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# Resistance in Circuits Question Help Needed! watch

1. In a circuit, a resistor of resistance R is found to have 5% too much resistance for the correct functioning of the circuit. What value resistor, in terms of R, needs to be placed in parallel with R in order to reduce the total resistance to the correct value?

Many thanks!
In a circuit, a resistor of resistance R is found to have 5% too much resistance for the correct functioning of the circuit. What value resistor, in terms of R, needs to be placed in parallel with R in order to reduce the total resistance to the correct value?

Many thanks!
2 resistors in parallel have a total resistance given by:

If you want the total resistance of the circuit to be 5% less (i.e. 95% that which it currently is) then you have the condition that:

Solving the above equation under this condition will give you the answer.
3. 1/R + 1/x = 1/(R/1.05)

and solve for x, I think.
4. (Original post by Prime Suspect)
2 resistors in parallel have a total resistance given by:

If you want the total resistance of the circuit to be 5% less (i.e. 95% that which it currently is) then you have the condition that:

Solving the above equation under this condition will give you the answer.
Only it's a bit ambiguous. Because if R is 5% more than the desired resistance, , then and so which is not the same as 0.95R.
1/R + 1/x = 1/(R/1.05)

and solve for x, I think.
So in this case x will be the answer?
6. (Original post by Prime Suspect)
2 resistors in parallel have a total resistance given by:

If you want the total resistance of the circuit to be 5% less (i.e. 95% that which it currently is) then you have the condition that:

Solving the above equation under this condition will give you the answer.
It is currently 5% too much dude, so it's effectively 105%.
Only it's a bit ambiguous. Because if R is 5% more than the desired resistance, , then and so which is not the same as 0.95R.
t is currently 5% too much dude, so it's effectively 105%.
Point taken thanks guys adjust method to incorporate this:

and want

hence

where

so finally

8. (Original post by Prime Suspect)
Point taken thanks guys adjust method to incorporate this:

and want

hence

where

so finally

No problem man So in the end what value resistor is it, in terms of R?
So in this case x will be the answer?
Yup!
No problem man So in the end what value resistor is it, in terms of R?
Well from rearranging you get:

hence the answer (R_2) is (hopefully!)

11. (Original post by Prime Suspect)
Well from rearranging you get:

hence the answer (R_2) is (hopefully!)

Kool thanks a lot man!

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