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(a) What type of lens is used as a magnifying glass?
(b) What type of lens is used to correct the defect of vision called myopia?
(c) A convex lens has a focal length of 10.5 cm. Where should an object be placed in front of this convex lens so as to obtain an image which is real, inverted and same size as the object?
(a) Convex lens is a type of lens which is used as a magnifying glass.
Explanation
When an object is placed at a distance less than the focus i.e., between optical centre, $C$ and focus, $F'$ of a convex lens, then the image formed is virtual, erect, larger than the object (enlarged or magnified), and behind the object (on the left side of the lens).
(b) Concave lens is a type of lens used to correct the defect of vision called myopia.
Image is posted for reference only
(c) When an object is placed at $2F'$ in front of the convex lens, then the image formed is real, inverted, same size as the object, and at $2F$ on the right side of the lens.
Here,
$f$ (focal length) is given 10.5 cm, then the $2f$ will be 21 cm $(2\times {10.5})$.
So, Object distance from the lens = 21 cm (as object is at $2f$)
Thus, the object should be placed at a distance of $2f$ which is 21 cm in front of the lens (on the left side).
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