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電的問題.... AL~
發問:
Q 1: 點解e-field lines 唔會相交? Q 2 : Charging a capacitor 係咪short circuit ? Q 3: AL 97MC #30 ( capacitor)? 點做?
最佳解答:
3. At steady state,P.D. across R1 = 6 X 6 / (6 + 3) = 4 V Hence, P.D. at A = 6 - 4 = 2 V Similarly, P.D. across R3 = 6 X 1 / (1 + 2) = 2 V P.D. at B = 6 - 2 = 4 V Hence, P.D. across AB = 2 - 4 = -2 V which the potential at B is higher than that at A. Hence, -ve charge is on the capacitor plate connecting A. By Q = CV Q = (20 X 10-6)(-2) Q = -40 X 10-6 C The answer is E. 2008-10-12 16:19:06 補充： 1. Electric force is a conservative force. There is a characteristic of a conservative force, i.e. the field will not form a loop. In other words, the electric field will not intersect each other. 2008-10-12 16:19:22 補充： The explanation is as follows: A charge is doing work when it travels along the field line. If the field lines form a loop, then the net work done by the charge to travel through a complete loop is not zero, which violates the definition of conservative force. 2008-10-12 16:19:27 補充： Hence, e-field lines will not intersect each other. 2008-10-12 16:19:39 補充： 2. I don't quite understand your question. In a steady D.C. circuit, when the circuit is completed, then the capacitor is being charged by a varying current. When the capacitor is being fully charged, then the circuit is open. 2008-10-12 16:19:44 補充： In a varying A.C. circuit, the impedance of a capacitor is given as 1 / (2 pifC), where f and C is the frequency of the source and the capacitance of the capacitor respectively. Hence, if the frequency becomes very large, then the capacitor can be regarded as a short-circuit.
電的問題.... AL~
發問:
Q 1: 點解e-field lines 唔會相交? Q 2 : Charging a capacitor 係咪short circuit ? Q 3: AL 97MC #30 ( capacitor)? 點做?
最佳解答:
3. At steady state,P.D. across R1 = 6 X 6 / (6 + 3) = 4 V Hence, P.D. at A = 6 - 4 = 2 V Similarly, P.D. across R3 = 6 X 1 / (1 + 2) = 2 V P.D. at B = 6 - 2 = 4 V Hence, P.D. across AB = 2 - 4 = -2 V which the potential at B is higher than that at A. Hence, -ve charge is on the capacitor plate connecting A. By Q = CV Q = (20 X 10-6)(-2) Q = -40 X 10-6 C The answer is E. 2008-10-12 16:19:06 補充： 1. Electric force is a conservative force. There is a characteristic of a conservative force, i.e. the field will not form a loop. In other words, the electric field will not intersect each other. 2008-10-12 16:19:22 補充： The explanation is as follows: A charge is doing work when it travels along the field line. If the field lines form a loop, then the net work done by the charge to travel through a complete loop is not zero, which violates the definition of conservative force. 2008-10-12 16:19:27 補充： Hence, e-field lines will not intersect each other. 2008-10-12 16:19:39 補充： 2. I don't quite understand your question. In a steady D.C. circuit, when the circuit is completed, then the capacitor is being charged by a varying current. When the capacitor is being fully charged, then the circuit is open. 2008-10-12 16:19:44 補充： In a varying A.C. circuit, the impedance of a capacitor is given as 1 / (2 pifC), where f and C is the frequency of the source and the capacitance of the capacitor respectively. Hence, if the frequency becomes very large, then the capacitor can be regarded as a short-circuit.
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