Practice Questions

Q21.Charges are placed on the vertices of a square as shown. Let E be the electric field and V the potential at the centre. If the charges on A and B are interchanged with those on D and C respectively, then JEE Main 2007 JEE Main Previous Year Paper (1) →E remains unchanged, V changes (2) Both →E and V change (3) →E and V remains unchanged (4) →E changes, V remains unchanged

Q22.The potential at a point x (measured in μm ) due to some charges situated on the x-axis is given by V(x) = 20/ (x2 −4) Volts. The electric field E at x = 4 μm is given by (1) 5/3 Volt/ μm and in the −ve x direction (2) 5/3 Volt/ μm and in the +ve x direction. (3) 10/9 Volt/μm and in the −ve x direction (4) 10/9 Volt/μm and in the +ve x direction.

Q23.If gE and gm are the accelerations due to gravity on the surfaces of the earth and the moon respectively and if Millikan's oil drop experiment could be performed on the two surfaces, one will find the ratio electronic charge on the moon to be electronic charge on the earth (1) 1 (2) 0 (3) gE/gm (4) gm / gE

Q24.A battery is used to charge a parallel plate capacitor till the potential difference between the plates becomes equal to the electromotive force of the battery. The ratio of the energy stored in the capacitor and the work done by the battery will be (1) 1 (2) 2 (3) 1 (4) 1 4 2

Q25.A parallel plate condenser with a dielectric of dielectric constant K between the plates has a capacity C and is charged to a potential V volts. The dielectric slab is slowly removed from between the plates and then reinserted. The net work done by the system in this process is (1) 1/2( K −1)CV2 (2) CV2( K −1)/K (3) (K −1)CV2 (4) zero

Q26.The resistance of a wire is 5 ohm at 50∘C and 6 ohm at 100∘C. The resistance of the wire at 0∘C will be (1) 2 ohm (2) 1 ohm (3) 4 ohm (4) 3 ohm

Q27.A long straight wire of radius ' a ' caries a steady current i. The current is uniformly distributed across its cross section. The ratio of the magnetic field at a and 2a is 2 (1) 1 (2) 4 4 (3) 1 (4) 12

Q28.A current I flows along the length of an infinitely long, straight, thin walled pipe. Then JEE Main 2007 JEE Main Previous Year Paper (1) the magnetic field is zero only on the axis of the (2) the magnetic field is different at different points pipe inside the pipe (3) the magnetic field at any point inside the pipe is (4) the magnetic field at all points inside the pipe is zero the same, but not zero

Q29.A charged particle with charge q enters a region of constant, uniform and mutually orthogonal fields →E and →B with a velocity →v perpendicular to both →E and →B, and comes out without any change in magnitude or direction of →v. Then (1) →v = →E × →B/B2 (2) →v = →B × →E/B2 → → (3) →v = →E × →B/E2 (4) →v = B × E/E2

Q30.A charged particle moves through a magnetic field perpendicular to its direction. Then (1) the momentum changes but the kinetic energy is (2) both momentum and kinetic energy of the constant particle are not constant (3) both, momentum and kinetic energy of the (4) kinetic energy changes but the momentum is particle are constant constant

Q31.Two identical conducting wires AOB and COD are placed at right angles to each other. The wire AOB carries an electric current I1 and COD carries a current I2 . The magnetic field on a point lying at a distance ' d ' from O, in a direction perpendicular to the plane of the wires AOB and COD, will be given by (1) μ0 I1+I2 1/2 (2) μ0 2πd (I21 + I22)1/2 2π ( d ) (3) 2πd μ0 (I1 + I2) (4) 2πdμ0 (I21 + I22)

Q32.An ideal coil of 10H is connected in series with a resistance of 5Ω and a battery of 5 V . 2 second after the connection is made the current flowing in amperes in the circuit is (1) (1 −e) (2) e (3) e−1 (4) (1 −e−1)

Q33.In an a.c. circuit the voltage applied is E = E0 sin ωt. The resulting current in the circuit is I = I0 sin (ωt −π2 ). The power consumption in the circuit is given by (1) P = E0I0 (2) P = zero √2 (3) P = E0I02 (4) P√2E0I0

Q34.Two lenses of power −15 D and +5 D are in contact with each other. The focal length of the combination is (1) −20 cm (2) −10 cm (3) +20 cm (4) +10 cm

Q35.In a Young's double slit experiment the intensity at a point where the path difference is λ ( λ being the 6 wavelength of the light used) is I. If I0 denotes the maximum intensity, I0I is equal to (1) 1 (2) √3 √2 2 (3) 1/2 (4) 3/4

Q36.Photon of frequency v has a momentum associated with it. If c is the velocity of light, the momentum is JEE Main 2007 JEE Main Previous Year Paper (1) v/c (2) hvc (3) hv/c2 (4) hv/c

Q37.Which of the following transitions in hydrogen atoms emit photons of highest frequency? (1) n = 2 to n = 6 (2) n = 6 to n = 2 (3) n = 2 to n = 1 (4) n = 1 to n = 2

Q38.If Mo is the mass of an oxygen isotope 8O17, Mp and MN are the masses of a proton and a neutron respectively, the nuclear binding energy of the isotope is (1) (Mo −8Mp)C2 (2) (Mo −8Mp −9MN)C2 (3) MoC2 (4) (Mo −17MN)C2

Q40.The half-life period of a radio-active element X is same as the mean life time of another radioactive element Y . Initially they have the same number of atoms. Then (1) X will decay faster than Y (2) Y will decay faster than X (3) X and Y have same decay rate initially (4) X and Y decay at same rate always.

Q1. Which of the following units denotes the dimensions ML2/Q2 , where Q denotes the electric charge? (1) Weber (Wb) (2) Wb/m2 (3) Henry (H) (4) H/m2

Q2. A particle located at x = 0 at time t = 0 , starts moving along the positive x-direction with a velocity ' v ' that varies as v = α√x. The displacement of the particle varies with time as (1) t3 (2) t2 (3) t (4) t1/2

Q3. A body falling from rest under gravity passes a certain point P . It was at a distance of 400 m from P, 4 s prior to passing through P . If g = 10 m/s2 , then the height above the point P from where the body began to fall is (1) 720 m (2) 900 m (3) 320 m (4) 680 m

Q4. A mass of Mkg is suspended by a weightless string. The horizontal force that is required to displace it until the string makes an angle of 45∘ with the initial vertical direction is (1) Mg(√2 −1) (2) Mg(√2 + 1) (3) Mg√2 (4) Mg √2

Q5. A player caught a cricket ball of mass 150 g moving at a rate of 20 m/s. If the catching process is completed in 0.1 s, the force of the blow exerted by the ball on the hand of the player is equal to (1) 300 N (2) 150 N (3) 3 N (4) 30 N

Q6. A particle of mass 100 g is thrown vertically upwards with a speed of 5 m/s. the work done by the force of gravity during the time the particle goes up is (1) 0.5 J (2) −0.5 J (3) −1.25 J (4) 1.25 J