Download 03.EFieldNotesAndProblems

ELECTRIC FIELDS NOTES and PRACTICE PROBLEMS
PART 1: Notes on Electric Fields
 Two charged objects _______ need to touch each other to experience _______ or
_______________
 _______________ has a small space around it where other objects will “feel” its charge. This is called
____________________.
 We can test for what kind of charge the electric field is by using a very small _______________ (like a
hockey puck ) and see whether it attracts or repels.
 A test charge will experience an electric force, Fe when placed in an electric field
o A _______________ charge repels the positive test charge
o A _______________ charge attracts the positive test charge
 What 2 things does the strength of the electric field depend upon? ________________________________
 We can visualize the electric field that results for any combination of charges by drawing electric field
lines.
 Rules for drawing electric field lines:
1. Arrows represent the direction of the electric field
2. Field lines always point ___________________ to the surface of the charge
3. The ______________ of the electric field is represented by how close together the lines are
4. Arrows point _____________ negative charges (representing the attractive force due to a positive
test charge)
5. Arrows point __________________ positive charges (representing the repulsive force due to a
positive test charge.
6. For two charges with overlapping electric fields, the lines represent the ______ force that a positive
test charge would feel at various locations near the charges
7. For two charges with overlapping electric fields, the lines represent the net force that a positive
test charge would feel at various locations near the charges.
8. ________ the density of lines surrounding any given object
_______ the quantity of charge on the source charge, and
_____________ the strength of the field at that location.
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PART 2: Measuring the Strength of Electric Fields:
An electric field is set up by a source charge (Q). When placed in an electric field, a test charge (q) will experience an
electric force Fe. The electric field intensity is how much force is felt per charge q.
where
units: N/C
E = Electric Field Intensity
Fe = Force on the test charge q
q = a positive test charge
REMEMBER COULOMB’S LAW: The electric force also depends on _____________ the two charges are:
Q = the charge that sets up the electric field
d = the distance from the source charge.
Practice Problems
1) A positive test charge of 3 x 10-6 C is placed in an electric field where it experiences a force of 0.85 N.
What is the electric field intensity?
2) A fly accumulates 4 x 10-10 C of positive charge as it flies through the air. What is the magnitude and
direction (towards the fly or away from it?) of the electric field at a location 2.0 cm away from the fly?
3) Practice drawing electric field lines on the attached worksheet.