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Wave Optics

Question
CBSEENPH12039832
Wired Faculty App

A rod of length  10 cm lies along the principal axis of a concave mirror of focal length 10 cm in such way that it end closer to pole is 20  cm away from the mirror. The length of the image is

  • 10 cm

  • 15 cm

  • 2.5 cm

  • 5 cm

Solution

D.

5 cm

 By mirror formula, image distance of A 
1 over straight v plus 1 over straight u space equals 1 over straight f

fraction numerator 1 over denominator straight v subscript straight A space end fraction space plus 1 over straight u space equals 1 over straight f 1 over straight v subscript straight A plus fraction numerator 1 over denominator left parenthesis negative 30 right parenthesis end fraction space equals space fraction numerator 1 over denominator negative 10 end fraction space straight v subscript straight A space equals negative 15 space cm Also comma space image space distance space of space straight C straight v subscript straight c space equals negative 20 space cm The space length space of space image space equals space vertical line straight V subscript straight A minus space straight V subscript straight c vertical line equals space vertical line minus 15 minus left parenthesis negative 20 right parenthesis vertical line equals space 5 space cm

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