Practice Questions

Q16.A liquid drop having 6 excess electrons is kept stationary under a uniform electric field of 25.5 kVm−1 . The density of liquid is 1.26 × 103 kg m−3 . The radius of the drop is (neglect buoyancy). (1) 4.3 × 10−7 m (2) 7.8 × 10−7 m (3) 0.078 × 10−7 m (4) 3.4 × 10−7 m

Q17.This question has Statement I and Statement II. Of the four choices given after the Statements, choose the one that best describes the two Statements. Statement - I : Higher the range, greater is the resistance of ammeter. Statement - II : To increase the range of ammeter, additional shunt needs to be used across it. (1) Statement- I is true, Statement- II is false. (2) Statement- I is false, Statement- II is true. (3) Statement- I is true, Statement- II is true, (4) Statement- I is true, Statement- II is true, Statement- II is the correct explanation of Statement- II is not the correct explanation of Statement- I. Statement- I.

Q17.A dc source of emf E1 = 100 V and internal resistance r = 0.5Ω, a storage battery of emf E2 = 90 V and an external resistance R are connected as shown in figure. For what value of R no current will pass through the JEE Main 2013 (22 Apr Online) JEE Main Previous Year Paper battery? (1) 5.5Ω (2) 3.5Ω (3) 4.5Ω (4) 2.5Ω

Q17.The earth's magnetic field lines resemble that of a dipole at the centre of the earth. If the magnetic moment of this dipole is close to 8 × 1022Am2 , the value of earth's magnetic field near the equator is close to (radius of the earth = 6.4 × 106 m) (1) 0.6 Gauss (2) 1.2 Gauss (3) 1.8 Gauss (4) 0.32 Gauss

Q17.A parallel plate capacitor of area 60 cm2 and separation 3 mm is charged initially to 90μC. If the medium between the plate gets slightly conducting and the plate loses the charge initially at the rate of 2.5 × 10−8C/s, then what is the magnetic field between the plates ? (1) 2.5 × 10−8 T (2) 2.0 × 10−7 T (3) 1.63 × 10−11 T (4) Zero

Q17.A letter ′A′ is constructed of a uniform wire with resistance 1.0Ω per cm, The sides of the letter are 20 cm and the cross piece in the middle is 10 cm long. The apex angle is 60 . The resistance between the ends of the legs is close to: (1) 50.0Ω (2) 10Ω (3) 36.7Ω (4) 26.7Ω

Q18.One of the two small circular coils, (none of them having any self - inductance) is suspended with a V-shaped copper wire, with plane horizontal. The other coil is placed just below the first one with plane horizontal. Both the coils are connected in series with a dc supply. The coils are found to attract each other with a force. Which one of the following statements is incorrect? (1) Both the coils carry currents in the same (2) Coils will attract each other, even if the supply is direction. an ac source. (3) Force is proportional to d−1 (4) Force is proportional to d−2

Q18.Two short bar magnets of length 1 cm each have magnetic moments 1 .20 A m2 and 1 .00 A m2 respectively. They are placed on a horizontal table parallel to each other with their N poles pointing towards the south. They have a common magnetic equator and are separated by a distance of 20 .0 cm. The value of the resultant horizontal magnetic induction at the mid-point O of the line joining their centres is close to ( Horizontal component of earth's magnetic induction is 3 .6 ×10−5 Wb m−2 ) (1) 3 .50 ×10−4 Wb m−2 (2) 5 .80 ×10−4 Wb m−2 (3) 3 .6 ×10−5 Wb m−2 (4) 2 .56 ×10−4 Wb m−2

Q18.A shunt of resistance 1 Ω is connected across a galvanometer of 120 Ω resistance. A current of 5.5 ampere gives full scale deflection in the galvanometer. The current that will give full scale deflection in the absence of the shunt is nearly : (1) 5.5 ampere (2) 0.5 ampere (3) 0.004 ampere (4) 0.045 ampere

Q18.Which of the four resistances P, Q, R and S generate the greatest amount of heat when a current flows from A to B ? (1) Q (2) S (3) P (4) R

Q18.To find the resistance of a galvanometer by the half deflection method the following circuit is used with resistances R1 = 9970 W, R2 = 30 W and R3 = 0 . The deflection in the galvanometer is d. With R3 = 107 W the deflection changed to d2 . The galvanometer resistance is approximately: (1) 107Ω (2) 137Ω (3) 107/2Ω (4) 77Ω

Q19.A metal sample carrying a current along X− axis with density Jx is subjected to a magnetic field Bz (along z− axis). The electric field Ey developed along Y-axis is directly proportional to Jx as well as Bz . The constant of proportionality has SI unit. (1) m2 (2) m3 A As (3) m2 (4) As As m3

Q19.A metallic rod of length l is tied to a string of length 2l and made to rotate with angular speed ω on a horizontal table with one end of the string fixed. If there is a vertical magnetic field B in the region, the e.m.f. induced across the ends of the rod is: (1) 4Bωl2 (2) 5Bωl2 2 2 (3) 2Bωl2 (4) 3Bωl2 2 2

Q19.A rectangular loop of wire, supporting a mass m, hangs with one end in a uniform magnetic field →B pointing out of the plane of the paper. A clockwise current is set up such that i > mg/Ba, where a is the width of the JEE Main 2013 (23 Apr Online) JEE Main Previous Year Paper loop. Then : (1) The weight rises due to a vertical force caused by (2) The weight do not rise due to vertical for caused the magnetic field and work is done on the by the magnetic field and work is done on the system. system. (3) The weight rises due to a vertical force caused by (4) The weight rises due to a vertical force caused by the magnetic field but no work is done on the the magnetic field and work is extracted from the system. magnetic field.

Q19.Choose the correct sketch of the magnetic field lines of a circular current loop shown by the dot and the cross ⊗. JEE Main 2013 (22 Apr Online) JEE Main Previous Year Paper (1) (2) (3) (4)

Q19.A uniform electric field →E exists between the plates of a charged condenser. A charged particle enters the space between the plates and perpendicular to →E . The path of the particle between the plates is a: JEE Main 2013 (09 Apr Online) JEE Main Previous Year Paper (1) straight line (2) hyperbola (3) parabola (4) circle

Q20.When resonance is produced in a series LCR circuit, then which of the following is not correct? (1) Current in the circuit is in phase with the applied (2) Inductive and capacitive reactances are equal. voltage. (3) If R is reduced, the voltage across capacitor will (4) Impedance of the circuit is maximum. increase.

Q20.A circular loop of radius 0. 3 cm lies parallel to a much bigger circular loop of radius 20 cm. The centre of the small loop is on the axis of the bigger loop. The distance between their centres is 15 cm. If a current of 2. 0 A flows through the smaller loop, then the flux linked with a bigger loop is: (1) 3 .3 ×10−11 weber (2) 6 .6 ×10−9 weber (3) 9 .1 ×10−11 weber (4) 6 × 10−11 weber

Q20.A particle of charge 16 × 10−16C moving with velocity 10 ms−1 along x-axis enters a region where magnetic field of induction →B is along the y-axis and an electric field of magnitude 104Vm−1 is along the negative z- axis. If the charged particle continues moving along x-axis, the magnitude of →B is : (1) 16 × 103 Wb m−2 (2) 2 × 103 Wb m−2 (3) 1 × 103 Wb m−2 (4) 4 × 103 Wb m−2

Q20.A current i is flowing in a straight conductor of length L. The magnetic induction at a point on its axis at a distance L from its centre will be : 4 (1) Zero (2) μ0i 2πL (3) μ0i (4) 4μ0i √2L √5πL

Q20.An electric current is flowing through a circular coil of radius R. The ratio of the magnetic field at the centre of the coil and that at a distance 2√2R from the centre of the coil and on its axis is : (1) 2√2 (2) 27 (3) 36 (4) 8

Q21.The plot given below is of the average power delivered to an LRC circuit versus frequency. The quality factor of the circuit is : (1) 5.0 (2) 2.0 (3) 2.5 (4) 0.4

Q21.A series LR circuit is connected to an ac source of frequency ω and the inductive reactance is equal to 2R. A capacitance of capacitive reactance equal to R is added in series with L and R. The ratio of the new power factor to the old one is : JEE Main 2013 (25 Apr Online) JEE Main Previous Year Paper (1) (2) 3 5 √2 √2 (3) (4) 2 2 √3 √5

Q21.The amplitude of a damped oscillator decreases to 0.9 times its original magnitude in 5s. In another 10s it will decrease to α times its original magnitude, where α equals : JEE Main 2013 (07 Apr) JEE Main Previous Year Paper (1) 0.729 (2) 0.6 (3) 0.7 (4) 0.81

Q21.Two coils, X and Y, are kept in close vicinity of each other. When a varying current, I(t), flows through coil X , the induced emf(V (t)) in coil Y, varies in the manner shown here. The variation of I(t), with time, can then be represented by the graph labelled as graph : (A) (B) JEE Main 2013 (09 Apr Online) JEE Main Previous Year Paper (C) (D) (1) A (2) C (3) B (4) D