Nine wires each of resistance are connected to make a prism as shown in figure. Find the equivalent resistance of the arrangement across
a.`AD` b. `AB`

Answer

A, B, C

Explanation

a. Due to symmetry about the shadded plane, current distribution on either side of the plane will be identical and points E and F will be at same potential and no current will flow through it

`:. R_(AD)=(2/3rxx8/3r)/(2/3r+8/3r)=8/15r`
b. Redrawing the given arrangement for resistance across AB. Potentials `V_D=V_E`

`V_C=V_F`
`:.` No current flows through `DE` and `CF`.
`:.R_(AB)=(3/2rxxr)/(3/2r+r)=3/5r`