Через участок цепи (см. рис.) идёт постоянный ток. Сила тока I = 8 А. Какую силу тока показывает амперметр? Сопротивление амперметра не учитывайте.

The total resistance of the circuit is R_total = r + r + r + (r * 3r) / (r + 3r) = 3r + 3r^2 / 4r = 3r + 3r/4 = 15r/4. The current through the ammeter is the total current I = 8 A. The ammeter measures the current flowing through the branch with resistance r. The voltage across the parallel branches is V_parallel = I_total * R_parallel, where R_parallel = (r * 3r) / (r + 3r) = 3r/4. The current through the ammeter is I_ammeter = V_parallel / r = (I_total * R_parallel) / r = (8 A * 3r/4) / r = 8 A * 3/4 = 6 A.