: (1) f = γ−12 (2) f = γ+12 (3) f = γ+12 (4) f = γ+11

Q12.A parallel-plate capacitor with plate area A has separation d between the plates. Two dielectric slabs of dielectric constant K1 and K2 of same area A2 and thickness d2 are inserted in the space between the plates. The capacitance of the capacitor will be given by : 2( K1+K2) (1) ε0 + + d K1+K2 K1 A ( 12 K1 K2 ) (2) ε0dA ( 21 K2 ) K1 (3) ε0 + K1+K2 + d 2( K1+K2) K2 ) A ( 12 K1 K2 ) (4) ε0dA ( 21

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.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.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.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 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.A coil having N turns is wound tightly in the form of a spiral with inner and outer radii a and b respectively. Find the magnetic field at centre, when a current I passes through coil : (1) μ0I 8 [ a+ba−b ] (2) 4(a−b)μ0I [ a1 −1b ] (3) μ0I 8 ( a+ba−b ) (4) 2(μ0INb−a) loge( ab )

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.The relative permittivity of distilled water is 81. The velocity of light in it will be: (Given μr = 1) (1) 4. 33 × 107 m s−1 (2) 2. 33 × 107 m s−1 (3) 3. 33 × 107 m s−1 (4) 5. 33 × 107 m s−1

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.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.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.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.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.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.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.Match List I with List II. List I List II (a) Rectifier (i) Used either for stepping up or stepping down the A.C. voltage (b)Stabilizer (ii) Used to convert A.C. voltage into D.C. voltage (c) Transformer(iii)Used to remove any ripple in the rectified output voltage Used for constant output voltage even when the input voltage (d)Filter (iv) or load current change Choose the correct answer from the options given below: (1) (a) −(ii), (b) −(iv), (c) −(i), (d) −(iii) (2) (a) −(ii), (b) −(i), (c) −(iv), (d) −(iii) (3) (a) −(ii), (b) −(i), (c) −(iii), (d) −(iv) (4) (a) −(iii), (b) −(iv), (c) −(i), (d) −(ii)

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.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.For full scale deflection of total 50 divisions, 50 mV voltage is required in galvanometer. The resistance of galvanometer if its current sensitivity is 2 div / mA will be: (1) 1 Ω (2) 2 Ω (3) 5 Ω (4) 4 Ω

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.A simple pendulum of mass ' m ', length ' l ' and charge ′+q′ suspended in the electric field produced by two conducting parallel plates as shown. The value of deflection of pendulum in equilibrium position will be JEE Main 2021 (27 Jul Shift 2) JEE Main Previous Year Paper × × (C1+C2)(d−t) (C1+C2)(d−t) C1( V2−V1) ] (2) tan−1[ mgq C2( V2−V1) ] (1) tan−1[ mgq × × (C1+C2)(d−t) (C1+C2)(d−t) C2( V1+V2) ] (4) tan−1[ mgq C1( V1+V2) ] (3) tan−1[ mgq

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