A concave mirror has focal length 10 cm. John is looking at a screen placed 15 cm from the mirror, while Ravi is looking into the mirror standing beside John. Both are waiting to see an image, while Rahul is holding a pen 100 cm away from the mirror and bringing it close to the mirror along the principal axis. (a) how far from the mirror will the pen be, when John will see the image? (b) how far from the mirror will the pen be, when Ravi will see the image? (c) who will see an enlarged and erect image of the pen?
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Answer:(a) the image will be 30 cm far from the mirror
(b) any value less than 10 cm
(c) Ravi
Explanation:
(a) focal length is given to be 10 cm and the screen is placed 15 cm from the mirror therefore v is 15 cm. Use mirror formula and calculate u to be 30 cm
(b) this cannot be calculated as u and v are not given therefore any value less than 10 cm would suffice
(c) Ravi obviously because that's the only case of image being virtual and erect
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