Thévenin and Norton 1

.PS
include(pstricks.m4)

scale=25.4

cct_init

define(`termrad_',`sourcerad_/4')
define(`terminal',`circle rad termrad_')

vsp=20
hsp=25

O: (0,0)

move to O

Vs: source(up_ vsp,V,);llabel(,v_s,);rlabel(,15\;\text{V},)
line right hsp
{ dot(at Here)
  R1: resistor(down_ to (Here.x,O.y));rlabel(,R_1,);llabel(,7\;\Omega,)
  dot(at Here)}
line right hsp
{ dot(at Here)
  R3: resistor(down_ to (Here.x,O.y));rlabel(,R_3,);llabel(,24\;\Omega,)
  dot(at Here)}
{ line up vsp
  Is1: source(right_ hsp,I,,R);llabel(,i_{s1},);rlabel(,1\;\text{A},)
  line down to (Here.x,R1.start.y)
  dot(at Here)}
R4: resistor(right_ hsp);llabel(,R_4,);rlabel(,8\;\Omega,)
{ line right hsp/2
  Ta: terminal}
Is2: source(down_ to (Here.x,O.y),I,,R);rlabel(,i_{s2},);llabel(,2\;\text{A},)
dot(at Here)
{ line right to (Ta.w.x,Here.y)
  Tb: terminal}
line left to R3.end
R2: resistor(left_ to R1.end);llabel(,R_2,);rlabel(,12\;\Omega,)
line to O

"$_a$" at Ta.n above
"$_b$" at Tb.s below

.PE