In a concave lens, a ray of light emanating from the object parallel to the principal axis of the lens, after refraction: ____.

For a thin concave (diverging) lens, the focal length f is negative, indicating that the focal point lies on the same side as the incoming light (the object side). This point is called the first principal focus (F₁).

Consider a ray that leaves the object and travels parallel to the principal axis toward the lens. When it reaches the lens surface, the refraction law for a diverging lens causes the ray to bend away from the optical axis.

Because the lens has a negative focal length, the emerging ray does not converge to a point on the opposite side of the lens. Instead, if we extend the refracted ray backward (i.e., trace it behind the lens), it appears to originate from the first principal focus F₁.

Thus, after refraction, the ray appears to diverge from the first principal focus. This behavior is characteristic of all rays that are initially parallel to the principal axis when they encounter a concave lens.