1) For a positively charged sphere, the electric field lines point outward. For a negatively charged sphere, the electric field lines point inward. Why is it always like that?
2) A charge (3.6x10^-6 C) is 30cm to the left of another charge (-2.7x10^-6 C). Point A is 20cm to the right of the charge with -2.7x10^-6.
a) Find the magnitude and direction of the net electric field at point A.
b) What electric force is exerted on a charge 4.5x10^-6 C placed at point A?
c) What electric force is exerted on a charge -4.5x10^-6 C placed at point A?
[For part a, I got an answer of 4.8x10^5 N/C [left]
For part b, would the electric force have the same direction as the electric field at point A? (i.e. left?) I assumed so, and got an answer of -2.2N
The main problem is part c. I don't know how to calculate this. We know that
E =
Fe/q, where E represents the electric field, Fe is the electric force, and q is the magnitude of the charge at point A. Note that in the equation, q is substitute as a magnitude. So would the negative charge affect anything, will the answer be the same as part b?]
3) A negative charge of 2.4x10^-6 C experiences an electric force of magnitude 3.2 N, acting to the left.
a) Calculate the magnitude and direction of the electric field at that point.[The answer is 1.3x10^6N/C[right]. Why is the direction to the right? The electric force has a direction to the left, and since electric force and electric field always have the same direciton, shouldn't the direction of the electric field be to the left also?]
b) Calculate the value of the field at that point if a charge of 4.8x10^-6 C replaces the charge of 2.4x10^-6 C.
4) Consider the setup of two large, equally charge, parallel, flat conducting plates close together, the top plate positive and the bottom plate negative.
-The electric field is constant everywhere in the space between the parallel plates. [WHY?]
-The magnitude of the electric field at any point between the plates depends and is directly proportional ONLY on the magnitude of the charge on each plate. [Why is it so? I thought that E=Fe/q is the formula for electric field, shouldn't E be inversely proportional to q? (E=electric field, q=charge]
-The plate separation has no effect on the electric field. [WHY?]
Could anyone explain? I will really appreciate for your help!
