1. AP Physics 2
Ch 15 Review

2. Terms to Remember Electrostatics – study of charges at rest
Electroscope – device that detects the presence of charge by diverging leaves
If charge is present the leaves diverge
Greater charge, greater separation
Negative rod repels electrons to leaves so diverge
Positive rod attracts electrons to rod leaving positive charge on leaves and they diverge

3. Terms to Remember
Conductor – material that allows charge to flow easily
- large number of free electrons
Free electron – outer electrons attached so weakly it can drift throughout the material belonging to no atom in particular
Examples of conductors – metals, human body, earth
If conductor is near or in contact with a charged body all free electrons move in the same direction

4. Terms to Remember
Insulator – material that doesn’t allow charge to flow freely
Examples of insulators – rubber, glass, dry air

5. Ways to Charge an Object
Charging by friction – pull electrons away from one object and transfer to another by rubbing the objects together
Charging by contact – process of giving an object charge by placing it in contact with a charged object

6. Ways to Charge an Object
Charging by induction – process of giving an object a charge due to the presence of a charged object

7. Charge Basic unit of charge = charge of electron
It takes 6.24 x 1018 electrons to make 1 Coulomb
e- = -1.6 x C
p+ = +1.6 x C

8. Charge Mass of e- = 9.11 x 10-31 kg Mass of p+ = 1.673 x 10-27 kg
Mass of n = x kg

9. Coulomb’s Law
Force between any 2 point charges is proportional to the magnitudes of the charges and inversely proportional to the square of the distance between them

10. Coulomb’s Law F = k q1 q2 r2 k = 8.99 x 109 Nm2/C2
q1 and q2 = magnitude of charges
r = distance between charges

11. Sample Problem
Donna and John have masses of 50 kg and 80 kg respectively.
How many protons are there in each person? (Protons make up roughly 55% of the mass of the human body.)
Suppose John and Donna stand 5 m apart. Calculate the force exerted on John’s protons by Donna’s protons.

12. Sample Problem
Hanging from threads are two charged balls made of pith. The balls each have a mass of 0.1 g and a charge of the same magnitude q and are attracted to each other. (a) What is the magnitude of the electric force? (b) What is the magnitude of q? (c) How many electrons have been transferred to or from each ball?

13. Sample Problem
An electron is near a positive ion of charge +9e and a negative ion of charge -8e. (a) Find the magnitude and direction of the resultant force on the electron. (b) Find the magnitude and direction of the electron’s instantaneous acceleration.

14. Sample Problem
Given two point charges q1 and q2 = 4q1, find the position of a third charge q3 relative to the other two charges, such that the resultant force on q3 is zero.