Question

Rishi went to a palmist to show his palm. The palmist used a special lens
for this purpose.
(1) State the nature of the lens and reason for its use.
(11) Where should the palmist place hold the lens so as to have a real and
magnified image of an object?
(i) If the focal length of this lens is 10 cm, the lens is held at a distance
of 5 cm from the palm, use lens formula to find the position and size
of the image.
​

Answer 1

i) The palmist uses a convex lens in order to resolve the palm-lines magnified.

ii) The position of the palm lies between the principal focus and the second principal focus of the lens.

iii) $i=-10\ cm$ here the negative sign means that the image is formed on the same side as that of the image.

Explanation:

i) The palmist uses the magnifying glass which is a convex lens in order to magnify the palm-lines for a clear visibility.

ii) The palmist must hold the lens close to the palm so that it lies within the principal focus and the second principal focus of the lens and the image hence formed is real, magnified but inverted in orientation.

iii)

GIVEN:

focal length of the lens, $f=10\ cm$

position of the object (palm), $o=5\ cm$

Using the lens formula:

$\frac{1}{f} =\frac{1}{i} +\frac{1}{o}$

where:

$i=$ position of the image

putting the respective values in above equation:

$\frac{1}{10} =\frac{1}{i}+\frac{1}{5}$

$i=-10\ cm$ here the negative sign means that the image is formed on the same side as that of the image.

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TOPIC: magnifying glass

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