Resistive circuit - ladder problem

lundi 1 septembre 2014

Hey!

1. The problem

Figure shows a very long ladder where every part has a resistanse of R. What is the resistance between A and B if the ladder can be approximated to be semi-infinite (the ladder has a beginning but no end).





2.The figure







3. The attempt

The first three resistances have a resistance of 3R the next step add 3R in paralell to R. The next step after that provides 3 more resistances in paralell with on of the resistances in step two.



Step 1: 3R

Step 2: ##\frac{3R \cdot R}{R+3R}+2R=\frac{3R}{4}+\frac{8R}{4}=\frac{11R}{4}##

Step 3: ##\frac{11R}{4}+2R=\frac{19R}{4}##

Step 4: ##\frac{19R}{4}+2R=\frac{27R}{4}##

Step 5: ##\frac{27R}{4}+2R=\frac{35R}{4}##



I am not sure if I am doing this right. My resistance gets bigger for ever step that I add(the resistance should be lower and lower for every step). It feels like I have missed the point of this problem. Please help me.





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