If the distance of the object is 250 cm and the distance of the image is 140 cm, I say that the focal length is 390 cm.
True or false
False.
The focal length can be calculated using the lens equation:
1/f = 1/d_o + 1/d_i
where f is the focal length, d_o is the object distance, and d_i is the image distance.
Plugging in the given values:
1/f = 1/250 + 1/140
Simplifying:
1/f = (140 + 250) / (250 * 140)
1/f = 390/35,000
f = 35,000 / 390
f ≈ 89.74 cm
Therefore, the correct focal length is approximately 89.74 cm, not 390 cm.