⚖️ Wheatstone bridge — a null method needs no calibrated meter

Four resistors in a diamond, a cell across one diagonal and a galvanometer across the other. When R₁/R₂ = R₃/R₄ the two midpoints sit at the same potential, so no current crosses the bridge at all — and an unknown resistance is read off the other three.

Walkthrough 1 / 4

Four resistors form a diamond and a cell drives current in at A and out at C — two parallel paths, A→B→C and A→D→C.

R₁ 10 Ω

R₂ 20 Ω

R₃ 10 Ω

R₄ (unknown) 14 Ω

Balance R₁/R₂ = R₃/R₄ → — vs —
I_g = — mA · balances at R₄ = R₂·R₃/R₁ = — Ω

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