Resistanse

[None]

Ok, I got a wierd questions about resistance.

In the picture bellow, I got a problem that I can not figure out how/or if its posible.

The thing is, I wish to have between 1-4: 9ohm, and between 2-4: 9 ohm. BUT I can only connect more resistance on the cable and not inside. Is there away for me to add more resistance on the cable that will make it 9ohm between both?

This problem has been bugging me for ages, sense I studied to be become a Electrician.

 

[topquark]

Given the constraint of only adding resistance to the cable then no, you can't. You could cheat and have a variable resistance of 0-4.7 ohm and change the resistance between measurements, but that would be cheating

 

[None]

Given the constraint of only adding resistance to the cable then no, you can't. You could cheat and have a variable resistance of 0-4.7 ohm and change the resistance between measurements, but that would be cheating

Not the answer i wanted, some how in my head there should be a way to dubble the resistance so high and after that halfing it down, so it will somehow become near 9 ohm.

 

[ringer]

Why can't you put another 4.7 ohms on the branch at point 2?

 

[topquark]

If point 2 is cable and not just a measurement point, then yes, that'd do it.

 

[DiscoDave]

you'll have to explain the application and what is inside and outside of it, ie which bit is the cable?

edit; sorry worked out what you mean now, but still interested in the application

 

[Golden_Boy]

4.7 + 4.7 = 9.4

Where did you get the 9.0 from?

 

[mikeymoo]

you add a 4.7 in series at position 2

 

[None]

4.7 + 4.7 = 9.4

Where did you get the 9.0 from?

sayd ~9 ohm, as near it as posible.

 

[mikeymoo]

between 1 + 4 you will get a 9.4 ohms and you could put a 4.3 ohm resistor at point 2. This will give you 9 ohms between 1 + 2.

 

[mikeymoo]

or if you wanted to have both 9 ohms between 1+4 and 9 ohms between 1+2 you could add 4.2 Ω at point 2 this would put the resistor in series between point 1 and 2 giving 9 Ω, and a 50 Ω between 1 and 2 (parallel) giving you a reading of 9 Ω between 1 and for 4.

 

[None]

between 1 + 4 you will get a 9.4 ohms and you could put a 4.3 ohm resistor at point 2. This will give you 9 ohms between 1 + 2.

I sayd that I cant change anything inside there, only on the cable.

so like 4.7 ohm should be 9 ohm, and 9 ohm should still be around 9 ohm. so it should be still 9 ohm between 1-4 and then 9 ohm between 2-4 really really hard to figure out if its posible, so please take all your brains to work and make it happen!

 

[Mark42]

I don’t quite understand the question, or what level this problem is aimed at.

If you’re looking for precision, remember you can reduce the overall resistance of a fixed circuit by adding resistance in parallel, using the formula 1/R = 1/R1 + 1/R2 …

So for example, to reduce 9.4 ohms to 9.0 ohms add a resistance of 211.5 ohms in parallel.

(I think I worked it out right – it’s late )

Of course these are theoretical values, no such physical fixed resistors exist in reality, and such precision would rarely matter.

 

[Mark42]

...and a 50 Ω between 1 and 2 (parallel) giving you a reading of 9 Ω …

I don't understand.

A 4.7Ω in parallel with a 50Ω is 4.3Ω

1/x = 1/4.7 + 1/50

1/x = 0.2127 + 0.0200 = 0.2327

x = 1/0.2327 = 4.2974 ohms