How do I find the value of resistor 4? [closed]

Assuming this is balanced: if R1 is 130 Ω, R2 is 240 Ω, and R3 is 65 Ω, then what is R4?

• Think about it yourself. If "Assuming this is balanced" is given, what is the consequence for the voltage Vout = Vc - Vd?
– Uwe
Apr 25, 2023 at 23:46
• So would it be proportionate? Why does it do this? Apr 26, 2023 at 0:02
• assume that Vs = 10 V ... what is Vc ... what would be Vc if the resistors were 2× the value? Apr 26, 2023 at 0:05
• So R4 would equal 120 ohms? Does the word “balanced” in this situation mean that Vout is equal to 0? Apr 26, 2023 at 0:17
• yes a balanced bridge has $V_{Out }= 0$ Apr 26, 2023 at 1:00

2 Answers

If it's balanced VC = VD

So the ratio R1:R2 matches the ratio R3:R4

or if it's easier R1:R3 matches R2:R4

If as others have suggested "balanced" means Vc - Vd = 0, then the voltage drop across R1 and R3 must be equal, as they are connected to the same voltage on their other end. Likewise for R2 and R4. Convince yourself using algebra that the only way this is possible is if the ratio of R1 / R2 and R3 / R4 are the same.