✔ 最佳答案
175. Current = 9/(1 + 2 + 3) A = 1.5 A The current is flowing anti-clockwise round the circuit.voltage across 2-ohm resistor = 1.5 x 2 v = 3 vhence, potential at b = +3 vvoltage across 1-ohm resistor = 1.5 x 1 v = 1.5 vhence, potential at a = (1.5+3) v = +4.5 vstatement (1) is wrong voltage across 3-ohm resistor = 1.5 x 3 v = 4.5 vhence, potential at d = -4.5 vstatement (2) is correct voltage between b and d = [+3 – (-4.5)] v = 7.5 vstatement (3) is correct. 176. current in the circuit = (3+3)/(1+2) A = 2 A notice that the current is flowing anti-clockwise round the circuitvoltage at b = -3 vvoltage across 1-ohm resistor = 2 x 1 v = 2 vhence, potential at a = [2 + (-3)] v = -1 v voltage across 2-ohm resistor = 2 x 2 v = 4 vhence, potential at d = -4 vpotential difference between b and d = [(-3) – (-4)] v = 1 v Therefore, the answer is option C
2011-04-27 08:56:14 補充：
Earthing makes the potential at the "earthing point" to become zero ( 0 volt). From this point, you could proceed to calculate the potentials at other points.
2011-04-27 08:57:44 補充：
Remember that if you go with the direction of current, potential will decrease when passing a resistor. It is because current flows from point of high potential to point of low potential....
2011-04-27 08:58:44 補充：
Likewise, if you go AGAINST the current (i.e. in opposite direction to current), the potential will increase after passing through a resistor.
