In a laboratory four convex lenses L1, L2, L3 and L4 of focal lengths 2,4,6 and 8 cm, respectively are available. Two of these lenses form a telescope of length 10 cm and magnifying power 4 . The objective and eye lenses are respectively

Question

In a laboratory four convex lenses L1, L2, L3 and L4 of focal lengths 2,4,6 and 8 cm, respectively are available. Two of these lenses form a telescope of length 10 cm and magnifying power 4 . The objective and eye lenses are respectively (A) L2,L3 (B) L1,L4 (C) L1,L2 (D) L4,L1

Tardigrade Admin · Accepted Answer

Length of tube =10 cm fo+f0=10 cm Magnification m=(f0/fe)=4 fo=4 fe Putting in Eq. (i), 5 fe =10 cm or fe =2 cm and fo =8 cm fo =8 cm , fe=2 cm Hence, L4 and L1 will be used.

Q. In a laboratory four convex lenses $L_{1}, L_{2}, L_{3}$ and $L_{4}$ of focal lengths $2, 4, 6$ and $8 c m$ , respectively are available. Two of these lenses form a telescope of length $10 c m$ and magnifying power $4.$ The objective and eye lenses are respectively

$L_{2}, L_{3}$

$L_{1}, L_{4}$

$L_{1}, L_{2}$

$L_{4}, L_{1}$

Length of tube $= 10 c m$
$f_{o} + f_{0} = 10 c m$
Magnification $m = \frac{f _{0}}{f _{e}} = 4$
$f_{o} = 4 f_{e}$
Putting in Eq. (i),
$5 f_{e} = 10 c m$
or $f_{e} = 2 c m$
and $f_{o} = 8 c m$
$f_{o} = 8 c m, f_{e} = 2 c m$
Hence, $L_{4}$ and $L_{1}$ will be used.

Q. In a laboratory four convex lenses L1​,L2​,L3​ and L4​ of focal lengths 2,4,6 and 8cm, respectively are available. Two of these lenses form a telescope of length 10cm and magnifying power 4. The objective and eye lenses are respectively

L2​,L3​

L1​,L4​

L1​,L2​

L4​,L1​