University Physics-PHYS 221, Fall 2000, UT Martin

                        Quiz 3 (Electric Potential)


            Constants: e= 1.60x10-19C, k = 9.0x109 N.m2/C2. me=9.11x10-31 kg.


___1)When two point-like charges are moved toward each other, their electric potential energy decreased.  Therefore

a)      they are both positive,

b)      they are both negative

c)      one is positive, the other is negative.


___2) The electric potential of a point-like charge at a distance r from the charge is

2 V.  The electric potential at a point 2r distance from the charge is,


a) 2 V        b) 4 V              c) 1V               d) 0V               e) 8V


___3) The electric potential as a function

of distance through x axis is given below.

Rank the regions according to the magnitude

 of the x component of the electric field, from

 greatest to least.


a) 1,2,3,4               b)2,1,4,3


c) 2,3,4,1               d)3,2,1,4



___4) Electric field lines run from _________potential to ________potential.


a) high, low b) low, high



___5) The figure shows three pairs of parallel plates

with the same separation, but with different potentials.

Rank the pairs according to the magnitude of the

electric field, greatest first.

a) A,B,C    b)B,C,A           c)C,A,B    

d)another combination that is not given above                     



6)When an electron moves from A to B along an electric field line, the electric field does 3.2x10-16 J of work.  What is the electric potential difference VA-VB?








7) A parallel plate capacitor is connected across the terminals of a 10 V battery.  The plate separation is 1 cm. 


a)      What is the magnitude of the electric field?        






b)      Sketch several of the electric field lines including direction.




c)      Which plate is at a higher potential, lower or upper?





d)      A positive charge, +2C, is moved from top plate to the bottom plate.  How much did its electric potential energy change?






e)      How much work is done by the field during the charge’s movement from top to the bottom plate?







8) Two equal and opposite point-like charges are fixed in the positions shown below.   A is a field point at 4m from both charges.




a)      What is the electric potential energy of the system of two charges?







b)      What is the total electric potential at point A?