Four identical point charges are fixed at the same distance from point P. "lbe charges are either +Q or -Q.

Each action described is made to the situation shown in the diagram (i.e.. "Change sign of charge 0" means that charges A, C. and D will be positive and charge B will be negative). For each modification:

? Indicate whether the magnitude of the electric field at the origin (i) increases, (ii) decreases, or (iii) remains the same.

? Indicate whether the electric potential at the origin (i) increases, (ii) decreases, or (iii) remains the same. (Use the convention that the electric potential is zero far from the charges.)

? Indicate the direction of the electric field at the origin after the modification. Explain your reasoning.

AO +2 0 OB OD -Q Modification Change the sign of charge A. Change the sign of charge B. Change the sign of charge C. (d) Change the sign of charge D. (e) Change the signs of charges B and D. (f) Exchange charges A and B. Exchange charges A and D. (a) (b) Electric field Electric potential JI |11 iji Electric field direction B D B none none