Wheatstone Bridge Bench
Wheatstone Bridge Bench
Find an unknown resistor X by balancing the bridge. When the needle sits on zero, X = R × Q ÷ P.
1
Pick a resistor to find
2
Slide R until the needle stands at 0
R (the resistor you can change)
0 Ω
−10
−1
+1
+10
Needle (galvanometer)
Voltage at the two middle points
0 V
0 V
Point B
Point D
3
Work out X
Check X with a meter
---- Ω
Save to table
Why does this work?
Two paths
Current from the cell splits: one path through P and Q, the other through R and X.
Same height
When points B and D have the same voltage, no current crosses the needle. It reads 0. This is called balance.
The rule
At balance P ÷ Q = R ÷ X, so X = R × Q ÷ P. You can find X without measuring it directly.
My readings
Unknown
P (Ω)
Q (Ω)
R at balance (Ω)
X = R × Q ÷ P (Ω)
Meter (Ω)