如圖8所示,某同學(xué)采用雙線擺和光電計(jì)數(shù)器測(cè)量重力加速度.已知每根懸線長(zhǎng)l,兩懸點(diǎn)間相距s,金屬小球半徑為r,AB為光電計(jì)數(shù)器.現(xiàn)將小球垂直于紙面向外拉動(dòng),使懸線偏離豎直方向一個(gè)較小的角度并由靜止釋放,同時(shí)啟動(dòng)光電計(jì)數(shù)器,當(dāng)小球第一次經(jīng)過(guò)圖中虛線(光束)位置O時(shí),由A射向B的光束被擋住,計(jì)數(shù)器計(jì)數(shù)一次,顯示為“
1”,同時(shí)由零開(kāi)始計(jì)時(shí),而后每當(dāng)小球經(jīng)過(guò)O點(diǎn)時(shí),計(jì)數(shù)器都要計(jì)數(shù)一次.當(dāng)計(jì)數(shù)器上顯示的計(jì)算次數(shù)剛好為n時(shí),計(jì)時(shí)時(shí)間為t.由此可知雙線擺的振動(dòng)周期T為_(kāi)______;計(jì)算重力加速度g時(shí),雙線擺的等效擺長(zhǎng)L為_(kāi)______;最后依據(jù)公式g=_______,代入周期T和等效擺長(zhǎng)L的值即可求出重力加速度.?
圖8