A) 5 cm
B) 10 cm
C) 15 cm
D) 25 cm
Correct Answer: C
Solution :
By using the lens equation, \[\frac{1}{u}+\frac{1}{v}=\frac{1}{f}\] \[\frac{1}{u}+\frac{1}{-4u}=\frac{1}{20}\to \frac{3}{4u}=\frac{1}{20},u=15\,cm\] Take note that a negative sign must be added to the image distance if the image is a virtual image.You need to login to perform this action.
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