Khi dao dong tai O sdm pha hon tai M la 27rd Phi/ong t r i n h dao dong cua phan tuf vat chat tai O la: Uo(t) = asin27r Vdy chqn dap an C Cdu 38: K h i c6 hien ttfcrng quang dien xay te bao quang dien, ph6t bieu nao sau day la sai? A Giuf nguyen cLforng chum sAng kich thich va k i m loai dung lam catot, giam tan so cua anh sang kich thich t h i dong nang ban dau C L T C dai cua electron (electron) quang dien giam B GiCr nguyen chum sang kich thich, thay ddi k i m loai lam catot thi dong nang ban dau ciTc dai cua electron (electron) quang dien thay doi C Giuf nguyen t a n so cua anh sang kich thich va kim loai lam catot, tang cifcfng chum sang kich thich t h i dong nang ban dau c\Xc dai cua electron (electron) quang dien tSng D Giu" nguyen ctfcfng chum sang kich thich va kim loai dung lam catot, giam hiidc song cua anh sang kich thich t h i dong nSng ban dau CLfc dai cua electron (electron) quang dien tang Giai Theo dinh luat quang dien, c6 hien tiigrng quang dien xay te bao quang di?n, dong nang ban dau ciic dai ciia cac quang electron hoan toan khong phu thuoc vao ciicfng anh sang kich thich ma chi phu thuoc vao budfc song va tan so Vdy chgn dap an C Cdu 39: Tai hai diem A va B mot moi tri/dng truyen song c6 hai nguon song ket hop, dao dong cung phtrong vdri phifcfng trinh Ian lifc*t la UA = asincot va U B = asin((ot + i ) Biet van toe va bien song m5i nguon tao khong doi qua trinh song truyen Trong khoang giuTa A va B CO giao thoa song hai nguon tren gay Phan tuf vat chat tai trung diem cua doan AB dao dong vdfi bien bkng: A - B 2a C D a 18 GiSi Chi tigt thi TS D H , C D M6n VSt!(