Supplemental Instruction
Iowa State University
Useful Equations
Leader: Alek Jerauld
Course: PHYS 222
Instructor: Dr. Paula HerreraSiklódy
Date: 1/17/12
 charges
The force exerted on two charged point particles due to their


𝐸 𝑛𝑒𝑡
=
2𝑘 𝑒 𝑟𝐿 line of charge
Constants
𝑄
The electrical field created by a charged point particle
The electrical field at some point r distance above an infinite
Related Problems
1) Two uncharged metal spheres, L and M, are in contact. A negatively charged plastic rod is brought close to L, but not touching it, as shown below. The two spheres are then slightly separated and, after this separation, the rod is removed. As a result of these steps:
A) both spheres are neutral
B) both spheres are positively charged
C) both spheres are negatively charged
D) L is negatively and M is positively charged
E) L is positively and M is negatively charged
2) Find the magnitude and direction of the electrical field at the origin (0,0,0) in terms of q. (Drawing is NOT to scale)
120 mm y
-q
16 cm
-q x
4 cm z
3 cm
+q

3) The diagram below shows the electric field lines in a region of space containing two small charged spheres, Y and Z. We can deduce that:
A) Y is positive and Z is negative
B) the magnitude of the electric field is the same everywhere
C) the electric field is strongest midway between Y and Z
D) a small negative charge placed at point X would experience a force to the left
E) Y and Z must have the same sign
4) A particle with a mass of 10 -4 kg and a charge of +2 µC is moving at a constant horizontal velocity of 3 m/s into an area with an electrical field of 50 N/C. Which point most accurately describes the final resting position of the charged particle?
0.4 cm 0.2 cm
(a) (b)
0.2 cm
E
0.2 cm
(c) (d)
5) Three point charges are arranged on a line. Charge q
3
= +5 nC and is at the origin.
Charge q
2
= -3 nC and is at x= +4 cm. Charge q
1
is at x= +2 cm. What is q
1
(magnitude and sign) if the net force on q
3 is zero?
CHALLENGE!!
6) Positive charge Q is uniformly distributed around a semicircle of radius A.