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Class 12 14-5-2018 Time : 1 hr. M. Marks : 20 Class Test in PHYSICS 1. Flux is scalar or vector? What do you mean by negative flux? (1) 2. Define Dipole moment of a dipole. Write its SI unit. (1) 3. Write two characteristics of charging a conductor by induction method. (1) 4. Two identical charges are separated by some distance. What are the electrostatic characteristics of the mid point of two charges? (1) 5. Two charges 4 C and 16 C are separated by 9 cm. Locate a point on line joining the charges where the resultant electric field is zero. (2) 6. Explain with the help of neat diagram the principle of electrostatic shielding of a conductor. Give an example of it. (2) 7. Three point charges Q, 4Q and 2Q are placed at the vertices of an equilateral triangle ABC of sides a as shown in the figure. (i) Obtain the expression for the magnitude of the electrostatic force experienced by Q due to other charges (ii) Find out the amount of work done to separate the charges to infinite distance. (3) A 4Q B Q 2Q a C 8. An electric dipole is placed in a uniform electric field E with its dipole moment making an angle of with electric field. Show that net force acting on it is zero. Write the expression of torque. Derive an expression for work done in rotating the dipole in the electric field. What is the characteristic of this work done? (3) 9. Charge q is placed at a perpendicular distance r1 from an infinitely long linear charge distribution of uniform charge density . Calculate the work done in bringing the charge to a perpendicular distance r2 (r2 > r1). (3) 10. State Gauss s law of electrostatics. Use Gauss s law to derive an expression for the electric field intensity a point outside a uniformly charged conducting shell of radius R. Hence establish an expression for the electric field at a point very close to the shell. What is the nature of this field? (3) -x-x-x-x-x-x-x-
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