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ICSE Class 10 Physics 2023 Solved Paper

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Question : 44
Total: 76
A convex lens of focal length 10‌cm is placed at a distance of 60‌cm from a screen. How far from the lens should an object be placed so as to obtain a real image on the screen?
Solution:  
Given: f=+10‌cm,v=+60‌cm,u= ?
We know,
‌‌
1
f
‌=‌
1
v
−‌
1
u
∴‌‌
1
v
‌=‌
1
f
+‌
1
u
⇒‌‌
1
+60
‌=‌
1
+10
+‌
1
u
⇒‌‌
1
u
‌=‌
1
60
−‌
1
10
=‌
1−6
60
⇒‌‌
1
u
‌=‌
−5
60
‌ or ‌‌u‌=‌
60
−5
=−12‌cm.
Thus, the object must be placed at a distance of 12‌cm in front of the lens.
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