Find Current Through Battery in Circuit: 3/11 or 21/19?

[giokrutoi]

Homework Statement

the image of circuit is in attachment
the question is to find the current through the battery

Homework Equations

The Attempt at a Solution

I think that there is a y connection
so above two and centered one form y from formula the whole resistance is 1
than I imagine bottomed ones and this and above ones as new y type connection and
I get 1/R = 1/(1/1 + 1/2 + 1/3) and r is equal to 11
all in all the current should be I=U/R = 3/11
but in book the answer is 21/19
please help

 

[timetraveller123]

you can use delta to y conversion

 

[gneill]

I think that there is a y connection
so above two and centered one form y from formula the whole resistance is 1

Please show the formula used and the details of how you applied it for your Y to Δ transformation. What do you mean by the "whole resistance is 1"?

 

[timetraveller123]

this is the your current equivalent circuit you could change it to the form of

using
sorry for my poor drawing skills

 

[giokrutoi]

1/R = 1/(1/r1+1/r2+ 1/r3)

 

[giokrutoi]

View attachment 206479
this is the your current equivalent circuit you could change it to the form of
View attachment 206480
using
sorry for my poor drawing skills

I don't get the second picture

 

[timetraveller123]

i am sorry i will draw again

the 3 and 2 are the same old resistors but R_a , R_b , R_c are resistances to be determined using the delta to y conversion hope this clears up
what i am saying is that this circuit is equivalent to the old circuit if proper values of resistance for a b and c are used

 

[timetraveller123]

1/R = 1/(1/r1+1/r2+ 1/r3)

i don't understand what formula that is

 

[lewando]

1/R = 1/(1/r1+1/r2+ 1/r3)

This is the formula for finding the equivalent resistance of 3 resistors in parallel. Not the delta-wye formula.