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)

Comments

Post a Comment

Popular posts from this blog

PHYSICS-15-10- 11th (PQRS) SOLUTION

XI (PQRS) PHYSICS REVIEW TEST-5 Select the correct alternative. (Only one is correct) [15 × 3 = 45] There is NEGATIVE marking. 1 mark will be deducted for each wrong answer. Q.31 Two trains, which are moving along different tracks in opposite directions towards each other, are put on the same track due to a mistake. Their drivers, on noticing the mistake, start slowing down the trains when the trains are 300 m apart. Graphs given below show their velocities as function of time as the trains slow down. The separation between the trains when both have stopped, is: (A) 120 m (B) 280 m (C) 60 m (D*) 20 m 1 [Sol: x1 = 2 1 × 10 × 40 = 200 m; x2 = – 2 × 8 × 20 = –80 m  xreletive = x1 + x2 = 280  separation = 300 – 280 = 20 m (D) ] Q.32 One end of a thin uniform rod of length L and mass M is riveted to the centre of a uniform circular disc of radius r and mass 2 M so that the rod is normal to the disc. The centre of mass of the combination from the centre of the disc is at dist
Read more

8-Circular Motion

8.1 (D) The maximum angular speed of the hoop corresponds to the situation when the bead is just about to slide upwards. The free body diagram of the bead is For the bead not to slide upwards. m2 (r sin 45°) cos 45° – mg sin 45° < N (1) where N = mg cos 45° + m2 (r sin 45º) sin 45° (2) From 1 and 2 we get.  = rad / s. 8.2 (C) Let v be the speed of particle at B, just when it is about to loose contact. From application of Newton's second law to the particle normal to the spherical surface. mv2 = mg sin  (1) r Applying conservation of energy as the block moves from A to B.. 1 mv2 = mg (r cos  – r sin ) (2) 2 Solving 1 and 2 we get 3 sin  = 2 cos  8.3 (A) As the mass is at the verge of slipping ∴ mg sin37 –  mg cos37 = m2r 6 – 8 = 4.5   = 3 16 8.4 (B) As when they collide vt  1  72v 2  2 2  25R   R = vt  t =   5R 6v Now angle covered by A =   vt R 11 Put t  angle covered by A = 6 8.5 (C) The acceleration vector s
Read more

4. THEORY-Current Electrictricity

CURRENT ELECTRICITY  1 . ELECTRIC CURRENT (a) Time rate of flow of charge through a cross sectional area is called Current. if q charge flows in time interval t then average current is given by q Iav = t and Instantaneous current i =. lim q  dq t0 t dt (b) Direction of current is along the direction of flow of positive charge or opposite to the direction of flow of negative charge. But the current is a scalar quantity. i i q+ velocity q– velocity SI unit of current is ampere and 1 Ampere = 1 coloumb/sec 1 coloumb/sec = 1A 2 . CONDUCTOR In some materials, the outer electrons of each atom or molecule are only weakly bound to it. These electrons are almost free to move throughout the body of the material and are called free electrons. They are also known as conduction electrons. When such a material is placed in an electric field, the free electrons drift in a direction opposite to the field. Such materials are called conductors. 3 . INSULATOR Another class o
Read more