Trainee - Advice please

[matt1386]

Hi all, sorry if this is in the wrong section, wasnt too sure where to post it

Basically ive started college a few weeks late so im having to play catch up at home to get to where the rest of the class are at

Ive come across a question on my work sheet which im not sure how to work out and wondered if you could advise me, im not asking for the answer, just how to work it out

Here is the worksheet :

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My questions are in relation to the second table

1. How do I work out the value of the unknown resistors ?
2. What does the - symbol mean in the R3 column ?

Thanks very much for any help, ive searched google but cant seem to find what im looking for

 

[Marvo]

If you're in the process of training you can apply for access to our trainee forum which is custom made for this type of thread. Have a read of this post and do the necessary and you'll be given access if you qualify.

The symbol in the R3 column indicates that there is no R3 in that particular circuit.

The formula you need is; RT = 1/{(1/R1)+(1/R2)+(1/R3)...+(1/ Rad infinitum)...}

 

[matt1386]

Thank you very much Marvo, thats really appreciated

Will have a read of that thread now

thanks again

Matt

 

[Sintra]

To find R2 if you have R1 & Rt use this formula

R2 = R1 x Rt / R1 + Rt

as Marvo says the symbol just means there is no value in that column.

 

[matt1386]

Thanks Sintra, appreciate the help and support

So the missing value in row a would be 96 ohms is that correct ? and b would be 24 ohms ?

Thanks again guys

 

[Sintra]

Row A = 80 ohms

120 x 48 = 5760
120 - 48 = 72
5760 / 72 = 80

Row B = 16 ohms

48 x 12 = 576
48 - 12 = 36
576 / 36 = 16

 

[matt1386]

Ahh got it, thanks for that sintra, appreciated