Two similar plano-convex lenses are combined | vedclass

Name: Exam Paper Generator | JEE NEET Paper Generator | Vedclass
Brand: Vedclass
Rating: 5 (35 reviews)

Question

(B) When two thin lenses with focal lengths $f_1$ and $f_2$ are placed in contact,the equivalent focal length $F$ is given by $\frac{1}{F} = \frac{1}{

Vedclass · Accepted Answer

$1:1:1$

Vedclass · Answer

(B) When two thin lenses with focal lengths $f_1$ and $f_2$ are placed in contact,the equivalent focal length $F$ is given by $\frac{1}{F} = \frac{1}{f_1} + \frac{1}{f_2}$.In each of the three cases shown,we are combining two identical plano-convex lenses,each having a focal length $f$. For case $1$: The lenses are combined to form a biconvex lens. The power is $P = P_1 + P_2 = \frac{1}{f} + \frac{1}{f} = \frac{2}{f}$,so $F_1 = \frac{f}{2}$.For case $2$: The lenses are combined such that their curved surfaces face the same direction. The power is $P = P_1 + P_2 = \frac{1}{f} + \frac{1}{f} = \frac{2}{f}$,so $F_2 = \frac{f}{2}$.For case $3$: The lenses are combined such that their curved surfaces face each other. The power is $P = P_1 + P_2 = \frac{1}{f} + \frac{1}{f} = \frac{2}{f}$,so $F_3 = \frac{f}{2}$.Since $F_1 = F_2 = F_3$,the ratio of the focal lengths is $1:1:1$.

Two similar plano-convex lenses are combined together in three different ways as shown in the figure. The ratio of the focal lengths in the three cases will be

Similar Questions

Let $x+y=k$ be a normal to the parabola $y^2=12x$. If $p$ is the length of the perpendicular from the focus of the parabola onto this normal,then $4k-2p^2$ is equal to

In the circuit shown in the figure, what is the value of $I_1$ just after pressing the key $K$?

The radius of gyration of a disc of mass $50\,g$ and radius $2.5\,cm$,about an axis passing through its centre of gravity and perpendicular to the plane,is ....... $cm$.

Crystalline sodium chloride is an insulator of electricity because $......$

Which one of the following gives a sooty flame on combustion?

Vedclass Test Series

Exam Paper Generator

Online Exam Module