The lamp is at a distance of 30 cm from the collecting lens, and the actual image

The lamp is at a distance of 30 cm from the collecting lens, and the actual image of the lamp is at a distance of 20 cm from the lens. What is the focal length of the lens?

The focal length of a lens can be calculated using the formula:
1 / F = 1 / d + 1 / f, where F is the focal length of the lens (m), d is the distance from the lamp to the lens (d = 30 cm = 0.3 m), f is the distance from the lens to the lamp image ( f = 20 cm = 0.2 m).
Let’s express and calculate the focal length of the lens:
F = (d * f) / (d + f) = (0.3 * 0.2) / (0.3 + 0.2) = 0.12 m.
Answer: The focal length of the lens is 0.12 m.