Practice Questions

Q42.Three charges −q1, +q2 and −q3 are placed as shown in the figure. The x-component of the force on −q1 is proportional to (1) q2 −q3 cos θ (2) q2 + q3 sin θ b2 a2 b2 a2 (3) q2 + q3 cos θ (4) q2 −q3 sin θ b2 a2 b2 a2

Q43.A sheet of aluminium foil of negligible thickness is introduced between the plates of a capacitor. The capacitance of the capacitor (1) decreases (2) remains unchanged (3) becomes infinite (4) increases

Q44.The work done in placing a charge of 8 × 10−18 coulomb on a condenser of capacity 100 micro-farad is (1) 16 × 10−32 joule (2) 3.1 × 10−26 joule (3) 4 × 10−10 joule (4) 32 × 10−32 joule

Q45.The length of a wire of a potentiometer is 100 cm, and the e.m.f. of its standard cell is E volt. It is employed to measure the e.m.f of a battery whose internal resistance is 0.5Ω. If the balance point is obtained at l = 30 cm from the positive end, the e.m.f. of the battery is (1) 30E (2) 30E 100.5 (100−0.5) (3) 30(E−0.5i) , where i is the current in the (4) 30E100 100 potentiometer wire

Q46.A strip of copper and another of germanium are cooled from room temperature to 80 K. The resistance of (1) each of these decreases (2) copper strip increases and that of germanium decreases (3) copper strip decreases and that of germanium (4) each of these increases increases

Q47.The thermo e.m.f. of a thermo-couple is 25μV/∘C at room temperature. A galvanometer of 40 ohm resistance, capable of detecting current as low as 10−5 A, is connected with the thermo couple. The smallest temperature JEE Main 2003 JEE Main Previous Year Paper difference that can be detected by this sytem is (1) 16∘C (2) 12∘C (3) 80C (4) 20∘C

Q48.The negative Zn pole of a Daniell cell, sending a constant current through a circuit, decreases in mass by 0.13 g in 30 minutes. If the electrochemical equivalent of Zn and Cu are 32.5 and 31.5 respectively, the increase in the mass of the positive Cu pole in this time is (1) 0.180 g (2) 0.141 g (3) 0.126 g (4) 0.242 g

Q49.An ammeter reads up to 1 ampere. Its internal resistance is 0.81ohm. To increase the range to 10 A the value of the required shunt is (1) 0.03Ω (2) 0.3Ω (3) 0.9Ω (4) 0.09Ω

Q50.A 3 volt battery with negligible internal resistance is connected in a circuit as shown in the figure. The current I, in the circuit will be (1) 1 A (2) 1.5 A (3) 2 A (4) 1/3 A

Q51.A 220 volt, 1000 watt bulb is connected across a 110 volt mains supply. The power consumed will be (1) 750watt (2) 500watt (3) 250watt (4) 1000watt

Q52.The length of a given cylindrical wire is increased by 100%. Due to the consequent decrease in diameter the change in the resistance of the wire will be (1) 200% (2) 100% (3) 50% (4) 300%

Q53.A thin rectangular magnet suspended freely has a period of oscillation equal to T . Now it is broken into two equal halves (each having half of the original length) and one piece is made to oscillate freely in the same field. If its period of oscillation is T ′ , the ratio TT ′ is (1) 1 (2) 1 2√2 2 (3) 2 (4) 1 4

Q54.A magnetic needle lying parallel to a magnetic field requires W units of work to turn it through 60∘ . The torque needed to maintain the needle in this position will be (1) √3 W (2) W (3) √3 2 W (4) 2 W JEE Main 2003 JEE Main Previous Year Paper

Q55.The magnetic lines of force inside a bar magnet (1) are from north-pole to south-pole of the magnet (2) do not exist (3) depend upon the area of cross-section of the bar (4) are from south-pole to north-pole of the magnet magnet

Q56.Curie temperature is the temperature above which (1) a ferromagnetic material becomes paramagnetic (2) a paramagnetic material becomes diamagnetic (3) a ferromagnetic material becomes diamagnetic (4) a paramagnetic material becomes ferromagnetic

Q57.A particle of mass M and charge Q moving with velocity →v describe a circular path of radius R when subjected to a uniform transverse magnetic field of induction B. The work done by the field when the particle completes one full circle is (1) ( Mv2R )2πR (2) Zero (3) BQ2πR (4) BQ v 2πR

Q58.A particle of charge −16 × 10−18 coulomb moving with velocity 10 ms−1 along the x-axis enters a region where a magnetic field of induction B is along the y-axis, and an electric field of magnitude 104 V/m is along the negative z-axis. If the charged particle continues moving along the x-axis, the magnitude of B is (1) 103 Wb/m2 (2) 105 Wb/m2 (3) 1016 Wb/m2 (4) 10−3 Wb/m2

Q59.Two coils are placed close to each other. The mutual inductance of the pair of coils depends upon (1) the rates at which currents are changing in the (2) relative position and orientation of the two coils two coils (3) the materials of the wires of the coils. (4) the currents in the two coils

Q60.When the current changes from +2 A to −2 A in 0.05 second, an e.m.f. of 8 V is induced in a coil. The coefficient of self-induction of the coil is (1) 0.2H (2) 0.4H (3) 0.8H (4) 0.1H

Q61.In an oscillating LC circuit the maximum charge on the capacitor is Q. The charge on the capacitor when the energy is stored equally between the electric and magnetic field is (1) Q (2) Q 2 √3 (3) Q (4) Q √2

Q62.The core of any transformer is laminated so as to (1) reduce the energy loss due to eddy currents (2) make it light weight (3) make it robust and strong (4) increase the secondary voltage

Q63.A metal wire of linear mass density of 9.8 g/m is stretched with a tension of 10 kg-wt between two rigid supports 1 metre apart. The wire passes at its middle point between the poles of a permanent magnet, and it vibrates in resonance when carrying an alternating current of frequency n. The frequency n of the alternating source is JEE Main 2003 JEE Main Previous Year Paper (1) 50 Hz (2) 100 Hz (3) 200 Hz (4) 25 Hz

Q64.The image formed by an objective of a compound microscope is (1) virtual and diminished (2) real and diminished (3) real and enlarged (4) virtual and enlarged

Q65.To get three images of a single object, one should have two plane mirrors at an angle of (1) 60∘ (2) 90∘ (3) 120∘ (4) 30∘

Q66.To demonstrate the phenomenon of interference, we require two sources which emit radiation (1) of nearly the same frequency (2) of the same frequency (3) of different wavelengths (4) of the same frequency and having a definite phase relationship