Tsab xov xwm hais txog kev tsim duab los ntawm lub lens diverging (concave lens)
Yuav kom nkag siab txog kev tsim duab los ntawm lub lens concave, saib cov piv txwv teeb meem thiab kev daws teeb meem hauv qab no. Hauv qhov no, qhov khoom raug xav tias nyob ntawm qhov deb ntawm lub lens concave,
tom qab ntawd kos cov duab tsim los ntawm lub lens concave, qhov deb ntawm daim duab los ntawm lub lens concave thiab qhov loj ntawm daim duab los ntawm lub lens concave.
Qhov ntev ntawm lub lens concave (lub lens diverging) yog 20 cm. Cov khoom uas siab 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 yam khoom me dua qhov ntev ntawm lub lens concave
b) qhov deb ntawm cov khoom yog tib yam li qhov ntev ntawm lub lens concave
c) qhov deb ntawm yam khoom loj dua qhov ntev ntawm lub lens concave
Paub:
Qhov ntev ntawm lub lens concave (f) = -20 cm
Qhov ntev ntawm lub lens concave muaj lub cim tsis zoo vim tias qhov chaw ntawm lub lens concave yog virtual, qhov twg lub teeb ci tsis dhau los ntawm qhov chaw.
Qhov siab ntawm yam khoom (h) = 10 cm
tshuaj:
Qhov deb ntawm yam khoom me dua qhov ntev ntawm lub lens concave (do > f)
Xav tias qhov nrug ntawm yam khoom yog 5 cm, 10 cm thiab 15 cm.
a) Qhov ntev ntawm lub focal yog -20 cm thiab 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 = -5/20
ntawm = -20/5 = -4 cm
Lub cim qhia qhov deb ntawm daim duab, tsis zoo, txhais tau tias daim duab yog virtual, qhov twg lub teeb tsis hla dhau daim duab.
Qhov nrug ntawm daim duab, 4 cm, me dua qhov nrug ntawm yam khoom, 5 cm.
Qhov loj ntawm daim duab (M)
M = -di / ua = -(-4)/5 = 4/5 = 0.8
Qhov kev loj ntawm daim duab me dua 1 txhais tau tias daim duab raug txo qis, lossis qhov loj ntawm daim duab me dua qhov loj ntawm yam khoom.
Qhov siab ntawm daim duab (h')
Cov qauv ntawm kev loj hlob ntawm daim duab:
M = h' / h
h' = M h = (0.8)(10 cm) = 8 cm
Qhov siab ntawm daim duab yog ib qho cim zoo, txhais tau tias daim duab sawv ntsug.
b) Qhov ntev ntawm lub focal yog -20 cm thiab yog tias qhov deb ntawm yam khoom (do) = 10 cm
Qhov nrug ntawm daim duab (di)
1/di = 1/f – 1/do = -1/20 – 1/10 = -1/20 – 2/20 = -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, me dua qhov nrug ntawm yam khoom, 10 cm.
Qhov loj ntawm daim duab (M)
M = -di / ua = -(-6.7)/10 = 6.7 / 10 = 0.67
Qhov loj ntawm daim duab me dua 1 txhais tau tias daim duab raug txo qis, lossis qhov loj ntawm daim duab me dua qhov loj ntawm yam khoom.
Qhov siab ntawm daim duab (h')
Cov qauv ntawm kev loj hlob ntawm daim duab:
M = h'/h
h' = M h = (0.67)(10 cm) = 6.7 cm
Qhov siab ntawm daim duab yog ib qho cim zoo, txhais tau tias daim duab sawv ntsug.
c) Qhov ntev ntawm lub focal yog -20 cm thiab qhov deb ntawm yam khoom (do) = 15 cm
Qhov nrug ntawm daim duab (di)
1/di = 1/f – 1/do = -1/20 – 1/15 = -3/60 – 4/60 = -7/60
ntawm = -60/7 = -8.6 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 8.7 cm, me dua qhov nrug ntawm yam khoom, 15 cm.
Qhov loj ntawm daim duab (M)
M = -di / ua = -(-8.6)/10 = 8.6 / 10 = 0.86
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 (h')
Cov qauv ntawm kev loj hlob ntawm daim duab:
M = h'/h
h' = M h = (0.86)(10 cm) = 8.6 cm
Qhov siab ntawm daim duab yog qhov zoo, txhais tau tias daim duab yog ntsug.
Qhov nrug ntawm cov khoom yog tib yam li qhov ntev ntawm lub lens concave (do = f)
Qhov ntev ntawm lub tsom iav (f) = qhov nrug ntawm yam khoom (do) = 20 cm.
Qhov nrug ntawm daim duab (di)
1/di = 1/f – 1/do = -1/20 – 1/20 = -2/20 = -2/20
ntawm = -20/2 = -10 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 10 cm, me dua qhov nrug ntawm yam khoom, 20 cm.
Qhov loj ntawm daim duab (M)
M = -di / ua = -(-10)/20 = 10/20 = 0.5
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 (h')
Cov qauv ntawm kev loj hlob ntawm daim duab:
M = h'/h
h' = M h = (0.5)(10 cm) = 5 cm
Qhov siab ntawm daim duab yog qhov zoo, txhais tau tias daim duab yog ntsug.
Qhov nrug ntawm yam khoom loj dua qhov ntev ntawm lub lens concave (do > f)
Xav tias qhov deb ntawm cov khoom yog 30 cm thiab 40.
a) Qhov ntev ntawm lub focal yog -20 cm thiab 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 = -5/60
ntawm = -60/5 = -12 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 12 cm, me dua qhov nrug ntawm yam khoom yog 30 cm.
Qhov loj ntawm daim duab (M)
M = -di / ua = -(-12)/30 = 12/30 = 0.4
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 (h')
Cov qauv ntawm kev loj hlob ntawm daim duab:
M = h'/h
h' = M h = (0.4)(10 cm) = 4 cm
Qhov siab ntawm daim duab yog ib qho cim zoo, txhais tau tias daim duab sawv ntsug.
b) Qhov ntev ntawm lub focal -20 cm thiab yog tias qhov deb ntawm yam khoom (do) = 40 cm
Qhov nrug ntawm daim duab (di)
1/di = 1/f – 1/do = -1/20 – 1/40 = -2/40 – 1/40 = -3/40
ntawm = -40/3 = -13 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 13 cm, me dua qhov nrug ntawm yam khoom yog 40 cm.
Qhov loj ntawm daim duab (M)
M = -di / ua = -(-13)/40 = 13/40 = 0.3
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 (h')
Cov qauv ntawm kev loj hlob ntawm daim duab:
M = h'/h
h' = M h = (0.3)(10 cm) = 3 cm
Qhov siab ntawm daim duab yog kos npe rau qhov zoo, txhais tau tias daim duab yog ntsug.
