能源問(wèn)題是當(dāng)前的熱門(mén)話題，傳統(tǒng)的能源——煤和石油，一方面儲(chǔ)量有限，有朝一日將要被開(kāi)采完畢，另一方面，使用過(guò)程中也帶來(lái)了污染，尋找新的、無(wú)污染的能源是人們努力的方向，利用潮汐發(fā)電即是一例.

關(guān)于潮汐，古人說(shuō)：“潮者，據(jù)朝來(lái)也；汐者，言夕至也.”圖10-6-1是利用潮汐發(fā)電的示意圖.左方為陸地和海灣，中間為大壩；其下有通道，水經(jīng)通道可帶動(dòng)發(fā)電機(jī).漲潮時(shí)，水進(jìn)入海灣，待內(nèi)外水面高度相同，堵住通道［圖10-6-1(甲)］，潮退至最低點(diǎn)時(shí)放水發(fā)電［圖10-6-1(乙)］；待內(nèi)外水面高度相同；再堵住通道，直到下次漲潮至最高點(diǎn)，又放水發(fā)電［圖10-6-1(丙)］.設(shè)海灣面積為5.0×107 m2，高潮與低潮間高度差3.0 m，則一天內(nèi)水流的平均功率為_(kāi)____MW.

圖10-6-1

(注：實(shí)際上由于各種損失，發(fā)電功率僅為水流的平均功率的10%—25%.例如法國(guó)蘭斯河(the Rance River)潮汐發(fā)電站水勢(shì)能釋放平均功率240 MW，而發(fā)電功率僅為62 MW)

解析：潮汐發(fā)電其實(shí)就是將海水的重力勢(shì)能轉(zhuǎn)化為電能.

    每次漲潮時(shí)流進(jìn)海灣(落潮時(shí)流出海灣)的海水的重力為：

    Mg=ρVg=1.0×103×5.0×107×3×10 N=1.5×1012 N

    其重心的高度變化為：h=1.5 m

    一天內(nèi)海水兩進(jìn)兩出，故水流功率為：

    P= W≈1.0×108 W

    即P≈100 MW.

答案：100


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