Question

5. A charge Q is at the origin. Charge q1= +q and charge q= +2q. charge q1 is located at distance r 

away from Q; while q2 is located at distance 2r away from charge Q. Which of the charges is at 

the higher potential (refer to the figure below):

a. Q1

b. Q2

c. Both are at the same potential

6. Refer to question 5. Which charge has the higher electric potential energy?

a. Q1

b. Q2

Both have the same potential energy

7. A 10 mC particle is moved from infinity to a point where the electric potential energy is 5J. What 

is the electric potential at its new location?

a. 2mV

b. 2V

c. 50mV

d. 500V

point A?

Answer 1

5. The higher potential is for charge q1 because it is in the field created by Q, and the potential of this field depends on the value of Q and the distance:

$$V_{\text{at q}_1}=\frac{kQ}{r}.$$

6. Both have the same potential energy:

$$W=\frac{kQq_i}{r_i}=\frac{kQq}{r}=\frac{kQ·2q}{2r}.$$

7. The potential is

$$V=\frac Wq=\frac{5}{0.01}=500\text{ V}.$$