✔ 最佳答案
68. Max power at R occurs when R equals to the internal resistance r (say) of the battery. Thus, when curve (b) is at its peak, the power delivered at R must equal to the power delivered at r. Thus the "height" of the peak pf curve (b) should be half of that of curve (a) at that point. Thereofre, option A is the correct answer.
In option B, the power delivered to R at the peak of curve (b) is higher than the power delivered to the internal resistance r of the battery. Given that the current through R and r are equal, such situation is physically not possible.
69. It is laready shown clearly on the circuit diagram that the two wires are NOT connected together at the centre of the square. The current flow as indicated by the "red-line" is not possinle.
80. Statement (2) is true.
81. A voltage follower is an extremely simple circuit that simply outputs a low impedance voltage that is identical to the input.
You may refer to the following web-page for more information:
http://electroniccircuitsforbeginners.blogspot.com/2009/05/voltage-follower-circuit.html
2011-12-08 09:07:19 補充：
69. Yes, the "semi-circle" symbol indicates that the two wires are not connected. If they are connected, then there is a "short-circuit". The equivalent resistance is zero.
2011-12-08 09:10:48 補充：
80. The statement has already explained itself. If the Neutral pin is connected to the Live wire in the socket, because the Neutral pin is also connected to the metal case, that makes the case carries a high potential. Once it is touched, this would cause an electric shock.
