Practice Questions

Q10.Angular momentum of the particle rotating with a central force is constant due to (1) Constant Force (2) Constant linear momentum. (3) Zero Torque (4) Constant Torque

Q11.One end of a thermally insulated rod is kept at a temperature T1 and the other at T2 . The rod is composed of two sections of lengths ℓ1 and ℓ2 and thermal conductivities k1 and k2 respectively. The temperature at the interface of the two sections is (1) (k2ℓ2T1 + k1ℓ1T2)/ (k1ℓ1 + k2ℓ2) (2) (k2ℓ1T1 + k1ℓ1T2)/ (k2ℓ1 + k1ℓ2) (3) (k1ℓ2T1 + k2ℓ1T2)/ (k1ℓ2 + k2ℓ1) (4) (k1ℓ1T1 + k2ℓ2T2)/ (k1ℓ1 + k2ℓ2)

Q12.A Carnot engine, having an efficiency of η = 1/10 as heat engine, is used as a refrigerator. If the work done on the system is 10 J, the amount of energy absorbed from the reservoir at lower temperature is (1) 99 J (2) 90 J (3) 1 J (4) 100 J

Q13.When a system is taken from state i to state f along the path iaf , it is found that Q = 50 cal and W = 20 cal. Along the path' ibf Q = 36 cal. W along the path ibf is (1) 6 cal (2) 16 cal. (3) 66 cal. (4) 14 cal. JEE Main 2007 JEE Main Previous Year Paper

Q14.If Cp and Cv denote the specific heats of nitrogen per unit mass at constant pressure and constant volume respectively, then (1) Cp −Cv = R/28 (2) Cp −Cv = R/14 (3) Cp −Cv = R (4) Cp −Cv = 28R

Q15.The displacement of an object attached to a spring and executing simple harmonic motion is given by x = 2 × 10−2 cos πt metres. The time at which the maximum speed first occurs is (1) 0.5 s (2) 0.75 s (3) 0.125 s (4) 0.25 s

Q16.A point mass oscillates along the x-axis according to the law x = x0 cos(ωt −π/4). If the acceleration of the particle is written as a = A cos(ωt + δ) (1) A = x0, δ = −π/4 (2) A = x0ω2, δ = −π/4 (3) A = x0ω2, δ = −π/4 (4) A = x0ω2, δ = 3π/4

Q17.Two springs, of force constants k1 and k2 , are connected to a mass m as shown. The frequency of oscillation of the mass is f . If both k1 and k2 are made four times their original values, the frequency of oscillation becomes (1) f/2 (2) f/4 (3) 4f (4) 2f

Q18.A particle of mass m executes simple harmonic motion with amplitude ' a ' and frequency ' v '. The average kinetic energy during its motion from the position of equilibrium to the end is (1) π2ma2v2 (2) 41 π2ma2v2 (3) 4π2ma2v2 (4) 2π2ma2v2

Q19.A sound absorber attenuates the sound level by 20 dB . The intensity decreases by a factor of (1) 1000 (2) 10000 (3) 10 (4) 100

Q20.An electric charge 10−3μC is placed at the origin (0, 0) of X −Y co-ordinate system. Two points A and B are situated at (√2, √2) and (2, 0) respectively. The potential difference between the points A and B will be (1) 9 volt (2) zero (3) 2 volt (4) 4.5 volt

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