Physics-DPP-5-Electrostatics

PHYSICS Topic: ELECTROSTATICS Date: 1. Two concentric spheres of radii R and r have similar charges with equal surface densities (σ). What is the electric potential at their common centre ? (a) σ (R – r) ε0 (b) σ (R + r) ε0 (c) Rσ ε0 (d) σr ε0 2. Figure shows three points A, B and C in a region of uniform electric field E . the line AB is perpendicular and BC is parallel to field lines. Then which of the following holds good ? (a) VA = VB = VC (b) VA = VB > VC (c) VA = VB < VC (d) VA > VB = VC (where VA, VB and VC represent the electric potentials at points A, B and C respectively) 3. Two concentric spherical conducting shells of radii r and R (R > r) carry charges q and Q, respectively. The two shells are now connected by a conducting wire. The final charge on the inner shell is : (a) zero (b) (Q + R q)r (c) (Q – q)r qr R (d) R 4. If 1000 small droplets each of charge q and radius r combine to form a big drop, the ratio of potential of big drop to that of small droplet will be : (a) 10 (b) 100 (c) 1000 (d) 10,000 5. Two infinitely long parallel conducting plates having surface charge densities + σ and – σ respectively, are separated by a small distance d. The medium between the plates is vacuum. If ε0 is the dielectric permittivity of vacuum, then the potential difference between the plates is : (a) zero (b) σd V ε0 (c) σd V 2ε0 (d) 2σ d V ε0 6. As per this diagram a point charge +q is placed at the origin O. Work done is taking another point charge – Q from the point a [coordinates (0, a)] to another point B [coordinates (a, 0)] along the straight path AB is : (a) zero (b) æç –qQ ç 1 ö÷ 2 ÷ 2a çè4πε0 a ø÷ (c) æç –qQ 1 ö÷ a 2 ÷ (d) æç qQ ç 1 ö÷ 2 ÷ 4πε0 a ø÷ çè4πε0 a ø÷ 7. Four charges Q, – Q, Q, – Q are placed at the corners of a square as shown and E, F, G & H are mid points . The potential is zero at points : (a) E, F, G, H, O (b) E, O, G only (c) H,O,F only (d) O only PHYSICS Topic: ELECTROSTATICS Date: 8. Three identical metallic uncharged spheres A, B and C of radius a are kept on the corners of an equilateral triangle of side d (d > > a). A fourth sphere (radius a) which has charge Q touches A and is then removed to a position far away. B is earthed and then the earth connection is removed. C is then earthed. The charge on C is : (a) Qa æça – d ö÷ (b) Qa æç2d – a ö÷ (c) Qa æça – d ö÷ (d) 2Qa æçd – a ö÷ 2d 2d ø÷ 2d çè d ø÷ 2d çè d ø÷ d çè 2d ø÷ 9. A charge + Q is uniformly distributed over a thin ring of radius R. A negative point charge – Q and mass m starts from rest at a point far away from the centre of the ring and moves towards the centre. The velocity of this particle at the moment it passes through the centre of the ring is : (a) (b) (c) (d) 10. Equipotential surfaces are shown in figure. Then the electric field strength will be : (a) 100 Vm–1 along X -axis. (b) 100 Vm–1 along Y-axis. (c) 200 Vm–1 at an angle 120o with X-axis (d) 50 Vm–1 at an angle 120o with X-axis PHYSICS Topic: ELECTROSTATICS Date: 1. (b) 2. (b) Answer Key 3. (a) 4. (a) 5. (d) 6. (a) 7. (a) 8. (c) 9. (c) 10. (c)

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