Practice Questions

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

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.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

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 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.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

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

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 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.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

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 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.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

Q21.An LCR circuit as shown in the figure is connected to a voltage source Vac whose frequency can be varied. The frequency, at which the voltage across the resistor is maximum, is : (1) 902 Hz (2) 143 Hz (3) 23 Hz (4) 345 Hz

Q22.In a series L −C −R circuit, C = 10−11 Farad, L = 10−5 Henry and R = 100Ohm, when a constant D.C. voltage E is applied to the circuit, the capacitor acquires a charge 10−9 C. The D.C. source is replaced by a sinusoidal voltage source in which the peak voltage E0 is equal to the constant D.C. voltage E. At resonance the peak value of the charge acquired by the capacitor will be : JEE Main 2013 (22 Apr Online) JEE Main Previous Year Paper (1) 10−15C (2) 10−6C (3) 10−10C (4) 10−8C

Q22.A printed page is pressed by a glass of water. The refractive index of the glass and water is 1.5 and 1.33 , respectively. If the thickness of the bottom of glass is 1 cm and depth of water is 5 cm, how much the page will appear to be shifted if viewed from the top ? (1) 1.033 cm (2) 3.581 cm (3) 1.3533 cm (4) 1.90 cm

Q22.In the circuit shown here, the voltage across E and C are respectively 300 V and 400 V . The voltage E of the ac source is : (1) 400 Volt (2) 500 Volt (3) 100 Volt (4) 700 Volt

Q23.This question has Statement-1 and Statement-2. Of the four choices given after the Statements, choose the one that best describes the two Statements. Statement 1: Very large size telescopes are reflecting telescopes instead of refracting telescopes. Statement 2: It is easier to provide mechanical support to large size mirrors than large size lenses. JEE Main 2013 (23 Apr Online) JEE Main Previous Year Paper (1) Statement-1 is true and Statement-2 is false. (2) Statement-1 is false and Statement-2 is true. (3) Statement-1 and statement-2 are true and (4) Statements-1 and statement-2 are true and Statement-2 is correct explanation for statement- Statement-2 is not the correct explanation for 1. statement-1.

Q23.A plane electromagnetic wave in a non-magnetic dielectric medium is given by →E = →E0 (4 × 10−7x −50t) with distance being in meter and time in seconds. The dielectric constant of the medium is : (1) 2.4 (2) 5.8 (3) 8.2 (4) 4.8

Q24.The source that illuminates the double − slit in 'double - slit interference experiment' emits two distinct monochromatic waves of wavelength 500 nm and 600 nm , each of them producing its own pattern on the screen. At the central point of the pattern when path difference is zero, maxima of both the patterns coincide and the resulting interference pattern is most distinct at the region of zero path difference. But as one moves out of this central region, the two fringe systems are gradually out of step such that maximum due to on wavelength coincides with the minimum due to the other and the combined fringe system becomes completely indistinct. This may happen when path difference in nm is: (1) 2000 (2) 3000 (3) 1000 (4) 1500

Q24.Light is incident from a medium into air at two possible angles of incidence (A) 20∘ and (B) 40∘ . In the medium light travels 3.0 cm in 0.2 ns. The ray will : JEE Main 2013 (09 Apr Online) JEE Main Previous Year Paper (1) suffer total internal reflection in both cases (A) (2) suffer total internal reflection in case (B) only and (B) (3) have partial reflection and partial transmission in (4) have 100% transmission in case (A) case (B)

Q24.A light ray falls on a square glass slab as shown in the diagram. The index of refraction of the glass, if total internal reflection is to occur at the vertical face, is equal to : (1) (√2+1) (2) 2 √52 (3) 3 (4) 2 √32

Q24.Diameter of a plano - convex lens is 6 cm and thickness at the centre is 3 mm. If the speed of light in the material of lens is 2 × 108 m s−1 , the focal length of the lens is: (1) 30 cm (2) 10 cm (3) 15 cm (4) 20 cm

Q24.The focal length of the objective and the eyepiece of a telescope are 50 cm and 5 cm respectively. If the telescope is focussed for distinct vision on a scale distant 2 m from its objective, then its magnifying power will be : (1) −4 (2) −8 (3) +8 (4) −2

Q25.This question has Statement-1 and Statements2. Of the four choices given after the Statements, choose the one that best describes the two Statements. Statement-1 : Out of radio waves and microwaves, the radio waves undergo more diffraction. Statement-2 : Radio waves have greater frequency compared to microwaves. (1) Statement-1 is true, Statement-2 is true and (2) Statement-1 is false, Statement-2 is true. Statement-2 is the correct explanation of Statement-1 (3) Statement-1 is true, Statement-2 is false. (4) Statement-1 is true, Statement-2 is true but Statement-2 is not the correct explanation of Statement-1