Understanding Refraction Through a Convex Lens

When a ray of light passes through a convex lens, it bends. This bending is called refraction. The path of a ray of light after passing through a convex lens depends on the direction it was travelling before it hit the lens. There are specific rules for certain rays that help us understand how convex lenses form images.

Ray Through Principal Focus of Convex Lens

Let's consider the specific case described in the question: a ray of light that passes through the principal focus (also known as the focal point, usually denoted by \(F_1\) or \(F\)) located on one side of the convex lens, before hitting the lens.

According to the rules of refraction for a convex lens:

• A ray of light travelling parallel to the principal axis of the lens, after refraction through the lens, passes through the principal focus (\(F_2\) or \(F'\)) on the other side of the lens.
• A ray of light passing through the principal focus (\(F_1\)) on one side of the lens, after refraction through the lens, emerges parallel to the principal axis.
• A ray of light passing through the optical center (O) of the lens goes straight through without any deviation.

The question asks about a ray passing through the principal focus. Based on the rules above, a ray of light passing through the principal focus of a convex lens before striking the lens will be refracted by the lens and emerge travelling parallel to the principal axis.

Analyzing the Options

Let's look at why the other options are not correct for a ray passing through the principal focus:

• Through the principal focus: A ray passing through the principal focus *before* the lens emerges parallel *after* the lens. It doesn't pass through the principal focus *again* after refraction, unless it's a specific setup like a combination of lenses or reflection involved, which isn't the case here.
• Without any deviation: This only happens for a ray of light that passes through the optical center of the convex lens. A ray through the principal focus *does* deviate; it changes direction to become parallel to the principal axis.
• Through the centre of curvature: The center of curvature is related to the spherical surfaces of which the lens is a part. For a lens, the key points are the optical center, principal foci, and the 2F points (which relate to the radii of curvature). A ray through the principal focus does not typically pass through the center of curvature after refraction in the context of standard ray tracing rules for image formation.

Therefore, the correct path for a ray of light passing through the principal focus of a convex lens after refraction is that it will emerge parallel to the principal axis.

Revision Table: Convex Lens Ray Rules

Additional Information on Convex Lenses

A convex lens is also known as a converging lens because it converges parallel rays of light to a single point (the principal focus). They are thicker at the center than at the edges. Convex lenses are used in many optical instruments like magnifying glasses, cameras, telescopes, and microscopes. The position and nature (real or virtual, inverted or erect, magnified or diminished) of the image formed by a convex lens depend on the position of the object relative to the lens's focal length and 2F points.

Understanding these basic ray tracing rules for a convex lens is fundamental to predicting how images are formed and analyzing optical systems.