Find the equivalent resistance of the circuit shown in figure between the points a and b.Each resistor has a resistances `r`.

Explanation

(a) `R_eff = (r xx r /2r) = r/2 Omega `
` (b) At O current coming to the junction is
current going from BO
= current going along OE
Current on CO = current on OD.
Thus , it can be assumed that current
coming in OC goes in OB. Thus,
`[[r+(2r^2/3r)+r] = 2r + (2r/3) = 8/3] `
` R_eff = ((8r/6) xx 2r/(8r/6) +2r)`
` =8r^2 xx 2/20r = 8r/10 = 4r/5`.