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UNDERSTANDINGLENSES

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UNDERSTANDINGLENSES

FOCAL POINT &

FOCAL LENGTH

FOR A LENS

IMAGE FORM BY LENSES

POWER LENS

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Types of lenses

Convex lenses Concave lenses

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FOCAL POINT &

 FOCAL LENGTH

  Focal Point: 

Point on th !"inci!al a#i$ %h" all "a$ a" clo$

an' !a"alll to th a#i$ that con(") to it a*t"

!a$$in) th"o+)h a con(# ln$, o" a!!a" to'i(") *"o- it a*t" !a$$in) th"o+)h a conca(

ln$.

  Focal Ln)th: Th 'i$tanc /t%n th *ocal !oint an' th

o!tical cnt".

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Po%" O* Ln$

 Th +nit i$ -a$+"' in Dio!t", D

 Po%" o* th con(# ln$ i$ !o$iti(,

 an' !o%" *o" conca( ln$ i$ n)ati(.

Po%" O* Ln$ 0 1

* 

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E2AMPLE

  Th *oc+$ ln)th o* a conca( ln$

i$ )i(n a$ 34c-. What i$ th

!o%" o* th ln$5

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MAGNIFICATION

 Th $i-!l$t %a to co-!a" th

i-a) %ith o/6ct i$ / "atio o* th $i7.

Thi$ "atio i$ th lina" -a)ni*ication.

Lina" -a)ni*ication,- 0 Si7 o* i-a)

  Si7 o* o/6ct

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 Th "atio o* i-a) $i7 to o/6ct $i7 i$

th $a- a$ th "atio o* i-a) 'i$tanc

to o/6ct 'i$tanc.

Si7 o* i-a) 0 I-a) 'i$tanc 8(9

 Si7 o* o/6ct O/6ct 'i$tanc 8+9

- 0 h1 0 (

  ho  +

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E2AMPLE

Fi)+" $ho%$ th !o$ition o* an i-a), I o* an o/6ct, O *o"-' / con(# ln$.

Th hi)ht o* th o/6ct, O i$ c-. I* OL

0 3;c- an' OI 0

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LENS FORMULA (con(# ln$9 

 * = *ocal ln)th,+ = o/6ct 'i$tanc,

( = i-a) 'i$tanc,

1 > 1 0 1

+ ( * 

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Sign Positive value(+ )

NegativeValue (-)

u Real Virtual

v Real Virtual

f Convex lense Concave lense

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E2AMPLE

  An o/6ct i$ !lac' in *"ont o* a con(#

ln$ %ith *ocal ln)th o* 1;c-. Fin' th

i-a) !o$ition, an' -a)ni*ication o*

th i-a) *o"-' %hn th o/6ct

'i$tanc i$ 1c-.

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UNDERSTANDING

LENSES

MAGNIFICATION

LENS FORMULA

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• DO PRACTICE .?, @UESTIONS 1=?ON PAGE 14 FROM YOUR TE2T

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