Tsab xov xwm hais txog kev tsim duab los ntawm lub lens sib sau ua ke (convex)
Yuav kom nkag siab txog kev tsim duab los ntawm lub lens convex, kawm cov piv txwv ntawm cov teeb meem thiab cov kev daws teeb meem hauv qab no. Hauv qhov no, qhov khoom raug xav tias nyob ntawm qhov deb ntawm lub lens convex,
ces kos cov duab tsim los ntawm lub lens convex, qhov deb ntawm daim duab los ntawm lub lens convex thiab qhov loj ntawm daim duab los ntawm lub lens convex.
Lub lens convex muaj qhov ntev focal ntawm 20 cm. Cov khoom uas muaj qhov siab ntawm 10 cm nyob rau sab laug ntawm lub lens. Txheeb xyuas qhov deb ntawm daim duab, qhov loj ntawm daim duab thiab qhov siab ntawm daim duab, yog tias:
a) qhov deb ntawm lub lens convex me dua qhov ntev ntawm lub lens convex (do < f),
b) qhov deb ntawm lub lens convex yog tib yam li qhov ntev ntawm lub lens convex (do = f),
c) qhov deb ntawm lub lens convex loj dua qhov ntev ntawm lub lens convex (do > f).
Paub:
Qhov ntev ntawm lub lens convex (f) = 20 cm
Qhov ntev ntawm lub lens convex yog kos npe zoo vim tias qhov chaw ntawm lub lens convex yog qhov tseeb, qhov twg lub teeb hla dhau qhov chaw.
Qhov siab ntawm yam khoom (h) = 10 cm
tshuaj:
Qhov nrug ntawm yam khoom me dua qhov ntev ntawm lub lens convex (do > f)
Xav tias qhov nrug ntawm yam khoom yog 5 cm, 10 cm thiab 15 cm.
a) Yog tias qhov deb ntawm yam khoom (do) = 5 cm
Qhov nrug ntawm daim duab (di)
1/di = 1/f – 1/do = 1/20 – 1/5 = 1/20 – 4/20 = -3/20
ntawm = -20/3 = -6.7 cm
Qhov nrug ntawm daim duab yog negative, txhais tau tias daim duab yog virtual, qhov twg lub teeb tsis hla dhau daim duab.
Qhov nrug ntawm daim duab yog 6.7 cm, siab dua qhov nrug ntawm yam khoom 5 cm.
Qhov loj ntawm daim duab (M)
M = -di / ua = -(-6.7) / 5 = 6.7 / 5 = 1.3
Qhov loj ntawm daim duab tshaj 1 txhais tau tias qhov loj ntawm daim duab loj dua qhov loj ntawm yam khoom.
Qhov siab ntawm daim duab (hi)
Cov qauv ntawm daim duab loj dua:
M = hi / ho
hi = M ho = (1.3)(10 cm) = 13 cm
Qhov siab ntawm daim duab, kos npe zoo, txhais tau tias daim duab sawv ntsug.
b) Yog tias qhov deb ntawm yam khoom (ua) = 10 cm
Qhov nrug ntawm daim duab (di)
1/di = 1/f – 1/do = 1/20 – 1/10 = 1/20 – 2/20 = -1/20
ntawm = -20/1 = -20 cm
Qhov nrug ntawm daim duab yog negative txhais tau tias daim duab yog virtual, qhov twg lub teeb tsis hla dhau daim duab.
Qhov nrug ntawm daim duab 20 cm loj dua qhov nrug ntawm yam khoom 10 cm.
Qhov loj ntawm daim duab (M)
M = -di / ua = -(-20)/10 = 20/10 = 2
Qhov loj ntawm daim duab tshaj 1 txhais tau tias qhov loj ntawm daim duab loj dua qhov loj ntawm yam khoom.
Qhov siab ntawm daim duab (hi)
Cov qauv ntawm kev loj hlob ntawm daim duab:
M = hi / ho
siab = M h = (2)(10 cm) = 20 cm
Qhov siab ntawm daim duab yog positive uas txhais tau tias daim duab ncaj.
c) Yog tias qhov deb ntawm yam khoom (ua) = 15 cm
Qhov nrug ntawm daim duab (di)
1/di = 1/f – 1/do = 1/20 – 1/15 = 3/60 – 4/60 = -1/60
ntawm = -60/1 = -60 cm
Qhov nrug ntawm daim duab yog negative txhais tau tias daim duab yog virtual, qhov twg lub teeb tsis hla dhau daim duab.
Qhov nrug ntawm daim duab 60 cm loj dua qhov nrug ntawm yam khoom 15 cm.
Qhov loj ntawm daim duab (M)
M = -di / ua = -(-60)/15 = 60/15 = 4
Qhov loj ntawm daim duab tshaj 1 txhais tau tias qhov loj ntawm daim duab loj dua qhov loj ntawm yam khoom.
Qhov siab ntawm daim duab (hi)
Cov qauv ntawm kev loj hlob ntawm daim duab:
M = siab / teev
siab = M h = (4)(10 cm) = 40 cm
Qhov siab ntawm daim duab yog qhov zoo txhais tau tias daim duab sawv ntsug.
Qhov nrug ntawm cov khoom yog sib npaug rau qhov ntev ntawm lub lens convex (do = f)
Daim duab nyob ntawm qhov deb tsis kawg.
Qhov nrug ntawm yam khoom loj dua qhov ntev ntawm lub lens convex (do > f)
Xav tias qhov nrug ntawm yam khoom yog 30 cm, 40 cm thiab 50 cm.
a) Yog tias qhov deb ntawm yam khoom (do) = 30 cm
Qhov nrug ntawm daim duab (di)
1/di = 1/f – 1/do = 1/20 – 1/30 = 3/60 – 2/60 = 1/60
di = 60/1 = 60 cm
Qhov nrug ntawm daim duab yog qhov zoo, txhais tau tias daim duab yog qhov tseeb, qhov twg lub teeb ci ntsa iab dhau los ntawm daim duab.
Qhov nrug ntawm daim duab 60 cm loj dua qhov nrug ntawm yam khoom 30 cm.
Qhov loj ntawm daim duab (M)
M = -di / ua = -60/30 = -2
Daim duab loj dua 1, txhais tau tias daim duab loj dua qhov loj ntawm yam khoom.
Qhov siab ntawm daim duab (hi)
Cov qauv ntawm kev loj hlob ntawm daim duab:
M = siab / teev
siab = M h = (-2)(10 cm) = -20 cm
Qhov siab ntawm daim duab yog lub cim tsis zoo txhais tau tias daim duab tig rov qab.
b) Yog tias qhov deb ntawm yam khoom (ua) = 40 cm
Qhov nrug ntawm daim duab (di)
1/di = 1/f – 1/do = 1/20 – 1/40 = 2/40 – 1/40 = 1/40
di = 40/1 = 40 cm
Qhov nrug ntawm daim duab yog qhov zoo, txhais tau tias daim duab yog qhov tseeb, qhov twg lub teeb ci ntsa iab dhau los ntawm daim duab.
Qhov nrug ntawm daim duab yog 40 cm, sib npaug rau qhov nrug ntawm yam khoom yog 40 cm.
Qhov loj ntawm daim duab (M)
M = -di / ua = -40/40 = -1
Qhov loj ntawm daim duab yog 1 txhais tau tias qhov loj ntawm daim duab sib npaug rau qhov loj ntawm yam khoom.
Qhov siab ntawm daim duab (hi)
Cov qauv ntawm kev loj hlob ntawm daim duab:
M = hi / ho
siab = M h = (-1)(10 cm) = -10 cm
Qhov siab ntawm daim duab yog negative txhais tau tias daim duab tig rov qab.
b) Yog tias qhov deb ntawm yam khoom (ua) = 50 cm
Qhov nrug ntawm daim duab (hauv)
1/di = 1/f – 1/do = 1/20 – 1/50 = 5/100 – 2/100 = 3/100
di = 100/3 = 33.3 cm
Qhov nrug ntawm daim duab yog qhov zoo, txhais tau tias daim duab yog qhov tseeb, qhov twg lub teeb ci ntsa iab dhau los ntawm daim duab.
Qhov nrug ntawm daim duab 33.3 cm me dua qhov nrug ntawm yam khoom 50 cm.
Kev loj ntawm daim duab (M) Av
M = -di / ua = -33.3/40 = -0.8
Qhov loj ntawm daim duab me dua 1, txhais tau tias qhov loj ntawm daim duab me dua qhov loj ntawm yam khoom.
Qhov siab ntawm daim duab (nyob zoo)
Cov qauv ntawm kev loj hlob ntawm daim duab:
M = siab / teev
siab = M h = (-0.8)(10 cm) = -8 cm
Qhov siab ntawm daim duab yog qhov tsis zoo, txhais tau tias daim duab tig rov qab.
