Yuav kom nkag siab txog daim duab ntawm ib yam khoom uas tsim los ntawm lub lens convex, 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 convex, tom qab ntawd kev tsim cov duab ntawm yam khoom los ntawm lub lens convex , qhov deb ntawm daim duab los ntawm lub lens convex thiab kev loj hlob ntawm daim duab los ntawm lub lens convex tau piav qhia.
Ib lub lens convex (converging lens) muaj qhov ntev focal ntawm 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 cov khoom ntawm lub lens convex me dua qhov ntev ntawm lub lens convex (s < f),
b) qhov deb ntawm cov khoom ntawm lub lens convex yog tib yam li qhov ntev ntawm lub lens convex (s = f),
c) qhov deb ntawm cov khoom ntawm lub lens convex yog loj dua qhov ntev ntawm lub lens convex (s > f).
Kev Sib Tham
Nws yog paub :
Qhov ntev ntawm lub lens concave (f) = 20 cm
Qhov ntev ntawm lub lens convex yog qhov zoo vim tias qhov chaw ntawm lub lens convex yog qhov tseeb lossis dhau los ntawm lub teeb.
Qhov siab ntawm yam khoom (h) = 10 cm
Jawb :
Qhov nrug ntawm cov khoom me dua li qhov ntev ntawm lub lens convex (s > f)
Xav tias qhov deb ntawm yam khoom yog 5 cm, 10 cm thiab 15 cm.
a) 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 = -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 yog loj dua qhov nrug ntawm yam khoom ntawm 5 cm.
Kev loj ntawm daim duab (M)
M = -s'/s = -(-6,7)/5 = 6,7/5 = 1,3
Qhov loj ntawm daim duab loj dua 1, txhais tau tias daim duab raug nthuav dav lossis qhov loj ntawm daim duab loj 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 = (1,3)(10 cm) = 13 cm
Qhov siab ntawm tus duab ntxoov ntxoo yog qhov zoo, txhais tau tias tus duab ntxoov ntxoo sawv ntsug.
b) 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 = -1/20
s' = -20/1 = -20 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 20 cm yog loj dua qhov nrug ntawm yam khoom ntawm 10 cm.
Kev loj ntawm daim duab (M)
M = -s'/s = -(-20)/10 = 20/10 = 2
Qhov loj ntawm daim duab loj dua 1, txhais tau tias daim duab raug nthuav dav lossis qhov loj ntawm daim duab loj 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 = (2)(10 cm) = 20 cm
Qhov siab ntawm tus duab ntxoov ntxoo yog qhov zoo, txhais tau tias tus duab ntxoov ntxoo sawv ntsug.
c) 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 = -1/60
s' = -60/1 = -60 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 60 cm yog loj dua qhov nrug ntawm yam khoom ntawm 15 cm.
Kev loj ntawm daim duab (M)
M = -s'/s = -(-60)/15 = 60/15 = 4
Qhov loj ntawm daim duab loj dua 1, txhais tau tias daim duab raug nthuav dav lossis qhov loj ntawm daim duab loj 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 = (4)(10 cm) = 40 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 convex (s = f)
Tus duab ntxoov ntxoo nyob ntawm qhov deb tsis kawg.
Qhov nrug ntawm cov khoom loj dua qhov ntev ntawm lub lens convex (s > f)
Xav tias qhov deb ntawm yam khoom yog 30 cm, 40 cm thiab 50 cm.
a) 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 = 1/60
s' = 60/1 = 60 cm
Qhov nrug ntawm daim duab zoo txhais tau tias yog daim duab tiag tiag, qhov twg lub teeb ci hla dhau daim duab.
Qhov nrug ntawm daim duab ntawm 60 cm yog loj dua qhov nrug ntawm yam khoom ntawm 30 cm.
Kev loj ntawm daim duab (M)
M = -s'/s = -60/30 = -2
Qhov loj ntawm daim duab loj dua 1, txhais tau tias daim duab raug nthuav dav lossis qhov loj ntawm daim duab loj 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 = (-2)(10 cm) = -20 cm
Qhov siab ntawm tus duab ntxoov ntxoo yog negative, txhais tau tias tus duab ntxoov ntxoo tig rov qab.
b) 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 = 1/40
s' = 40/1 = 40 cm
Qhov nrug ntawm daim duab zoo txhais tau tias yog daim duab tiag tiag, qhov twg lub teeb ci hla dhau daim duab.
Qhov nrug ntawm duab ntxoov ntxoo ntawm 40 cm yog tib yam li qhov nrug ntawm yam khoom ntawm 40 cm.
Kev loj ntawm daim duab (M)
M = -s'/s = -40/40 = -1
Qhov loj ntawm daim duab yog sib npaug rau 1, txhais tau tias qhov loj ntawm daim duab yog tib yam li qhov loj ntawm cov khoom.
Qhov siab ntawm qhov ntxoov ntxoo (h')
Cov qauv duab ntxoov ntxoo loj:
M = h'/h
h' = M h = (-1)(10 cm) = -10 cm
Qhov siab ntawm tus duab ntxoov ntxoo yog negative, txhais tau tias tus duab ntxoov ntxoo tig rov qab.
b) Yog tias qhov deb ntawm yam khoom (s) = 50 cm
Duab nrug (s')
1/s' = 1/f – 1/s = 1/20 – 1/50 = 5/100 – 2/100 = 3/100
s' = 100/3 = 33,3 cm
Qhov nrug ntawm daim duab zoo txhais tau tias yog daim duab tiag tiag, qhov twg lub teeb ci hla dhau daim duab.
Qhov nrug ntawm daim duab ntawm 33,3 cm me dua qhov nrug ntawm yam khoom ntawm 50 cm.
Kev loj ntawm daim duab (M)
M = -s'/s = -33,3/40 = -0,8
Qhov loj ntawm daim duab tsawg dua 1, txhais tau tias 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 negative, txhais tau tias tus duab ntxoov ntxoo tig rov qab.
