In the displacement method,the distance between the object and the screen is $70 \, cm$. The focal length of the lens is $16 \, cm$. The distance between the positions of the lens for the magnified and diminished images will be ..... $cm$.

$A$ convex lens forms a real image of a point object placed on its principal axis. If the upper half of the lens is painted black,the image will

$A$ converging lens of focal length $20\, cm$ and diameter $5\, cm$ is cut along the line $AB$. The part of the lens shown shaded in the diagram is now used to form an image of a point $P$ placed $30\, cm$ away from it on the line $XY$,which is perpendicular to the plane of the lens. The image of $P$ will be formed:

$A$ lens placed $10 \,cm$ away from a wall casts a sharp inverted image of a candle on it. It again casts a sharp image when the lens is moved $20 \,cm$ further away from the wall. Now,the candle and the lens are moved such that a sharp inverted image with unit magnification is formed on the wall. To achieve this configuration,the candle was moved

$A$ thin equiconvex lens is made of glass of refractive index $1.5$ and its focal length is $0.2 \ m$. If it acts as a concave lens of $0.5 \ m$ focal length when dipped in a liquid,the refractive index of the liquid is:

Write the equation and definition of lateral magnification for a lens.