How much electric field is necessary to hold a polystyrene ball of mass 100 gram

Question

How much electric field is necessary to hold a polystyrene ball of mass 100 gram in air. Assume the charge of the ball is 2 C. What IS the potential at point P as shown in the figure at your right? 0 V k V 2K V 3k V 4k V What is the direction of electric field at point P in above figure if +2C at right is replaced with negative 2C? North, Youth, West, East A parallel plate capacitor consists of two strips of aluminum foil, each with an area of 1.0 m^2, separated by a distance of 0.10 mm. The space between the foils is empty. What is the capacitance? 10epsilon_0 F 100epsilon_0 F 1000epsilon_0 F 10000epsilon_0 F none If charge at C point is positive and charges at point A and B is negative, then resultant force on B will come from the force pair F1 & F2, F10 & F9, F3 & F4, F4 & F2, F1 & F4 In the given magnetic field B, a positive charge is moving in the direction indicated. What is direction of force on the moving charge? Youth, North, East, West, None A piece of aluminum wire with circular cross section has resistivity p. If the diameter of the cross section is 2 mm and length is 40 cm, what is the resistance of that sample?

Explanation / Answer

15)    Here, qE = mg

=> E = 0.1 * 9.8/2 =   0.49 N/C

16)   Potential at P =    k * 2/1 + k * 2/2

                               = 3k V

17) Direction of electric field = West

18)    capacitance   =   eo * 1/(0.10 * 10-3)

                               =   10000e0 F

19)     F10 and F9 .

20)    North .

21)    resistance of sample = (2.65 * 10-8) * 0.4/(3.14 * 10-3 * 10-3)

                                          = 3.375 * 10-3 ohm  

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