JAMB - Physics (1994 - No. 27)
An object is placed in front of a converging lens of a focal length 20cm. The image is virtual and has a magnification of 2. What is the distance of the object from the lens?
5cm
10cm
30cm
40cm
คำอธิบาย
V = -2u
F = \(\frac{uv}{u + v}\)
20 = \(\frac{uv - 2u}{u - 2u}\)
u = 10cm
F = \(\frac{uv}{u + v}\)
20 = \(\frac{uv - 2u}{u - 2u}\)
u = 10cm