Download Practice Problems: Coulomb`s Law and Electric Field Strength

Practice Problems: Coulomb’s Law and Electric Field Strength
K  q  q
F
d2
d
K  q  q
F
F d2
q' 
K q
K  9.0 x10 9
qe  1.6 x10 19 C
E
1C  6.25 x1018 e 
F = ____________; unit is ____________
d = ____________; unit is ____________
q = charge; unit is Coulomb (C)
K = 9.0 x 109 Nm2/C2
F
q
E = electric field strength; unit is Newtons per Coulomb (N/C)
1. A balloon is given a charge of –15 C by rubbing it on some hair.
a. If the hair and balloon are 0.02 m apart, how much force is between them?
b. Will they attract or repel each other?
c. How much strength does the electric field have?
2. A pair of dimes is electrically charged. The electric field strength around one dime is
4000N/C. That dime has a charge of +20 C and the other one’s charge is unknown. They are
20 cm apart.
a. How much force is between the dimes?
b. How big is the charge on the unknown dime?
3. A cloud might have –5 C of charge and be 200 m above the earth. The ground gains +3 C
because of induction.
a. How much force will be unleashed by the bolt of lightening that follows?
b. How strong is the electric field around the cloud?
4. If the clouds charge was doubled, what would happen to the force of the bolt? (Do a
calculation to check your prediction.)
5. If the clouds were half as high up off the ground, what would happen to the force of the bolt?
(Do a calculation to check your prediction.)