2 Piv txwv ntawm cov lus nug txog convex convex ob lub lens
1. Ob lub lens convex, txhua lub muaj qhov ntev focal ntawm 20 cm thiab 30 cm, muab tso ze ua ke, nrog qhov deb ntawm ob lub lens convex yog 70 cm. Ib yam khoom yog 30 cm nyob rau pem hauv ntej ntawm lub lens thawj. Txheeb xyuas qhov deb ntawm daim duab thiab qhov loj ntawm daim duab uas tsim los ntawm ob lub lens. lub lens convex tus!
Kev Sib Tham
Nws paub tias:
Qhov ntev ntawm lub lens convex thawj zaug (f)1) = +20 cm
Qhov ntev ntawm lub lens convex thib ob (f)2) = +30 cm
Qhov ntev ntawm lub lens convex yog qhov zoo vim tias lub teeb ci ntsa iab hla dhau qhov chaw ntawm lub lens convex.
Qhov nrug ntawm ob lub lens convex (l) = 50 cm
Qhov deb ntawm cov khoom los ntawm thawj lub lens convex (s1) = 30 cm
Qhov nrug ntawm yam khoom yog qhov zoo vim tias lub teeb ci ntsa iab los ntawm yam khoom.
Lus teb:
a) Qhov deb ntawm duab ntxoov ntxoo
Qhov deb ntawm daim duab uas tsim los ntawm thawj lub lens convex (qhov deb ntawm daim duab thawj):
1/s1' = 1/f1 – 1/s1
1/s1' = 1/20 – 1/30 = 3/60 – 2/60 = 1/60
s1' = 60/1 = 60 cm
Daim duab thawj zaug yog 60 cm ntawm lub lens convex 1.
Qhov nrug ntawm daim duab thawj zaug yog qhov zoo, txhais tau tias daim duab thawj zaug yog qhov tseeb, txhais tau tias nws muaj tiag tiag vim tias lub teeb ci ntsa iab hla dhau daim duab.
Qhov deb ntawm daim duab uas tsim los ntawm lub lens convex thib ob (qhov deb kawg ntawm daim duab):
Daim duab uas tsim los ntawm thawj lub lens convex raug suav hais tias yog ib yam khoom los ntawm lub lens convex thib ob. Qhov deb ntawm thawj daim duab / khoom los ntawm lub lens convex thib ob (s2) = qhov deb ntawm ob lub lens convex - qhov deb ntawm thawj daim duab los ntawm thawj lub lens convex = 70 cm - 60 cm = 10 cm.
1/s2' = 1/f2 – 1/s2
1/s2'= 1/30 – 1/10 = 1/30 – 3/30 = -2/30
s2' = -30/2 = -15 cm
Daim duab kawg yog 15 cm ntawm lub lens convex thib ob.
Qhov nrug kawg ntawm daim duab yog qhov tsis zoo, txhais tau tias daim duab kawg yog pseudo lossis cuav vim tias daim duab tsis dhau los ntawm lub teeb ci (daim duab kawg yog sab laug ntawm lub lens convex thib ob).
b) Kev ua kom daim duab loj dua
Kev nthuav dav ntawm daim duab los ntawm thawj lub lens convex:
m1 = -s1'/s1 = -60 cm/30 cm = -2 zaug
Lub lens convex ua rau daim duab loj dua 2 npaug ntawm qhov loj ntawm yam khoom.
Qhov kev loj ntawm daim duab nrog lub cim tsis zoo txhais tau tias daim duab tig rov qab.
Kev nthuav dav ntawm daim duab los ntawm lub lens convex thib ob:
m2 = -s2'/s2 = -(-15 cm)/10 cm = 15/10 = 1,5 zaug
Lub lens convex thib ob ua rau lub khoom loj dua (duab ntawm lub lens convex thawj zaug) los ntawm 1,5 npaug.
Tag nrho cov duab loj dua yog:
m = (m1)(m2) = (-2)(1,5) = -3 zaug
Daim duab kawg loj dua 3 npaug ntawm qhov loj ntawm yam khoom lossis qhov siab ntawm daim duab kawg siab dua 3 npaug ntawm qhov siab ntawm yam khoom. Tag nrho qhov loj me yog qhov tsis zoo txhais tau tias daim duab tig rov qab. (Daim duab kawg tig rov qab yog li daim duab kawg yuav tsum nyob rau sab laug ntawm lub lens convex thib ob).
2. Qhov nrug ntawm ob lub lens convex yog 100 cm. Ob lub lens convex txhua lub muaj qhov ntev focal ntawm 20 cm thiab 80 cm. Ib yam khoom yog 30 cm nyob rau pem hauv ntej ntawm lub lens thawj. Txheeb xyuas qhov nrug ntawm daim duab thiab qhov loj ntawm daim duab uas tsim los ntawm ob lub lens convex!
Kev Sib Tham
Nws yog paub :
Qhov nrug ntawm ob lub lens (l) = 100 cm
Qhov ntev ntawm lub lens convex thawj zaug (f)1) = 20 cm
Qhov ntev ntawm lub lens convex thib ob (f)2) = 80 cm
Qhov ntev ntawm lub lens convex yog qhov zoo vim tias lub teeb ci ntsa iab hla dhau qhov chaw ntawm lub lens convex.
Qhov deb ntawm cov khoom los ntawm thawj lub lens convex (s1) = 30 cm
Qhov nrug ntawm yam khoom yog qhov zoo vim tias lub teeb ci ntsa iab los ntawm yam khoom.
Jawb :
a) Qhov deb ntawm duab ntxoov ntxoo
Qhov deb ntawm daim duab uas tsim los ntawm thawj lub lens convex (qhov deb ntawm daim duab thawj):
1/s1' = 1/f1 – 1/s1
1/s1' = 1/20 – 1/30 = 3/60 – 2/60 = 1/60
s1' = 60/1 = 60 cm
Daim duab thawj zaug yog 60 cm ntawm lub lens convex 1.
Qhov nrug ntawm daim duab thawj zaug yog qhov zoo, txhais tau tias daim duab thawj zaug yog qhov tseeb, txhais tau tias nws muaj tiag tiag vim tias lub teeb ci ntsa iab hla dhau daim duab.
Qhov deb ntawm daim duab uas tsim los ntawm lub lens convex thib ob (qhov deb kawg ntawm daim duab):
Daim duab uas tsim los ntawm thawj lub lens convex raug suav hais tias yog ib yam khoom los ntawm lub lens convex thib ob. Qhov deb ntawm thawj daim duab / khoom los ntawm lub lens convex thib ob (s2) = qhov deb ntawm ob lub lens convex - qhov deb ntawm thawj daim duab los ntawm thawj lub lens convex = 100 cm - 60 cm = 40 cm.
1/s2' = 1/f2 – 1/s2
1/s2'= 1/80 – 1/40 = 1/80 – 2/80 = -1/80
s2' = -80/1 = -80 cm
Daim duab kawg yog 80 cm ntawm lub lens convex thib ob.
Qhov nrug kawg ntawm daim duab yog qhov tsis zoo, txhais tau tias daim duab kawg yog pseudo lossis cuav vim tias daim duab tsis dhau los ntawm lub teeb ci (daim duab kawg yog sab laug ntawm lub lens convex thib ob).
b) Kev ua kom daim duab loj dua
Kev nthuav dav ntawm daim duab los ntawm thawj lub lens convex:
m1 = -s1'/s1 = -60 cm/30 cm = -2 zaug
Lub lens convex ua rau daim duab loj dua 2 npaug ntawm qhov loj ntawm yam khoom.
Qhov kev loj ntawm daim duab nrog lub cim tsis zoo txhais tau tias daim duab tig rov qab.
Kev nthuav dav ntawm daim duab los ntawm lub lens convex thib ob:
m2 = -s2'/s2 = -(-80 cm)/40 cm = 80/40 = 2 zaug
Lub lens convex thib ob ua rau lub khoom loj dua (duab ntawm lub lens convex thawj zaug) los ntawm 2 npaug.
Tag nrho cov duab loj dua yog:
m = (m1)(m2) = (-2)(2) = -4 zaug
Daim duab kawg loj dua 4 npaug ntawm qhov loj ntawm yam khoom lossis qhov siab ntawm daim duab kawg siab dua 4 npaug ntawm qhov siab ntawm yam khoom. Tag nrho qhov loj me yog qhov tsis zoo txhais tau tias daim duab tig rov qab (daim duab kawg tig rov qab yog li daim duab kawg yuav tsum nyob rau sab laug ntawm lub lens convex thib ob).
Cov lus nug txog ob lub lens concave convex
1. Ob lub iav convex uas muaj qhov ntev focal ntawm 40 cm thiab 20 cm raug muab tso ze ua ke qhov twg qhov deb ntawm ob lub iav convex yog 100 cm. Txheeb xyuas qhov deb ntawm daim duab thiab qhov loj ntawm daim duab uas tsim los ntawm ob lub iav convex ntawm ib yam khoom uas yog 120 cm nyob rau pem hauv ntej ntawm thawj lub iav convex!
Cov lus teb tseem ceeb:
(a) qhov deb ntawm daim duab kawg = s2' = 40
(b) tag nrho qhov loj ntawm daim duab = m = 0,5
2. Ib yam khoom nyob deb li ntawm 10 cm rau sab laug ntawm lub lens convex uas muaj qhov ntev focal ntev li ntawm 20 cm. Nyob rau sab xis ntawm lub lens convex yog lub lens convex uas muaj qhov ntev focal ntev li ntawm 50 cm. Yog tias qhov deb ntawm ob lub lens yog 120 cm, txiav txim siab qhov deb ntawm daim duab thiab qhov loj ntawm daim duab uas tsim los ntawm ob lub lens convex!
Cov lus teb tseem ceeb:
(a) qhov deb ntawm daim duab kawg = s2' = 133 cm
(b) tag nrho qhov loj ntawm daim duab = m = -1,7 npaug. Qhov tsis zoo txhais tau tias daim duab tig rov qab.
