Practice Questions

Q12.Consider the force F on a charge ' q' due to a uniformly charged spherical shell of radius R carrying charge Q distributed uniformly over it. Which one of the following statements is true for F , if ' q' is placed at distance r from the centre of the shell? (1) F = 1 Qq for r < R (2) 1 qQ > F > 0 for r < R 4π∈0 R2 4π∈0 R2 (3) F = 1 Qq for r > R (4) F = 1 Qq for all r 4π∈0 r2 4π∈0 r2 JEE Main 2020 (06 Sep Shift 2) JEE Main Previous Year Paper

Q12.A particle of charge q and mass m is moving with a velocity −vˆi(v ≠0) → Y −Z plane at distance d. If there is magnetic field B = B0ˆk, the minimum value of v for which the particle will not hit the screen is : (1) qdB0 (2) 2qdB0 3m m (3) qdB0 (4) qdB0 m 2m

Q12.In the figure, potential difference between A and B is: (1) 10 V (2) 5 V (3) 15 V (4) 0 V

Q12.A capacitor C is fully charged with voltage V0 . After disconnecting the voltage source, it is connected in parallel with another uncharged capacitor of capacitance C . The energy loss in the process after the charge is 2 distributed between the two capacitors is : (1) 2 1 CV 02 (2) 13 CV 02 (3) 4 1 CV 02 (4) 16 CV 02

Q12.Consider four conducing materials copper, tungsten, mercury and aluminum with resistivity ρC, ρT, ρM and ρA respectively. Then : (1) ρC > ρA > ρT (2) ρM > ρA > ρC (3) ρA > ρT > ρC (4) ρA > ρM > ρC JEE Main 2020 (02 Sep Shift 1) JEE Main Previous Year Paper

Q12.The figure shows a region of length ' 𝓁 ' with a uniform magnetic field of 0. 3 T in it and a proton entering the region with velocity 4 × 105 m s−1 making an angle 60° with the field. If the proton completes 10 revolution by the time it cross the region shown, ' 𝓁 ' is close to (mass of proton = 1. 67 × 10−27 kg, charge of the proton = 1. 6 × 10−19 C) (1) 0. 11 m (2) 0. 88 m (3) 0. 44 m (4) 0. 22 m

Q12.A parallel plate capacitor has plate of length l, width w and separation of plates is d. It is connected to a battery of emf V . A dielectric slab of the same thickness d and of dielectric constant K = 4 is being inserted between the plates of the capacitor. At what length of the slab inside plates, will the energy stored in the capacitor be two times the initial energy stored? (1) 2l (2) l 3 3 (3) l (4) l 4 2

Q12.A capacitor is made of two square plates each of side ‘ a ’ making a very small angle α between them, as shown in figure. The capacitance will be close to: (1) ∈0a2 d (1 −αa2d ) (2) ∈0a2d (1 −αa4d ) (3) ∈0a2 d (1 + αad ) (4) ∈0a2d (1 −3αa2d )

Q12.Effective capacitance of parallel combination of two capacitors C1 and C2 is 10μF. When these capacitors are individually connected to a voltage source of 1V, the energy stored in the capacitor C2 is 4 times that of C1. If these capacitors are connected in series, their effective capacitance will be: (1) 4.2μF (2) 3.2μF (3) 1.6μF (4) 8.4μF

Q12.A long solenoid of radius R carries a time (t) dependent current I(t) = I0t(1 −t) . A ring of radius 2R is placed coaxially near its middle. During the time interval 0 ≤t ≤1, the induced current (IR) and the induced EMF(VR) in the ring change as: (1) Direction of IR remains unchanged and VR is (2) At t = 0.25 direction of IR reverses and VR is maximum at t = 0.5 maximum (3) Direction of IR remains unchanged and VR is (4) At t = 0.5 direction of IR reverses and VR is zero at t = 0.25 zero

Q13.A small bar magnet is placed with its axis at 30o with an external magnetic field of 0. 06 T experiences a torque of 0. 018 Nm. The minimum work required to rotate it from its stable to unstable equilibrium position is: (1) 6. 4 × 10−2 J (2) 9. 2 × 10−3 J (3) 7. 2 × 10−2 J (4) 11. 7 × 10−3 J

Q13. The figure gives experimentally measured B vs. H variation in a ferromagnetic material. The retentivity, coercivity and saturation, respectively, of the material are: JEE Main 2020 (07 Jan Shift 2) JEE Main Previous Year Paper (1) 1.5T, 50A/m and 1.0T (2) 1.5T, 50A/m and 1.0T (3) 150A/m, 1.0T and 1.5T (4) 1.0T, 50A/m and 1.5T → ˆi+ˆj

Q13.An electron gun is placed inside a long solenoid of radius R on its axis. The solenoid has n turns/length and carries a current I. The electron gun shoots an electron along the radius of the solenoid with speed v. If the electron does not hit the surface of the solenoid, maximum possible value of v is (all symbols have their standard meaning): (1) eμ0nIR (2) eμ0nIR m 2m (3) eμ0nIR (4) 2eμ0nIR 4m m

Q13.Radiation, with wavelength 6561 Å falls on a metal surface to produce photoelectrons. The electrons are made to enter a uniform magnetic field of 3 × 10−4 T . If the radius of the largest circular path followed by the electrons is 10 mm , the work function of the metal is close to: (1) 1.6 eV (2) 0.8eV (3) 1.1 eV (4) 1.8eV

Q13.Consider a circular coil of wire carrying constant current I, forming a magnetic dipole. The magnetic flux through an infinite plane that contains the circular coil and excluding the circular coil area is given by ϕi The magnetic flux through the area of the circular coil area is given by ϕ0 . Which of the following option is correct? (1) ϕi = ϕ0 (2) ϕi > ϕ0 (3) ϕi < ϕ0 (4) ϕi = −ϕ0

Q13.A galvanometer is used in laboratory for detecting the null point in electrical experiments. If, on passing a current of 6mA it produces a deflection of 2° , its figure of merit is close to : (1) 333° A/div (2) 6 × 10−3A/ div (3) 666° A/div. (4) 3 × 10−3A/ div JEE Main 2020 (05 Sep Shift 2) JEE Main Previous Year Paper

Q13.The value of current i1 flowing from A to C in the circuit diagram is : JEE Main 2020 (04 Sep Shift 2) JEE Main Previous Year Paper (1) 5 A (2) 2. 25 A (3) 0. 75 A (4) 1 A

Q13.In the figure shown, the current in the 10 V battery is close to : (1) 0. 71 A from positive to negative terminal (2) 0. 42 A from positive to negative terminal (3) 0. 21 A from positive to negative terminal (4) 0. 36 A from negative to postive terminal

Q13.Two capacitors of capacitances C and 2C are charged to potential differences V and 2V , respectively. These are then connected in parallel in such a manner that the positive terminal of one is connected to the negative terminal of the other. The final energy of this configuration is : (1) 256 CV 2 (2) 32 CV 2 (3) zero (4) 92 CV 2

Q13.A beam of protons with speed 4 × 105 m s−1 enters a uniform magnetic field of 0. 3 T at an angle 60° to the magnetic field, the pitch of the resulting helical path of protons is close to : (Mass of the proton = 1. 67 × 10−27 kg, charge of the proton = 1. 69 × 10−19C) (1) 2 cm (2) 5 cm (3) 12 cm (4) 4 cm

Q13.Which of the following will NOT be observed when a multimeter (operating in resistance measuring mode) probes connected across a component, are just reversed? JEE Main 2020 (03 Sep Shift 2) JEE Main Previous Year Paper (1) Multimeter shows an equal deflection in both (2) Multimeter shows NO deflection in both cases cases i.e., before and after reversing the probes if i.e. before and after reversing the probes if the the chosen component is resistor. chosen component is capacitor (3) Multimeter shows a deflection, accompanied by a (4) Multimeter shows NO deflection in both cases splash of light out of connected component in i.e. before and after reversing the probes is the one direction and NO deflection on reversing the chsosen component is metal wire. probes if the chosen component is LED

Q13.An electron is moving along +x direction with a velocity of 6 × 106 ms−1 . It enters a region of uniform electric field of 300 V /cm pointing along +y direction. The magnitude and direction of the magnetic field set up in this region such that the electron keeps moving along the x direction will be: (1) 3 × 10−4T, along +z direction (2) 5 × 10−3T, along −z direction (3) 5 × 10−3T, along +z direction (4) 3 × 10−4T, along −zdirection JEE Main 2020 (06 Sep Shift 1) JEE Main Previous Year Paper

Q13.A wire carrying current I is bent in the shape ABCDEFA as shown, where rectangle ABCDA and ADEFA are perpendicular to each other. If the sides of the rectangles are of lengths a and b, then the magnitude and direction of magnetic moment of the loop ABCDEFA is : abI along + + ˆk ) (2) ˆk ) (1) √2abI along ( √2ˆj √2 ( √2ˆj √2 + + 2ˆk ) (4) ˆk ) (3) √2abI along ( √5ˆj √5 abI along ( √5ˆj √5

Q13.A galvanometer having a coil resistance 100 Ω gives a full scale deflection when a current of 1mA is passed through it. What is the value of the resistance which can convert this galvanometer into a voltmeter given full scale deflection for a potential difference of 10V? (1) 10kΩ (2) 8.9 kΩ (3) 7.9 kΩ (4) 9.9 kΩ

Q13.The length of a potentiometer wire is 1200 cm and it carries a current of 60 mA For a cell of emf 5 V and internal resistance of 20 Ω the null point on it is found to be at 1000 cm The resistance of whole wire is: (1) 80Ω (2) 120Ω (3) 60Ω (4) 100Ω