Electrostat-05-SUBJECTIVE LEVEL - I (C.B.S.E.)

SUBJECTIVE LEVEL - I (C.B.S.E.) (REVIEW YOUR CONCEPTS) 1 The electrostatic force on a small sphere of charge 0.4 mC due to another small sphere of charge - 0.8 mC in air is 0.2 N. (a) What is the distance between the two spheres ? (b) What is the force on the second sphere due to the first ? 2. Given electric potential   x2  y2  z2. What is the modulus of electric field at 1, 1, 1 . 3 Two point charges qA = 3 mC and qB = -3 mC are located 20 cm apart in vacuum. (a) what is the electric field at the midpoint O of the line AB joining the two charges? (b) if a negative test charge of magnitude 1.5 x 10-9 C is placed at this point, what is the force experienced by the test charge ? 4 A system has two charges qA = 2.5 x 10 C and q = –2.5 x 10 C located at points A: (0, 0, -15) and -7 -7 V: (0, 0 +15), respectively. What are the total charge and electric dipole moment of the system ? 5 Figure shows tracks of three charged particles in a uniform electrostatic field. Give the signs of the three charges. Which particle has the highest charge to mass ratio ? + + + + + + + + + 1st 2nd 3rd - - - - - - - - - 6 Consider a uniform electric field E = 3 x 103 ˆi N/C. (a) What is the flux of this field through a square of 10 cm on a side whose plane is parallel to the yz plane ? (b) What is the flux through the same square if the normal to its plane makes a 600 angle with the x-axis? 7 A point charge +10 mC is a distance 5 cm directly above the centre of a square of side 10 cm as shown in figure. What is the magnitude of the electric flux through the square ? (Hint : Think of the square as one face of a cube with edge 10 cm.) 8 Two charges 2 mC and -2 mC are placed at points A and B 6 cm apart. (a) identify an equipotential surface of the system (b) what is the direction of the electric field at every point on this surface ? 9 A spherical conductor of radius 12 cm has a charge of 1.6 x 10-7 C distributed uniformly on its surface. What is the electric field (a) inside the sphere (b) just outside the sphere (c) at a point 18 cm from the center of the sphere ? 10 Three capacitors each of capacitance 9 pF are connected in series. (a) what is the total capacitance of the combination ? (b) what is the potential difference across each capacitor if the combination is connected to a 120V supply ? 11 A cube of side b has a charge q at each of its vertices. Determine the potential and electric field due to this charge array at the centre of the cube. 12. An electric dipole with dipole moment 4 x 10-9 Cm is aligned at 300 with the direction of a uniform electric field of magnitude 5 x 104 NC-1. Calculate the magnitude of the torque acting on the dipole. 13. (a) Two insulated charged copper sphere A and B have their centres separated by a distance of 50 cm. What is the mutual force of electrostatic repulsion if the charge on each is 6.5 x 10-7 C ? The radii of A and B are negligible compared to the distance of separation. (b) What is the force of repulsion if each sphere is charged double the above amount, and the distance between them is halved ? 14. Three capacitors of capacitances 2 pF, 3 pF and 4 pF are connected in parallel. (a) What is the total capacitance of the combination? (b) Determine the charge on each capacitor if the combination is connected to a 100 V supply. 15. A charge of 8 mC is located at the origin. Calculate the work done in taking a small charge of – 2 x 10-9C from a point P (0, 0, 3 cm) to a point Q (0.4 cm, 0) via a point R (0, 6 cm, 9 cm).

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