Transcript Friday`s Slides

W5D3 POTENTIAL & MORE
POTENTIAL
Let’s Discuss the last Worksheet
Electric Potential
I. Work and Potential Difference
Work and Potential Difference
An object travels from point A to point B while two constant
forces of equal magnitude, and , are exerted on it. Think about
the work done by each force and the net work.
Is the work done on the object by F1 positive, negative, or
zero?
A
B
C
D
Positive
Negative
Zero
More information is needed
A

F2

F1
B
Work and Potential Difference
An object travels from point A to point B while two constant
forces of equal magnitude, and , are exerted on it. Think about
the work done by each force and the net work.
Is the work done on the object by F2 positive, negative, or
zero?
A
B
C
D
Positive
Negative
Zero
More information is needed
A

F2

F1
B
Work and Potential Difference
An object travels from point A to point B while two constant
forces of equal magnitude, and , are exerted on it. Think about
the work done by each force and the net work.
Is the work done on the object by the net force positive,
negative, or zero?
A
B
C
D
Positive
Negative
Zero
More information is needed
A

F2

F1
B
Work and Potential Difference
An object travels from point A to point B while two constant
forces of equal magnitude, and , are exerted on it. Think about
the work done by each force and the net work.
Is the magnitude of the velocity of the object at point B
greater than, less than, or equal to the velocity of the object at
point A? Explain how you can tell.
A
B
C
D
Positive
Negative
Zero
More information is needed
A

F2

F1
B
Work and Potential Difference
An object travels from point A to point B while two constant
forces of equal magnitude, and , are exerted on it. Think about
the work done by each force and the net work.
Which, if any, of your responses to questions 1, 2, 3, or 4
would change if the magnitude of F1 was twice as great as
the magnitude of F2 ?
A

F2

F1
B
Quick Summary




If the net force on an object is zero but it is moving from
Point A to Point B, it is in equilibrium and is moving at
constant velocity.
If the net force on this object is NOT zero, then it is
accelerating and gaining energy (Kinetic).
In the absence of any other forces, the net work done by
these forces is equal to the change in kinetic energy + the
change in potential energy.
REMEBER: PE=qV

UNITS OF V is VOLTS. (Big surprise).
Klick
Which arrow best represents
the electric field at the "x"?
Consider the following:
+Q
Area = A
s=Q/A
D
-Q
UNIFORM ELECTRIC FIELD
E
s
E
0
A Capacitor is a device like the above that STORES CHARGE.
There is a potential difference between these two plates. (V)
The capacitance C is equal to the charge/potential difference.
C=Q/V
Q=CV
Consider the following:
+Q
D
so       
-Q
sD
V  ED 
0
Area = A
s=Q/A
UNIFORM ELECTRIC FIELD
E
s
E
0
Q  CV  s A
C
sA
V
Work needed to move unit charge from A to
B also is (magnitude, anyway) FxD=ED
(unit charge)
sA
V
s 0

V
D
A
C  0
D
C
So .. What does it all mean??
C
0 A
The capacitance of a parallel plate
capacitor depends only on geometrical
factors.
D
NOT on charge or potential difference!
Moving charges in a capacitor while they are in equilibrium
HUH??
Mr. External
Ms. Field
WORKSHEETS – Electric Potential