f.5 phy－thhzpvx的部落格

標題:

f.5 phy

發問:

l---------------6V 電池---------------------------------llxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxllxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxll----電阻(R)----3個燈泡并聯(2V 4W/個)---------lin the about circuit,the light bulbs are identical,each marked 2V 4W .if the light bulbs are to be worked as rated,the... 顯示更多 l---------------6V 電池---------------------------------l lxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxl lxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxl l----電阻(R)----3個燈泡并聯(2V 4W/個)---------l in the about circuit,the light bulbs are identical,each marked 2V 4W .if the light bulbs are to be worked as rated,the resistance of the resistor R should be ??(詳細答案^^)

最佳解答:

by P = V^2 / R 先計一計每個燈泡的resistance. putting P = 4, V = 2 we have, 4 = 2^2 / R R = 4 / 4 = 1 ohm then, 因3個燈泡是並聯, 故它們的equivalent resistance = 1/ [1/1 + 1/1 + 1/1] (by equivalent R = 1/ [1/R + 1/R' + 1/R''] ) = 1 / 3 ohm 然後, 流通每一個燈泡的電流是 = 4 / 2 (by P = V x I) = 2 A 因3個燈泡是並聯,so main current 是2 + 2 + 2 = 6 A so, consider the main power supply and the main current, by V = I x R 6 = 6 x R R = 1 ohm 所以main resistance is 1 ohm 因電阻是與因3個燈泡串聯, 故main R = R + equivalent R of 3個燈泡 1 = R + 1/3 R = 2/3 ohm

其他解答:

R=2^2/4=1 So R of 3 bulb is 3 ohm 6=R+3 R=3 ohm