# electric field and electric force by point charge

1) How many coulombs of positive charge are there in kg of carbon? Twelve grams of carbon contain Avogadro's number of atoms, with each atom having six protons and six electrons.

2) Three charges, each of magnitude nC, are at separate corners of a square edge of length 5 cm. The two charges at opposite corners are positive, and the other charge is negative. Find the force exerted by these charges on a fourth charge q = +3 nC at the remaining corner.

3) A charge of 4.0 C is at the origin. What is the magnitude and direction of the electric field on the x axis at (a) x = 6 m, and (b) x = -10 m? (c) Sketch the function , versus x for both positive and negative values of x. (Remember that is negative when E points in the negative x direction.

4) A point charge of +5.0 C is located at x = -3.0 cm, and a second point charge of -8.0 C is located at x = +4.0 cm. Where should a third charge of +6.0 C be placed so that the electric field at x = 0 is zero?

5) An electron with kinetic energy of 2 x J is moving to the right along the axis of a cathode-ray tube. There is an electric field =(2 x N/C) in the region between the deflection plates. Everywhere else, = 0. (a) how far is the electron from the axis of the tube when it reaches the of the plates? (b) at what angle is the electron moving with respect to the axis? (c) at what distance from the axis will the electron strike the fluorescent screen?

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