A diverging lens with f = -33.5 cm is placed 14 cm behind converging lens with f = 20cm. where will an object at infinity be focused?

Respuesta :

Answer:

Explanation:

Focal length of diverging lens,

fd= -33.5 cm

focal length of converging lens,

fc = 20 cm

Now let s is object distance and s' is image distance.

Now using lens formula for conversing lens

\frac1{f_c}=\frac1{s}+\frac1{s'}

f

c

1

=

s

1

+

s

1

Putting all values(object is at s=infinity)

Then image distance

\frac1{s'}= \frac1{f_c}- \frac1{s}

s

1

=

f

c

1

s

1

=\frac1{20}- \frac1{\infin}=

20

1

1

s'=20cms

=20cm

Now using lens formula for diversing lens

s''=14-20=-6cm

Using lens formula

\frac{1}{-33.5} = \frac{1}{-6 }+ \frac{1}{s''' }\\s'''=\frac{(6)\times(-33.5)}{(-33.5+6)}\\s'''=\frac{(-201) }{(-27.5) }

−33.5

1

=

−6

1

+

s

′′′

1

s

′′′

=

(−33.5+6)

(6)×(−33.5)

s

′′′

=

(−27.5)

(−201)

image distance for diverging lens

s''' = 7.3 cm (behind the diverging lens)

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