You visited us 4 times! Enjoying our articles? Unlock Full Access!

Byju's Answer

Standard XII

Physics

Lens Maker's Formula

Three lenses ...

Question

Three lenses L1, L2, L3 are placed co-axially as shown in figure. Focal length's of lenses are given 30 cm, 10 cm and 5 cm respectively. If a parallel beam of light falling on lens $L_{1}$ , emerging $L_{3}$ as a convergent beam such that it converges at the focus of $L_{3}$ . Distance between $L_{1}$ and $L_{2}$ will be

40 cm

No worries! We‘ve got your back. Try BYJU‘S free classes today!

30 cm

No worries! We‘ve got your back. Try BYJU‘S free classes today!

20 cm

Right on! Give the BNAT exam to get a 100% scholarship for BYJUS courses

10 cm

No worries! We‘ve got your back. Try BYJU‘S free classes today!

Open in App

Solution

The correct option is C 20 cm
According to the problem, combination of $L_{1}$ and $L_{2}$ act a simple glass plate. Hence according to formula
$\frac{1}{F} = \frac{1}{f_{1}} + \frac{1}{f_{2}} - \frac{d}{f_{1} f_{2}}$
$\frac{1}{f_{1}} + \frac{1}{f_{2}} - \frac{d}{f_{1} f_{2}} = 0 \Rightarrow \frac{1}{f_{1}} + \frac{1}{f_{2}} = \frac{d}{f_{1} f_{2}}$
$\Rightarrow \frac{1}{30} - \frac{1}{10} = \frac{d}{30 \times - 10} \Rightarrow \frac{- 20}{30 \times 10} = - \frac{d}{30 \times 10}$
$\Rightarrow d = 20 c m$

Suggest Corrections

Similar questions

Q. Three lenses

L_{1}, L_{2}, L_{3}

are placed co-axially as shown in figure. Focal length's of lenses are given 30 cm, 10 cm and 5 cm respectively. If a parallel beam of light falling on lens

L_{1}

, emerging

L_{3}

as a convergent beam such that it converges at the focus of

l_{3}

. Distance between

L_{1} a n d L_{2}

will be :

Q. You are given three lens

L_{1}, L_{2}

and

L_{3}

each of focal length

10 c m

. An object is kept at

15 c m

in front of

L_{1}

, as shown. The final real image is formed at the focus

^{'} I^{'}

L_{3}

. Find the separations between

L_{1}, L_{2}

and

L_{3}

3 lenses L1, L2 and L3 each of focal length 30 cm are placed coaxially .an object is held at 60cm from the optical centre of lens L1.the final image is formed at the focus os L3.Calculate the separation between 1) L1 and L2 2) L2 and L3

Q. Consider three converging lenses

L_{1}, L_{2}

and

L_{3}

having identical geometrical construction. The refractive indices of

L_{1}

and

L_{2}

are

μ_{1}

and

μ_{2}

respectively. The upper half of the lens

L_{3}

has refractive index

μ_{1}

and the lower half has

μ_{2}

as shown in the figure. A point object O has an image at

O_{1}

by the lens

L_{1}

and at

O_{2}

by the lens

L_{2}

placed in the same position. If

L_{3}

is placed at the same place:

Q. Consider three converging lenses

L_{1}

L_{2}

and

L_{3}

having identical geometrical construction. The refractive index of

L_{1}

and

L_{2}

are

μ_{1}

and

μ_{2}

respectively. The upper half of the lens

L_{3}

has a refractive index

μ_{1}

and the lower half has

μ_{2}

. A point O is imaged at

O_{1}

by the lens

L_{1}

and at

O_{2}

by the lens

L_{2}

placed in same position. If

L_{3}

is placed at same place,

Join BYJU'S Learning Program

Three lenses L1, L2, L3 are placed co-axially as shown in figure. Focal length's of lenses are given 30 cm, 10 cm and 5 cm respectively. If a parallel beam of light falling on lens L1, emerging L3 as a convergent beam such that it converges at the focus of L3. Distance between L1 and L2 will be

The correct option is C 20 cmAccording to the problem, combination of L1 and L2 act a simple glass plate. Hence according to formula 1F=1f1+1f2−df1f2 1f1+1f2−df1f2=0⇒1f1+1f2=df1f2 ⇒130−110=d30×−10⇒−2030×10=−d30×10 ⇒d=20 cm