JAMB - Physics (1993 - No. 19)
If the focal length of a camera lens is 20cm, the distance from the film at which the lens must be set to produce a sharp image of an object 100cm away is
17cm
20cm
25cm
100cm
คำอธิบาย
F = \(\frac{uv}{u + v}\)
20 = \(\frac{100 \times v}{100 + v}\)
v = 25cm
20 = \(\frac{100 \times v}{100 + v}\)
v = 25cm