17.6 CHAPTER 17. ELECTROSTATICS
Chapter 17 — Summary
See the summary presentation ( Presentation: VPltf at http://www.everythingscience.co.za)- Objects can be positively, negatively charged or neutral.
- Charged objects feel aforce with a magnitude.This is known as Coulomb’s law:
F = kQ 1 Q 2
r^2- The electric field due to a point charge is givenby the equation:
E =
kQ
r^2- The force is attractive for unlike charges and repulsive for like charges.
- Electric fields start on positive charges and endon negative charges.
- A charge in an electricfield, just like a mass under gravity, has potential energy which is related
to the work to move it. - A capacitor is a devicethat stores charge in a circuit.
- The electrical potentialenergy between two point charges is given by:
U =
kQ 1 Q 2
r^2- Potential difference is measured in volts and is given by the equation:
V =
W
q- The electric field is constant between equally charged parallel plates. The electric field is given
by:
E =
V
d- The capacitance of a capacitor can be calculated as
C =
Q
V
=
� 0 A
dChapter 17 End of Chapter Exercises
- Two charges of +3nC and−5nC are separated by a distance of 40cm. What is the
electrostatic force between the two charges? - Two insulated metalspheres carrying charges of +6nC and−10nC are separated by
a distance of 20 mm.
(a) What is the electrostatic force between the spheres?
(b) The two spheres aretouched and then separated by a distance of 60mm. What
are the new charges onthe spheres?
(c) What is new electrostatic force between thespheres at this distance?