Total resistance in a circuit question

[mtig]

Homework Statement

Assuming the wires have negligible resistance, find the equivalent resistance between the terminals A and B. Answer to 2 significant figures.

Homework Equations

[/B]
1/R = 1/R₁ + 1/R₂ ... + 1/R_n

R = R₁ + R₂ + R_n

The Attempt at a Solution

[/B]
I have drawn a more simplified circuit on a piece of paper and as the horizontal wire in the middle of the circuit has no resistance I have ignored the 4 resistor below it as no current will travel through them.

I have used the resistor equations above but I can't get the right answer. It is an online question and it will only tell me if the answer is right or wrong.

Any help will be appreciated.

Thanks

 

[gneill]

Show the details of your calculation attempt.

 

[mtig]

I added up the resistors in series (6 + 7) = 13

Then the two in parallel (1/10 + 1/5) = 3/10 Therefore resistance in parallel = 10/3 = 3.33

= 16 ohms

 

[gneill]

I added up the resistors in series (6 + 7) = 13

Then the two in parallel (1/10 + 1/5) = 3/10 Therefore resistance in parallel = 10/3 = 3.33

= 16 ohms

Ah. Well the 6 and 7 Ohm resistors are not in series. The B terminal is joined to the junction where they meet, so that junction is not unique to just the two resistors. The B terminal has to be considered a path that current can take since it's part of where you're "measuring" the circuit resistance from.

The 5 and 10 Ohm resistors are in parallel though, so that calculation is fine. Redraw the circuit with them replaced by a single resistor and continue to simplify from there.

 

[mtig]

Thank you very much I've got the right answer now.

I did 1/(3.33 + 6) + 1/7 = 0.25 Therefore resistance = 4 Ohms

I sort of get where I went wrong but I'm still getting my head round it.