Wheatstone Bridge Balanced Condition: Zero Galvanometer Current

A Wheatstone bridge is balanced when the voltage difference between its two midpoints (D and B) is zero—i.e., the galvanometer reads zero. At balance:

• Resistance ratio: R₁/R₂ = R₃/R₄ (adjacent arms equal opposite arms).
• Current: I_g = 0 (no current through galvanometer).
• Voltage: V_D = V_B (equal potential at midpoints).

This allows precise measurement of an unknown resistance (e.g., R₃) by adjusting a known variable resistor (R₄) until balance is achieved: R₃ = R₂ × (R₄/R₁). The bridge's sensitivity depends on galvanometer precision and supply voltage stability.