Transcript Electric Fields - 2010-ComprehensivePortfolio

BW
• Draw the distribution of
charges of an electroscope
when it is charged by
bringing a glass rod that was
rubbed against silk near its
probe.
BellWork
• If two charges of +1.6x10-19 C are
separated by a distance of 2 meters, what
is the electrostatic force between them? Is
it attractive or repulsive?
+1.6x10-19 C
+1.6x10-19C
2 meters
BW
• What charge does the dome of a van de
Graff generator have?
Electric Fields
• Electric Field – the region around a
charged particle through which a force is
exerted on another object.
Electric field lines
• Imaginary line along which a positive test
In other words, the direction of
charge would move
an electric field is direction of
the force on a stationary
positive charge located any
point on the field line (tangent
to the line for a curved field
line)
Positively
Charged
Sphere
+Q
Negatively charged sphere
-Q
Between Opposite Charges
+
-
electric field lines go from positive to negative charges and
never intersect
Between Positive Charges
+
+
Between Negative Charges
-
-
Between Opposite Charged Plates
+ + + + + + + + + + + + + +
+
Uniform Field
net force same
+
Fnet
+
Fnet
Fnet
- - - - - - - - - - - - - -
The Field
+ + + + + + + + + + + + + +
- - - - - - - - - - - - - -
Identify the following particles, given the electric fields:
Draw the electric field lines between these particles:
1.
+
+
3.
+
2.
+
-
BW
• Draw the electric field lines between these
charged particles:
+
+
Electric Field Strength
• The force on a test charge
per unit charge
• E = electric field strength (N/C)
• Fe = electrostatic force (N)
• q = electric charge (C)
Fe
E
q
•The electric field strength is directly proportional to the electrostatic force.
•If E increases, then Fe increases. If E decreases, then Fe decreases.
How does this relate to distance?
Example
• What is the magnitude of the electric
field strength at a point in a field where
an electron experiences a 1.0 N force?
If a proton is found in an electric field with a
strength of 10 N/C, what is the electrostatic force
that the proton experiences?
What are the magnitude and direction of the electric field 1.5 m away from
a positive charge of 2.1*10-9 C?
From the diagram of A and B above, rA is 0.0005 m and rB is 0.0003 m. What is
the force acting on q at A and B, if the charge of q is 1.2 * 10-11 C and the charge
of Q is 1.5 * 10-11 C?
For situation A and B above, calculate the electric field for the charge Q
passing into charge q’s electric field.
CONDUCTING SPHERE
• On the surface, charge is distributed
uniformly (evenly).
• Electric field lines are normal
(perpendicular) to the surface.
• Electric field strength varies with the
square of the distance, just as a point
charge.
Hollow Sphere
The electric field stength
inside a hollow, charged
conducting sphere is zero