Electrostatics Practice Questions
True/False
_______1.
An electric field constant in strength and direction is directed to the right. A proton is
placed in the field. The force of the field on the proton is to the left.
_______2.
Electric field lines leave positive charges and enter negative charges.
_______3.
Electric potential (voltage) is defined as electric potential energy per unit of charge.
_______4.
No two electric field lines can cross.
_______5.
Charged particles must follow the electric field lines in their vicinity
_______6.
It is possible to charge an object without touching it with another charged object.
_______7.
The only way a suspended pith ball can be attracted to a charged ebonite rod is if the ball is
negatively charged.
_______8.
The electron’s mass is approximately two thousand times that of the proton.
_______9.
When a positively charged rod touches a neutral electroscope, protons are transferred to the
electroscope.
_______10.
Equipotential lines are perpendicular to the electric field at every point.
_______11.
An insulator/dielectric reduces the capacitance of a capacitor
_______12.
The electric field inside a conductor is zero.
_______13.
No electric field exists inside a hollow insulator.
_______14.
Objects containing more of one type of charge than another are electrically neutral.
_______15.
Atoms are electrically neutral because the number of protons in them equals the number of
neutrons.
Problems
1. Find the electrostatic force between a +25 μC sphere and a -45 μC that are 1.43 m apart.
2. Find the strength of an electric field at a point 3.2 m from a charged sphere with 275 μC?
What is the electric potential at that position?
3. An electric field has a strength of 4500 N/C. What force is exerted on a +125 μC sphere?
4. What is the energy stored in a capacitor of capacitance 1.5 F and charged to a voltage of 120
V. How much charge resides on each plate of the capacitor?
5. How much work is done on an electron which is accelerated between the two charged parallel
plates, A & B that are 2 m apart. (a) What is the potential difference VB - VA? Assume there is a
uniform electric field of 2000 N/C. (b) What is the electron’s final velocity if it started from rest?
(me = 9.1 x 10-31 kg)?
6. A charged oil drop is suspended in an electric field and is motionless. If the mass of the
droplet is 4 x 10-9 kg, and the strength of the electric field is 5000 N/C and pointing upwards,
what is the a) nature of the charge on the droplet; positive or negative? and b) amount of
charge on the droplet? c) how many excess protons or electrons does it have?