Lens Makers Formula/ Len's Formula

Practice Questions:

Question 1: difficult

As shown in figure, a convergent lens is placed inside a cell filled with liquid. The lens has focal length +20 cm when in air, and its material has refractive index 1.50. If the liguid has refractive index 1.60, the focal length of the system is :

1. +80 cm

2. -80 cm

3. -24 cm

4. -100 cm

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Question 2: difficult

Two convex lens each of focal length 20 cm are separated by 125 cm. An object of height 0.5 cm placed at distance 25 cm left side from the first lens then, find height of the final image.

1. 4 cm

2. 2 cm

3. 0.5 cm

4. 8 cm

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Question 3: difficult

A thin equiconvex glass lens of focal length 10 cm is cut and separated and a material of refractive index 3 is filled between them. What is the focal length of the combination ?
\[\left( \mu_{glass}=1.5\right)\]

1. –10cm

2. –10/4 cm

3. –10/3 cm

4. None of these

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Question 4: difficult

Match the correct u-v graph with optical system using Cartesian sign conventions :

1. a – p, b – s, c – r, d – q

2. a – p, b – r, c – s, d – q

3. a – s, b – r, c – q, d – p

4. a – p, b – s, c – q, d – r

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