標題:
F.5 Physics power
發問:
ch.2321. There is a set [identical light bulbs R and S in parallel,an opened switch isplaced next to light bulb S]The set is connected to a constant voltage supply and a fixed resistor in series 1.If the switch is closed,what happen to the brightness of R ?i.e:2.Brightness= power ??3.(if... 顯示更多 ch.23 21. There is a set [identical light bulbs R and S in parallel,an opened switch is placed next to light bulb S] The set is connected to a constant voltage supply and a fixed resistor in series 1.If the switch is closed,what happen to the brightness of R ? i.e: 2.Brightness= power ?? 3.(if so)By Power=V x I, V decreses and I increases ? How to deduce the change of Power ?
此文章來自奇摩知識+如有不便請留言告知
最佳解答:
1. Let R be the resistance of each light bulb, and r be the resistance of the resistor. Hence, voltage across bulb R before switch is closed = V.[R/(R+r)] -------------- (1) where V is the voltage of the supply. After the switch is closed, the equivalent resistance of the two bulbs in parallel = R/2 Hence, total resistance of circuit = R/2 + r = (R+2r)/2 New voltage across each bulb = V.[(R/2)/(R+2r)/2] = V.R/(R+2r) ----------- (2) Therefore, comparing (1) and (2), it is clear that the new voltage across bulb R is smaller than before. Thus, the brightness of bulb R will reduce. 2. Brightness of a bulb can be taken as more or less proportional to its power consumption. 3. The argument is only vaild when the power is kept constant.
其他解答:
留言列表
