Transcript 2-27 Potential Energy, Potential, and Work

Today 2/27
Read Ch 19.1 and 19.4 Skip 2-3 for now
Electric Potential Energy, PEE
Electric Potential, V
Electric Potential Difference, V
(watch out foe +/- signs!!!)
HW:
“Electric Potential Energy”
Due Monday 3/3
Problem:
Two identical point charges of 0.01g are placed 1m
apart. The right-hand charge is released. Find its
velocity when it is 10cm farther away.
v=0
v=?
Two opposite point charges of 0.01g are placed 1m
apart. The right-hand charge is released. Find its
velocity when it is 10cm closer.
v=?
v=0
Problem:
Two identical point charges of mass of 0.01g are placed
1m apart. The right-hand charge is released. Find its
velocity when it is 10cm farther away.
E Field and Force are not the same
everywhere so Fnet = ma requiresv calculus.
=0 v=?
Also need a system to handle direction.
Two opposite point charges of 0.01g are placed 1m
apart. The right-hand charge is released. Find its
velocity when it is 10cm closer.
v=?
v=0
Energy buckets are the way!
Problem:
Two identical point charges og mass .01g are placed 1m
apart. The right-hand charge is released. Find its
velocity when it is 10cm farther away.
A
Initial PE at A?
Initial KE at A?
B
v=0 v=?
0
PEE KE
PEE KE
PEA,B = - KEA,B
Final PE at B? (More or less than before?) Subscripts tell us
from A to B
Final KE at B? Equals the PE lost!
“Potential Energy Difference”
and “Potential Difference”
Potential Energy Difference PEA,B is the
change in PE the particular charge feels when it
is moved from one location to another.
Potential Difference VA,B is the change in PE a
positive 1C charge would feel if it were moved
from one location to another.
VA,B = +108 Volts,
and q = +1C
PEA,B = +100J
VA,B = -108 Volts,
and q = +1C
PEA,B = -100J
Which way does the E Field point?
PEA,B =
+100J, and q =
+1C What is
VA,B?
Remember:
From A to B!!!
VA,B = 108 Volts
Higher
Potential
E field
A
Higher
Potential
B
PEA,B =
E field
+100J, and q =
VA,B = -108 Volts
-1C What is
VA,B
? “downhill” with respect to potential difference
E Fields
point
What about Work, WA,B?
PEA,B =
+100J, and q =
+1C What is
VA,B?
Remember:
From A to B!!!
VA,B = 108 Volts
+Work
Higher
Potential
E field
A
Higher
Potential
B
+Work
PEA,B =
E field
+100J, and q =
VA,B = -108 Volts
-1C What is
VA,B
? “downhill” with respect to potential difference
E Fields
point