$A$ double convex air bubble in water behaves as

The sun subtends an angle of $0.5^{\circ}$ at the earth's surface. Its image is formed by a convex lens of focal length $50 \ \text{cm}$. The diameter of the image will be (in $\text{mm}$)

The distance between an object and a screen is $100\, cm$. $A$ lens can produce a real image of the object on the screen for two different positions between the screen and the object. The distance between these two positions is $40\, cm$. If the power of the lens is close to $\left(\frac{N}{100}\right) D$ where $N$ is an integer,the value of $N$ is.......

$Assertion (A)$: The focal length of a lens does not change when red light is replaced by blue light.
$Reason (R)$: The focal length of a lens does not depend on the colour of the light used.

On which does the convergence capacity of a lens depend?

The graph shows how the magnification $m$ produced by a convex thin lens varies with image distance $v$. What was the focal length of the used lens?