$A$ concave mirror gives an image three times as large as the object placed at a distance of $20 \ cm$ from it. For the image to be real,the focal length should be ...... $cm$.
- A$-10$
- B$-15$
- C$-20$
- D$-30$
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Match the following columns:
Column-$I$ Column-$II$ $(A)$ Linnaeus $(i)$ First to discover viruses $(B)$ Ivanowsky $(ii)$ First to discover lichens $(C)$ Iyengar $(iii)$ Father of Indian Bryology $(D)$ Tulasne $(iv)$ Father of Taxonomy $(E)$ Shiv Ram Kashyap $(v)$ Father of modern Phycology in India
| Column-$I$ | Column-$II$ |
|---|---|
| $(A)$ Linnaeus | $(i)$ First to discover viruses |
| $(B)$ Ivanowsky | $(ii)$ First to discover lichens |
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