Question

Calculate the distance at which an object should be placed in front of a convex lens of focal length 10cm to obtain an image double its size
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Answer 1

Answer:

☆Original number of boys=5x

☆Original number of girls = 3x

3x∴5x−50/3x+50 = 9/7

35x – 350 = 27x + 450

=> 35x – 27x = 350 + 450

=> 35x – 27x = 350 + 450=> 8x = 800

=> x = 100

♤Number of boys = 5x

= 5 × 100 = 500

♤Number of girls = 3x

=3 × 100 = 300

\huge\mathfrak\purple{Hope it helps!!}Hopeithelps!!

Answer 2

GiveN :-

• An object should be Placed in front of a convex lens of focal length 10cm.
• The Image is obtained .

To FinD :-

• The distance at which the object should be placed to obtain a image of double size.

SolutioN :-

Here let us take the height of the object be x . Then the Height of the image will be 2x.

And the convex lens has the focal length of 10cm . Here we can use the formula of magnification in terms of focal length and object distance .

$\sf:\implies \pink{ Magnification =\dfrac{f}{f+u}}\\\\\sf:\implies m = \dfrac{10cm}{10cm+u}\\\\\sf:\implies \dfrac{2x}{x}=\dfrac{10cm}{10cm+u}\\\\\sf\implies 2 = \dfrac{10cm}{10cm+u} \\\\\sf:\implies 2(10cm + u)= 10cm \\\\\sf:\implies 20cm + u =10cm \\\\\sf:\implies u = 10cm -20cm \\\\\sf:\implies\boxed{\pink{\frak{ Object\ Distance = (-10 \ cm )}}}$

$\underline{\underline{\blue{\textsf{ Hence the object should be placed at \textbf{ 10cm from optical centre }.}}}}$