If ${I_1}$ and ${I_2}$ are the sizes of the images for the two positions of the lens in the displacement method,then the size of the object is given by:

An object is placed at a distance of $1.50 \, m$ from a screen. $A$ convex lens is placed between them to produce a four times magnified image on the screen. The focal length of the lens is ..... $cm$.

$A$ student measures the focal length of a convex lens by placing an object pin at a distance '$u$' from the lens and measuring the distance '$v$' of the image pin. The graph between '$u$' and '$v$' plotted by the student should look like:

$A$ plane wave passes through a convex lens. The geometrical shape of the wavefront that emerges is

$A$ bi-convex lens made of glass (refractive index $1.5$) is put in a liquid of refractive index $1.7$. Its focal length will

The far point of a nearsighted person is $6.0 \, m$ from her eyes,and she wears contact lenses that enable her to see distant objects clearly. $A$ tree is $18.0 \, m$ away and $2.0 \, m$ high. How high is the image formed by the contact lenses?