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Problem
Problem
When the object is at distances
u
1
u_1
u
1
and
u
2
u_2
u
2
from the optical centre of a convex lens, a real and a virtual image of the same magnification are obtained. The focal length of the lens is a.
u
1
−
u
2
2
\frac{u_1 - u_2}{2}
2
u
1
−
u
2
b.
u
1
+
u
2
u_1 + u_2
u
1
+
u
2
c.
u
1
u
2
\sqrt{u_1 u_2}
u
1
u
2
d.
u
1
+
u
2
2
\frac{u_1 + u_2}{2}
2
u
1
+
u
2
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