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# The distance between… calculate the focal length of the lens

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**The distance between an object and its real image in a convex lens is 40cm. if the magnification of the image is 3, calculate the focal length of the lens**

- A.
**6.5cm** - B.
**7.5cm** - C.
**8.5cm** - D.
**15.0cm**

**QUICK ANSWER…**

**D**

**DETAILS…**

**Be careful, this problem, when properly solved, will lead to simultaneous equations.**

**Hence, focal length = 15cm**

**Now for the right answer to the above question:**

**Option A is incorrect.****Option B is incorrect.****C is incorrect.****D is the correct answer.**

**KEY-POINTS…**

**You may please note these/this:**

**The object distance is usually from the lens, and the image distance too is usually from the lens, this implies that the distance between them is calculated by simply subtracting one from the other.****In the calculation above, I introduced 3/3 because I intend to manipulate and make the denominator 60 so that I can easily add up the fraction.**

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**/culled from 2019 JAMB-UTME physics question 16/**