Question #43210

This problem tests the rigorous application of Newton's lens equation ($x_1 x_2 = -f^2$) and the concept of apparent shift due to a glass slab.

The core trap lies in the fact that the slab shifts the apparent object across the first focal point.

Initially, the object is outside the focal length, producing a real image.

The slab shifts the apparent object inside the focal length.

Students who blindly apply the magnitude version of Newton's formula ($xx' = f^2$) will calculate the new distance from the focal point ($x = 10 \text{ cm}$), find $x' = 160 \text{ cm}$, and incorrectly assume the image remains real (at $v = 200 \text{ cm}$), leading to a completely wrong shift of $40 \text{ cm}$.

Proper application requires recognizing the sign change in the object coordinate relative to the focal point, which correctly yields a virtual image and a massive shift of $360 \text{ cm}$.