Question

Calculate the equivalent resistance for the following :

Answer 1

1. First diagram.

    100 ohms and 25 ohms connected to B, are in parallel.

     So equivalent resistance = R1 = 25*100/125 = 20 Ohms

     R1 is in series with 100 ohms. SO  R2 = 120 Ohms.

    This R2 and 120 ohms connected to B are in parallel.

    Equivalent of these two = 120/2 = 60 ohms.

    This 60 is in series with 100 Ohms.  So  160 Ohms.

    160 Ohms and 40 are in parallel between A and B.

    Net :   40*160/(40+160) = 32 Ohms.    ANSWER

 

2.

    30 Ohms and 40 Ohms are in series.  So  70 Ohms.

     That is in parallel with 20 Ohms and 10 Ohms

     So we get   1/R = 1/20 + 1/10 + 1/70 = 23/140  => R = 140/23 Ohms

    R is in series with 50 Ohms.   So we get  140/23 + 50 = 1290/23 ohms

   This is parallel with 60 ohms.

    So :  1/R = 1/60 + 23/1290 = (43+46) /2580 = 89/2580

     R = 2580/89 = 29 ohms approx