Yuav kom nkag siab txog daim duab ntawm ib yam khoom uas tsim los ntawm lub lens concave, tshuaj xyuas cov lus nug thiab kev sib tham hauv qab no. Hauv cov lus nug no, nws xav tias yam khoom nyob ntawm qhov deb ntawm lub lens concave, tom qab ntawd qhov kev tsim ntawm yam khoom daim duab los ntawm lub lens concave , qhov deb ntawm daim duab los ntawm lub lens concave thiab qhov kev loj hlob ntawm daim duab los ntawm lub lens concave tau piav qhia.
Qhov ntev ntawm lub lens concave (lub lens diverging) yog 20 cm. Ib yam khoom 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 cov khoom loj dua qhov ntev ntawm lub lens concave,
Kev Sib Tham
Nws yog paub :
Qhov ntev ntawm lub lens concave (f) = -20 cm
Qhov ntev ntawm lub lens concave yog qhov tsis zoo vim tias qhov chaw ntawm lub lens concave yog virtual lossis tsis dhau los ntawm lub teeb beam.
Qhov siab ntawm yam khoom (h) = 10 cm
Jawb :
Qhov nrug ntawm cov khoom me dua qhov ntev ntawm lub lens concave (s > f)
Xav tias qhov deb ntawm yam khoom yog 5 cm, 10 cm thiab 15 cm.
a) Qhov ntev ntawm lub zeem muag -20 cm thiab yog tias qhov deb ntawm yam khoom (s) = 5 cm
Duab nrug (s')
1/s' = 1/f – 1/s = -1/20 – 1/5 = -1/20 – 4/20 = -5/20
s' = -20/5 = -4 cm
Qhov deb ntawm daim duab tsis zoo txhais tau tias yog daim duab virtual, qhov twg lub teeb tsis hla dhau daim duab.
Qhov nrug ntawm daim duab ntawm 4 cm me dua qhov nrug ntawm yam khoom ntawm 5 cm.
Kev loj ntawm daim duab (M)
M = -s'/s = -(-4)/5 = 4/5 = 0,8
Qhov loj ntawm daim duab tsawg dua 1, txhais tau tias daim duab raug txo lossis qhov loj ntawm daim duab me dua qhov loj ntawm yam khoom.
Qhov siab ntawm qhov ntxoov ntxoo (h')
Cov qauv duab ntxoov ntxoo loj:
M = h'/h
h' = M h = (0,8)(10 cm) = 8 cm
Qhov siab ntawm tus duab ntxoov ntxoo yog qhov zoo, txhais tau tias tus duab ntxoov ntxoo sawv ntsug.
b) Qhov ntev ntawm lub zeem muag -20 cm thiab yog tias qhov deb ntawm yam khoom (s) = 10 cm
Duab nrug (s')
1/s' = 1/f – 1/s = -1/20 – 1/10 = -1/20 – 2/20 = -3/20
s' = -20/3 = -6,7 cm
Qhov deb ntawm daim duab tsis zoo txhais tau tias yog daim duab virtual, qhov twg lub teeb tsis hla dhau daim duab.
Qhov nrug ntawm daim duab ntawm 6,7 cm me dua qhov nrug ntawm yam khoom ntawm 10 cm.
Kev loj ntawm daim duab (M)
M = -s'/s = -(-6,7)/10 = 6,7/10 = 0,67
Qhov loj ntawm daim duab tsawg dua 1, txhais tau tias daim duab raug txo lossis qhov loj ntawm daim duab me dua qhov loj ntawm yam khoom.
Qhov siab ntawm qhov ntxoov ntxoo (h')
Cov qauv duab ntxoov ntxoo loj:
M = h'/h
h' = M h = (0,67)(10 cm) = 6,7 cm
Qhov siab ntawm tus duab ntxoov ntxoo yog qhov zoo, txhais tau tias tus duab ntxoov ntxoo sawv ntsug.
c) Qhov ntev ntawm lub zeem muag -20 cm thiab yog tias qhov deb ntawm yam khoom (s) = 15 cm
Duab nrug (s')
1/s' = 1/f – 1/s = -1/20 – 1/15 = -3/60 – 4/60 = -7/60
s' = -60/7 = -8,6 cm
Qhov deb ntawm daim duab tsis zoo txhais tau tias yog daim duab virtual, qhov twg lub teeb tsis hla dhau daim duab.
Qhov nrug ntawm daim duab ntawm 8,7 cm me dua qhov nrug ntawm yam khoom ntawm 15 cm.
Kev loj ntawm daim duab (M)
M = -s'/s = -(-8,6)/10 = 8,6/10 = 0,86
Qhov loj ntawm daim duab tsawg dua 1, txhais tau tias daim duab raug txo lossis qhov loj ntawm daim duab me dua qhov loj ntawm yam khoom.
Qhov siab ntawm qhov ntxoov ntxoo (h')
Cov qauv duab ntxoov ntxoo loj:
M = h'/h
h' = M h = (0,86)(10 cm) = 8,6 cm
Qhov siab ntawm tus duab ntxoov ntxoo yog qhov zoo, txhais tau tias tus duab ntxoov ntxoo sawv ntsug.
Qhov nrug ntawm cov khoom yog tib yam li qhov ntev ntawm lub lens concave (s = f)
Qhov ntev ntawm lub zeem muag (f) = qhov nrug ntawm yam khoom (s) = 20 cm.
Duab nrug (s')
1/s' = 1/f – 1/s = -1/20 – 1/20 = -2/20 = -2/20
s' = -20/2 = -10 cm
Qhov deb ntawm daim duab tsis zoo txhais tau tias yog daim duab virtual, qhov twg lub teeb tsis hla dhau qhov ntxoov ntxoo.
Qhov nrug ntawm daim duab ntawm 10 cm me dua qhov nrug ntawm yam khoom ntawm 20 cm.
Kev loj ntawm daim duab (M)
M = -s'/s = -(-10)/20 = 10/20 = 0,5
Qhov loj ntawm daim duab tsawg dua 1, txhais tau tias daim duab raug txo lossis qhov loj ntawm daim duab me dua qhov loj ntawm yam khoom.
Qhov siab ntawm qhov ntxoov ntxoo (h')
Cov qauv duab ntxoov ntxoo loj:
M = h'/h
h' = M h = (0,5)(10 cm) = 5 cm
Qhov siab ntawm tus duab ntxoov ntxoo yog qhov zoo, txhais tau tias tus duab ntxoov ntxoo sawv ntsug.
Qhov nrug ntawm cov khoom loj dua qhov ntev ntawm lub lens concave (s > f)
Xav tias qhov deb ntawm cov khoom yog 30 cm thiab 40 cm.
a) Qhov ntev ntawm lub zeem muag -20 cm thiab yog tias qhov deb ntawm yam khoom (s) = 30 cm
Duab nrug (s')
1/s' = 1/f – 1/s = -1/20 – 1/30 = -3/60 – 2/60 = -5/60
s' = -60/5 = -12 cm
Qhov deb ntawm daim duab tsis zoo txhais tau tias yog daim duab virtual, qhov twg lub teeb tsis hla dhau daim duab.
Qhov nrug ntawm daim duab ntawm 12 cm me dua qhov nrug ntawm yam khoom ntawm 30 cm.
Kev loj ntawm daim duab (M)
M = -s'/s = -(-12)/30 = 12/30 = 0,4
Qhov loj ntawm daim duab tsawg dua 1, txhais tau tias daim duab raug txo lossis qhov loj ntawm daim duab me dua qhov loj ntawm yam khoom.
Qhov siab ntawm qhov ntxoov ntxoo (h')
Cov qauv duab ntxoov ntxoo loj:
M = h'/h
h' = M h = (0,4)(10 cm) = 4 cm
Qhov siab ntawm tus duab ntxoov ntxoo yog qhov zoo, txhais tau tias tus duab ntxoov ntxoo sawv ntsug.
b) Qhov ntev ntawm lub zeem muag -20 cm thiab yog tias qhov deb ntawm yam khoom (s) = 40 cm
Duab nrug (s')
1/s' = 1/f – 1/s = -1/20 – 1/40 = -2/40 – 1/40 = -3/40
s' = -40/3 = -13 cm
Qhov deb ntawm daim duab tsis zoo txhais tau tias yog daim duab virtual, qhov twg lub teeb tsis hla dhau daim duab.
Qhov nrug ntawm daim duab ntawm 13 cm me dua qhov nrug ntawm yam khoom ntawm 40 cm.
Kev loj ntawm daim duab (M)
M = -s'/s = -(-13)/40 = 13/40 = 0,3
Qhov loj ntawm daim duab tsawg dua 1, txhais tau tias daim duab raug txo lossis qhov loj ntawm daim duab me dua qhov loj ntawm yam khoom.
Qhov siab ntawm qhov ntxoov ntxoo (h')
Cov qauv duab ntxoov ntxoo loj:
M = h'/h
h' = M h = (0,3)(10 cm) = 3 cm
Qhov siab ntawm tus duab ntxoov ntxoo yog qhov zoo, txhais tau tias tus duab ntxoov ntxoo sawv ntsug.
