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Physics: Ch20-21 Electrostatics
Notes1: Electric Fields
FORCE FIELDS
What is a force field?
An invisible, massless goo that exists in a region that exerts a
______________ on certain objects.
These fields are a property of space.
These things experience a force without being _________________.
You can think of the forces as interactions between the field and the thing.
Only certain things in a force field experience a ______________.
For example, in a gravitational field, things that experience a force have
_________.
Force fields must have some ___________.
A gravitational field is caused by things with __________.
You can not see, hear, taste, smell or touch a force field but, can you feel it?
ELECTRIC FIELDS
An electric field is caused by ______________________.
Electric fields exert a force on anything that has ___________________.
Electric fields have a size (or _______________) and a ____________.
The bigger the size of the electric field, the bigger the ______________ on
the charged object in that field.
The direction of the field is related to the direction of the ____________ on
the charged object.
ELECTRIC FIELD DIRECTION
An electric field has a direction.
The force on a _____________ charge is in the __________ direction as the
electric field.
The force on a _____________ charge is in the __________ direction as the
electric field.
ELECTRIC FIELD DIRECTION EXAMPLES
In the two examples below, draw an arrow at point A in the direction of the
electric field. Label the arrow “E-field.”
Hint: Imagine a positive charge at point A and determine the direction of the
force on it.
A) Positive Charge
+
B)
A
Negative Charge
A
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Now, go back and add 2 more arrows: One pointing the in direction of the
force on a positive charge (label that “Force on pos.”) and one arrow pointing
in the direction of force on a negative charge (label that “Force on neg.”)
Do worksheet #1
ELECTRIC FIELD STRENGTH
To measure electric field strength, we put a positive ________________ in
the electric field and measure the ______________ on that test charge.
Then:
E = F on q'/q'
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Where:
E = Electric field
q' = _____________ (Coulombs)
F on q' = _________ on test charge
Units of electric field (E) are N/C (__________ per ___________)
The electric field does not change with the size of the ________________.
Recall Coulomb's Law:
Let's say our test charge is qA . If qA doubles, then the force ___________.
The ratio of F to charge will be ____________. So, electric field
__________________.
The electric field ___________ change with the amount of charge you put in
the field but the __________ on that charge does.
ELECTRIC FIELD LINES
Recall: Electric fields have 2 properties (like any vector): a ___________ and
____________.
Electric field lines are used to show the _____________ and ____________
across a region.
Arrows on the lines point in the _______________ of the electric field.
The closer together the lines are, the ______________ the electric field is.
Which of the following represents a larger electric field?
Rules for drawing electric field lines:
1) Electric field lines ________ at positive charges
2) Electric field lines ________ at negative charges
3) The arrow points way from ___________ charges and towards
___________ charges.
4) Electric field lines are __________________ when the field is stronger
and ______________________ when the field is weaker.
5) Electric field lines do not ______________ each other.
Examples:
1) Draw the electric field lines for one small object with a positive charge:
+
ADDING ELECTRIC FIELDS AND LINES
Examples:
2) Draw the electric field lines for two small object: one with a positive
charge and the other with a negative charge:
+
-
3) Draw the electric field lines for two plates: one with a positive charge
and the other with a negative charge:
+
+
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+
+
+
+
+
+
+
+
+
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+
-
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