1. Chapter 16-3 – The Electric Field
St. Augustine Preparatory School
April 26, 2016

2. The Electric Field
All charged objects have an electric field set up around themselves.

6. Different electric fields for difference
situations

7. Electric Field
To obtain the electric field of an object of interest, we use something called a test charge.
A test charge is a small, positively charged object.
The charge is a single positive charge, 1.60x10-19C

8. The Test Charge The test charge must b kept small (one proton), or
else it may have an effect
on the object that we are
attempting to analyze.

9. Electric Field Strength
Electric field strength depends on two things:
The amount of charge present
The distance between the two objects
Formula (derivation and explanation on next slides):

10. Electric Field Strength Derivation
We know from before:
And if we can substitute Felec.
Then:

11. Electric Field Strength Formula
E = Electric Field Strength -> N/C
kc = Coulomb’s Constant (8.99x109Nm2/C2)
r2 = distance between the two charges -> m2
q = charge of the object of interest -> C

12. Practice Problem
The nucleus of an atom of silver contains 47 protons. What would the field strength of this nucleus be at a distance of 1.56x10-7m? (answer: 1.5x105N/C)

13. Practice Problems
1. A dime and a nickel are electrically charged. The electric field strength around the dime is 4002 N/C. The nickel has a charge of uC. They are 20.0 cm apart.
How much force is exerted on the nickel by the dime’s electric field?
How big is the charge on the dime?
2. A cloud has –5.00 C of charge and is m above the earth. The ground gains C because of induction.
How many electrons make up the C charge?
What is the electric field strength of the cloud if a test charge is placed on the ground?

14. Solutions
1. a N b. 1.8 x 10-8 C 2. a. 3.13x1019 electrons b. 1.12x106 N/C