Question

Find equivalent resistance btw M nd N.

Answer 1

Final Answer :2R

STEPS:
1) We will draw the Resistance diagram in easy way which is sufficient to calculate R(eq) .
So, we will mark every junction points and make in simple way as shown in diagram.

2) In Next, diagram :
BOXED RESISTORS make a Wheatstone Bridge.
So,
Current will not pass through DC wire by concept of Wheatstone Bridge.

3) Hence, we will further redraw our final Diagram in pic 2 .
Here,
Upper Branch resistors are in series.
So, R(eq) 1 = R+ R = 2R
Similarly,
In Lower Branch,
R(eq)2 = R+ R = 2R

4) Then, Upper Branch and Lower Branch are in parallel.
So,
$\frac{1}{r(eq3)} = \frac{1}{r(eq2)} + \frac{1}{r(eq1)} \\ = > \frac{1}{r(eq3)} = \frac{1}{2r} + \frac{1}{2r} \\ = > r(eq3) = r$

5) Now,
r(eq3) and R are in series,
Therefore,
R(eq) = R + R = 2R

Hence, equivalent Resistance between M and N is 2R.