Practice Questions

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 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 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 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.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 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.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.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.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

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 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.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.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.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 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.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

Q13.An electric bulb of 500 W at 100 V is used in a circuit having a 200 V supply. Calculate the resistance R to be connected in series with the bulb so that the power delivered by the bulb is 500 W. (1) 30 Ω (2) 5 Ω (3) 20 Ω (4) 10 Ω

Q13.The equivalent resistance of the given circuit between the terminals 𝐴 and 𝐵 is : 9 (1) 0 Ω (2) Ω 2 (3) 3 Ω (4) 1 Ω

Q13.A small square loop of side a and one turn is placed inside a larger square loop of side b and one turn (b ≫a). The two loops are coplanar with their centres coinciding. If a current I is passed in the square loop of side b, then the coefficient of mutual inductance between the two loops is : (1) 4π μ0 8√2 a2b (2) 4πμ0 8√2 b2a (3) μ0 8√2 (4) μ0 8√2 4π b 4π a

Q13.What will be the magnitude of the electric field at point O as shown in the figure? Each side of the figure is l and perpendicular to the other? (1) 1 q (2) 1 q 4πε0 l2 4πε0 (2l2) (2√2 −1) (3) q (4) 1 2q 4πε0(2l)2 4πε0 2l2 (√2)

Q13. A capacitor of capacitance C = 1 μF is suddenly connected to a battery of 100 V through a resistance R = 100 Ω. The time taken for the capacitor to be charged to get 50 V is: JEE Main 2021 (27 Jul Shift 1) JEE Main Previous Year Paper (Take ln 2 = 0. 69 ) (1) 1. 44 × 10−4 s (2) 3. 33 × 10−4 s (3) 0. 69 × 10−4 s (4) 0. 30 × 10−4 s

Q13.In the given potentiometer circuit arrangement, the balancing length AC is measured to be 250 cm. When the galvanometer connection is shifted from point (1) to point (2) in the given diagram, the balancing length becomes 400 cm. The ratio of the emf of two cells ε1 is: ε2 (1) 5 (2) 8 3 5 (3) 4 (4) 3 3 2 JEE Main 2021 (25 Jul Shift 2) JEE Main Previous Year Paper