# Physics Toolbox: Circuits

Mechanics

Nov 14, 2013 (4 years and 8 months ago)

86 views

Physics Toolbox:
Circuits

These equations
will

be given on the exam

because they are less fundamental than others
:

2
2
( )
( )
dU V
P I R I V
dt R

    

2
2
1 1
( ) ( )
2 2 2
Q
U C V Q V
C
    

L L
R
A A

 

E
J E

 

These equations
will not

be given on the exam because they contain foundational concepts that we
want you to remember after the semester ends:

dq
I
dt

I
J
A

V
I
R

Q
C
V

1
1
series
1 1
parallel
N
eq i
i
N
i
eq i
R R
R R

1
1
parallel
1 1
series
N
eq i
i
N
i
eq i
C C
C C

1
Loop rule: 0
Junction rule:
N
loop
i
i
in out
V V
I I

   

 

K
now how to derive these equations for current, voltage, and charge as a function of time for
discharging
and
charging capacitors.

(You might want to just memorize the
m
, too.)

Discharging:

Charging:

0
( )
t RC
I t I e

0
( )
t RC
I t I e

0
( )
t RC
V t V e

max
( ) 1
t RC
V t V e

 

0
( )
t RC
Q t Q e

max
( ) 1
t RC
Q t Q e

 

Time constant =
RC