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Worksheet 6.4 – Potential Energy
1. What is the electric potential at a point 6.7 m away from a +45 μC Charge?
2. What is the electric potential midway between two charges shown below:
6.4 m
+1.3 μC
+6.4 μC
3. A 23 μC charge is placed 4.3 m away from a 345 μC charge. What is the potential energy for these two
charges?
4. Two equal charges contain a total of 3.5 J of potential energy when they are 5.6 m apart. What is the
charge of one of the particles?
5. A 34 μC positive charge is initially placed 2.6 m away from a 78 μC positive charge. The 34 μC charge
is then moved to a position of 1.2 m away from the 78 μC charge as shown.
2.6 m
1.2 m
78 μC
34 μC
a. What is the work done in moving the 34 μC charge?
(Remember: Work = ΔEp)
b. How much force is required to make the 34 μC move as indicated above?
6. An alpha particle (4 x mass of a proton and twice its charge) is travelling at 2.4 x 106 m/s when it is
8.0 m away from a 7.6 x 10-5 C positive charge. What is the alpha particle’s distance of closest
approach (how close can the alpha particle get to the charge)?
7. A proton is initially held at rest 1.3 m away from a 65 μC charge. The proton is then released and
begins to accelerate away from the 65 μC charge.
7.8 m
v=?
1.3 m
v = 0 m/s
65 μC
1. What speed will the proton have at a distance of 7.8 m away from the 65 μC charge?
2. An electron replaces the proton and the 65 μC is replaced with a -65 μC charge. Explain why is
the speed of the electron is much greater than the proton even though they both start with the
same potential energy?
8. The following diagrams show an electric field with two points, 1 and 2, positioned within the field. Point
1 is a positive test charge. For each diagram indicate:
i. If work is done on the charge with it moves from position 1 to position 2
ii. Where is electric potential energy the greatest – position 1 or position 2
iii. Where is electric potential the greatest – position 1 or position 2
A.
C.
B.
D.
Answers:
1.
2.
3.
4.
5.
6.
7.
6.0 x 104 V
2.2 x 104 V
11 J
47 μC
a. 53 J b. 38 N
0.86 m
a. 2.7 x 106 m/s b. the force is the same but the electron is lighter and therefore accelates at a greater
rate
8. a. No; 1; 1 b. Yes; 2; 2 c. No; 1; 1 d. Yes; 2; 2