When an object is placed 60 cm from a converging lens, itforms a real image. Whe

Question

When an object is placed 60 cm from a converging lens, itforms a real image. When the object is moved to 40 cm fromthe lens, the image moves 10 cm farther from the lens. Wat is thefocal length of the lens? ahh another problem i dont know how to do >:( When an object is placed 60 cm from a converging lens, itforms a real image. When the object is moved to 40 cm fromthe lens, the image moves 10 cm farther from the lens. Wat is thefocal length of the lens? ahh another problem i dont know how to do >:(

Explanation / Answer

Let f be the focal length of the lens then, 1/v-1/u=1/f for u=-60cm 1/v-1/-60=1/f for u=-40cm v=v+10cm 1/v+10-1/-40=1/f Equating we have as 1/v-1/-60=1/v+10-1/-40 1/v-1/v+10=1/40-1/60 10/v+10-1/v+10=1/120 9/v+10=1/120 9*120=v+10 v=1070cm Substituting this in any of the above equation we haveas, f=56.814cm Hence we get by it.

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