Practice Questions

Q39.The displacement y of a particle in a medium can be expressed as y = 10−6 sin(110t + 20x + π/4)m, where t is in seconds and x in meter. The speed of the wave is JEE Main 2004 JEE Main Previous Year Paper (1) 2000 m/s (2) 5 m/s (3) 20 m/s (4) 5πm/s

Q40.Two spherical conductor B and C having equal radii and carrying equal charges in them repel each other with a force F when kept apart at some distance. A third spherical conductor having same radius as that of B but uncharged brought in contact with B, then brought in contact with C and finally removed away from both. The new force of repulsion, between B and C is (1) F/4 (2) 3F/4 (3) F/8 (4) 3 F/8 .

Q41.A charged particle q is shot towards another charged particle Q which is fixed, with a speed v it approaches Q upto a closest distance r and then returns. If q were given a speed 2v, the closest distances of approach would be (1) r (2) 2r (3) r/2 (4) r/4

Q42.Four charges equal to −Q are placed at the four corners of a square and a charge q is at its centre. If the system is in equilibrium the value of q is (1) −Q4 (1 + 2√2) (2) −Q2 (1 + 2√2) (3) −Q2 (1 + 2√2) (4) Q2 (1 + 2√2)

Q43.A charged oil drop is suspended in a uniform field of 3 × 104 V/m so that it neither falls nor rises. The charge on the drop will be (take the mass of the charge = 9.9 × 10−15 kg and g = 10 m/s2 ) (1) 3.3 × 10−18C (2) 3.2 × 10−18C (3) 1.6 × 10−18C (4) 4.8 × 10−18C

Q44.An α-particle of energy 5MeV is scattered through 180∘ by a fixed uranium nucleus. The distance of the closest approach is of the order of (1) 1Å (2) 10−10 cm (3) 10−12 cm (4) 10−15 cm

Q45. The total current supplied to the circuit by the battery is (1) 1 A (2) 2 A (3) 4A (4) 6 A

Q46.The resistance of the series combination of two resistances is S . When they are joined in parallel through total resistance is P . If S = nP , then the minimum possible value of n is JEE Main 2004 JEE Main Previous Year Paper (1) 4 (2) 3 (3) 2 (4) 1

Q47.An electric current is passed through a circuit containing two wires of the same material, connected in parallel. If the length and radii of the wires are in the ratio of 4/3 and 2/3 , then the ratio of the currents passing through the wire will be (1) 3 (2) 1/3 (3) 8/9 (4) 2

Q48.In a metre bridge experiment null point is obtained at 20 cm from one end of the wire when resistance X is balanced against another resistance Y . If X < Y , then where will be the new position of the null point from the same end, if one decides to balance a resistance of 4X against Y? (1) 50 cm (2) 80 cm (3) 40 cm (4) 70 cm

Q49.The electrochemical equivalent of a metal is 3.3 × 10−7 kg per coulomb. The mass of the metal liberated at the cathode when a 3 A current is passed for 2 seconds will be (1) 19.8 × 10−7 kg (2) 9.9 × 10−7 kg (3) 6.6 × 10−7 kg (4) 1.1 × 10−7 kg

Q50.A piece of copper and another of germanium are cooled from room temperature to 77 K, the resistance of (1) each of them increases (2) each of them decreases (3) copper decreases and germanium increases (4) copper increases and germanium decreases

Q51.The length of a magnet is large compared to its width and breadth. The time period of its width and breadth. The time period of its oscillation in a vibration magnetometer is 2 s. The magnet is cut along its length into three equal parts and three parts are then placed on each other with their like poles together. The time period of this combination will be (1) 2 s (2) 2/3 s (3) 2√3 s (4) 2/√3 s

Q52.The materials suitable for making electromagnets should have (1) high retentivity and high coercivity (2) low retentivity and low coercivity (3) high retentivity and low coercivity (4) low retentivity and high coercivity

Q53.A current I ampere flows along an infinitely long straight thin-walled tube, then the magnetic induction at any point inside the tube is (1) infinite (2) zero μ0 2i (3) tesla (4) 2n2 B r 4π

Q54.A long wire carries a steady current. It is bent into a circle of one turn and the magnetic field at the centre of the coil is B. It is then bent into a circular loop of n turns. The magnetic field at the centre of the coil will be (1) nB (2) n2 B (3) 2nB (4) 2n2B JEE Main 2004 JEE Main Previous Year Paper

Q55.The magnetic field due to a current carrying circular loop of radius 3 cm at a point on the axis at a distance of 4 cm from the centre is 54μT. What will be its value at the centre of the Loop? (1) 250μT (2) 150μT (3) 125μT (4) 75μT

Q56.Two long conductors, separated by a distance d carry current I1 and I2 in the same direction. They exert a force F on each other. Now the current in one of them increased to two times and its direction reversed. The distance is also increased to 3 d . The new value of the force between them is (1) −2 F (2) F/3 (3) −2F/3 (4) −F/3

Q57.A coil having n turns and resistance 4RΩ. This combination is moved in time t seconds from a magnetic field W1 weber to W2 weber. The induced current in the circuit is (1) −W2−W15Rnt (2) −(W2−W1)5Rt (3) −W2−W1Rnt (4) −n(W2−W1)Rt

Q58.In a uniform magnetic field of induction B a wire in the form of semicircle of radius r rotates about the diameter of the circle with angular frequency ω. The axis of rotation is perpendicular to the field. If the total resistance of the circuit is R the mean power generated per period of rotation is (1) Bπr2ω (2) (Bπr2ω)2 2R 2R (3) (Bπrω)2 (4) (Bπrω2)2 2R 8R

Q59.A metal conductor of length 1 m rotates vertically about one of its ends at angular velocity 5 radians per second. If the horizontal component of earth's magnetic field is 0.3 × 10−4 T, then the e.m.f. developed between the two ends of the conductor is (1) depends on the nature of the metal used (2) depends on the intensity of the radiation (3) depends both on the intensity of the radiation and (4) is the same for all metals and independent of the the metal used intensity of the radiation.

Q60.Alternating current can not be measured by D.C. ammeter because (1) A.C. cannot pass through D.C. (2) A.C. changes direction (3) average value of current for complete cycle is (4) D.C. ammeter will get damaged. zero

Q61.In an LCR series a.c. circuit, the voltage across each of the components, L, C and R is 50 V . The voltage across the LC combination will be (1) 50 V (2) 50√2 V (3) 100 V (4) 0 V (zero)

Q62.In a LCR circuit capacitance is changed from C to 2C . For the resonant frequency to remain unchanged, the inductance should be changed from L to (1) 4 L (2) 2 L (3) L/2 (4) L/4 JEE Main 2004 JEE Main Previous Year Paper

Q63.An electromagnetic wave of frequency v = 3.0MHz passes from vacuum into a dielectric medium with permittivity ε = 4.0 . Then (1) wavelength is doubled and the frequency remains (2) wavelength is doubled and frequency becomes unchanged half (3) wavelength is halved and frequency remains (4) wavelength and frequency both remain unchanged unchanged.