(Lawv yuav tsum tau saib zoo li rog, dub crayons, rho tawm daim ntawv lo.) Cov lus qhia tej zaum yuav ntse nrog cov riam uas tib neeg whittle sticks. Vim hais tias chemistry yog ib tug hluas science thaum lub sij hawm, tib neeg xav graphite yog ib daim ntawv ntawm txhuas; yog li no lub npe muab rau xaum.
Vim li cas xaum lead hu ua lead?
Ntawm no yog lus dab neeg dab neeg: Tsis muaj txhuas hauv xaum. Hloov chaw, cov tub ntxhais yog tsim los ntawm cov ntxhia tsis muaj tshuaj lom hu ua graphite. Lub npe hu ua "miv xaum" yog vim muaj kev koom tes nrog keeb kwm nrog cov stylus ua los ntawm cov hlau lead nyob rau hauv ancient Rome.
Thaum twg lawv tau tshem cov hlau lead hauv xaum?
Vim lawv pheej yig dua, txawm tias muaj tshuaj lom. Txawm li cas los xij, koj yeej yuav tsis xav nqus ntawm "cov hmoov txhuas" yog tias nws muaj cov hmoov txhuas hauv nws. Qhov tseeb, cov xaum xaum tau ploj mus tsuas yog nyob rau xyoo pua 20th.
Puas tsim nyog siv lo lus lead rau xaum xaum?
Yog li, tus cwj mem tau yug los nrog lub hauv paus ntawm cov khoom graphite, uas tau paub thaum ntawd los ua cov hmoov txhuas dub. Cov kev lig kev cai ntawm kev hu sticks ntawm graphite "lead" tau dhau mus rau hnub no. … Vim li cas Koj Yuav Tsum Tau Siv 2 cwj mem nrog Scantron daim ntawv.
Lub ntsiab lus ntawm xaum xaum yog dab tsi?
Noun. 1. cwj mem lead - sib tov ntawm graphite nrog av nplaum nyob rau hauv sib txawv degrees ntawm hardness; cov cim cim nyob rau hauv ib tug cwj mem. coj. lead cwj mem - mem hluav uas muaj graphite ua tus cimkhoom.
