Myopia can be corrected with the help of a/an ...

When the power of the eye lens increases,a defect of vision is produced. This defect is known as:

$A$ man suffering from myopia can read a book placed at $10 \ cm$ distance. For reading the book at a distance of $60 \ cm$ with relaxed vision,the focal length of the lens required will be ...... $cm$.

$A$ man can see clearly up to $3 \, m$. Prescribe a lens for his spectacles so that he can see clearly up to $12 \, m$.

$A$ student studying the similarities and differences between a camera and the human eye makes the following observations:
$I$. Both the eye and the camera have convex lenses.
$II$. In order to focus,the eye lens expands or contracts while the camera lens moves forward or backward.
$III$. The camera lens produces upside down real images while the eye lens produces only upright real images.
$IV$. $A$ screen in a camera is equivalent to the retina in the eyes.
$V$. $A$ camera adjusts the amount of light entering in it by adjusting the aperture of the lens. In the eye,the cornea controls the amount of light. Which of the above statements are correct?

$A$ man cannot see clearly the objects beyond a distance of $20 \, cm$ from his eyes. To see distant objects clearly,he must use which kind of lenses and of what focal length?