JAMB - Physics (1980 - No. 18)
If the magnification of a virtual image formed of an object 10cm from a convex lens is 3, then the focal length of the lens is
10cm
15cm
16cm
19cm
20cm
คำอธิบาย
V = 3u, U = 10cm
therefore U = -ve,
F = \(\frac{UV}{U + V}\)
= \(\frac{10 \times (-30)}{10 - 30 }\)
= 15cm
therefore U = -ve,
F = \(\frac{UV}{U + V}\)
= \(\frac{10 \times (-30)}{10 - 30 }\)
= 15cm