Brock University
Physics 1P22/1P92
Winter 2015
Dr. D’Agostino
Tutorial 2 (Chapter 19: Electric Potential Energy and Electric Potential)
Questions
Purpose: To understand electric potential and electric potential energy.
1. A negatively charged particle B is released from rest near a negatively charged particle A.
Particle A is fixed in place.
(a) Describe the subsequent motion of Particle B. Include a sketch.
(b) Describe how the potential of Particle B changes as it moves.
(c) Describe how the potential energy of Particle B changes as it moves.
(d) Describe how the speed of Particle B changes as it moves.
(e) Describe how the acceleration of Particle B changes as it moves.
(f) Does the electric force exerted by Particle A on Particle B do positive work, negative
work, or zero work on Particle B as Particle B moves? Explain.
2. Particle C is positively charged and fixed in place. Particle D is also positively charged.
Particle D is moved in a circular path by some external forces, and the centre of the circle is
at the location of Particle C. Does the electric force exerted by Particle C on Particle D do
positive work, negative work, or zero work on Particle D as Particle D moves?
3. You have a capacitor with capacitance C. You place a dielectric with dielectric constant 3.1
between the electrodes of the capacitor. Does the capacitance of the capacitor change? If so,
why? If so, exactly what is the change?
4. You have a capacitor with capacitance C connected to a battery with voltage V . You place
a dielectric with dielectric constant 1.7 between the electrodes of the capacitor. Does the
charge on each plate of the capacitor change? If so, why? If so, exactly what is the change?
5. You have a capacitor with capacitance C connected to a battery with voltage V . Once
the capacitor is fully charged, you disconnect the battery. Then you place a dielectric with
dielectric constant 1.7 between the electrodes of the capacitor.
(a) Does the charge on each plate of the capacitor change? If so, why? If so, exactly what
is the change?
(b) Does anything change when the dielectric is inserted? If so, what changes, and why?
6. Rank the positions according to their potentials, in order from highest to lowest. The electric
field is uniform.
1
−
+
+
A
−
B
+
C
+
+
−
D
−
E
+
F
+
−
−
−
−
+
7. Rank the positions according to their potentials, in order from highest to lowest. The electric
field is caused by a negatively charged particle indicated by the “”.
A
B
C
D
F
E
8. Determine the potential difference between the plates of a 3.3-F parallel-plate capacitor that
stores sufficient energy to operate a 75-W light bulb for one minute.
9. Consider a square of side length 1.0 cm that has a positively charged particle with charge
+7.9 nC at each corner of the square.
(a) Determine the electric potential at the centre of the square.
(b) Determine the electric field at the centre of the square.
2