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Standard X

Physics

Image Formation by Spherical Lenses

You are given...

Question

You are given three lens $L_{1}, L_{2}, L_{3}$ each of focal length $15 c m$ . An object is kept at $20 c m$ in front of $L_{1}$ , as shown. The final real image is formed at the focus $^{'} I^{'}$ of $L_{3}$ . Find the separations between $L_{1}, L_{2}$ and $L_{3}$ .

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Solution

The separations between the lenses will be as follows,

Distance between L2 and L3 doesn’t matter as the image formed by L2 is at infinity so that X2 can take any value.
Image by L3 is formed at the focus. So the object should lie at infinity for L3.
So, L2 will form image at infinity and the object for L2 should be at its focus.
But wehave seen above that the image by L1 is formed at $20 c m$ right of L1 which is at $20 c m$ left of L2.
So, Distance between $L 1 + L 2 = 15 + 20 = 35 c m$

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You are given three lens L1,L2,L3 each of focal length 15cm. An object is kept at 20cm in front of L1, as shown. The final real image is formed at the focus ′I′ of L3. Find the separations between L1,L2 and L3.

You are given three lens $L_{1}, L_{2}, L_{3}$ each of focal length $15 c m$ . An object is kept at $20 c m$ in front of $L_{1}$ , as shown. The final real image is formed at the focus $^{'} I^{'}$ of $L_{3}$ . Find the separations between $L_{1}, L_{2}$ and $L_{3}$ .