The correct option is **B. Concave lens**. ### Detailed Explanation: 1. **Understanding Lens Types**: - **Convex Lens**: A convex lens is thicker at the center than at the edges. It converges parallel rays of light to a focal point. This type of lens is used in magnifying glasses and cameras. - **Concave Lens**: A concave lens is thinner at the center than at the edges. It diverges parallel rays of light, making them spread out as if they are coming from a focal point behind the lens. This type of lens is commonly used in glasses for nearsightedness (myopia). - **Biconvex Lens**: A biconvex lens is a type of convex lens that is curved outward on both sides. It also converges light rays. - **Cylindrical Lens**: A cylindrical lens has a curvature in one direction only. It can focus light into a line rather than a point and is used in applications like correcting astigmatism. 2. **Why the Concave Lens Diverges Light**: - When parallel rays of light enter a concave lens, they strike the lens at different angles. The lens's shape causes the rays to bend outward (diverge) rather than converge. - The bending occurs due to the lens's refractive properties, which are governed by Snell's Law. As light passes from air (a less dense medium) into the glass of the lens (a denser medium), it slows down and bends towards the normal line (an imaginary line perpendicular to the surface at the point of incidence). However, because the lens is thinner in the center, the rays diverge after passing through the lens. 3. **Why Other Options Are Incorrect**: - **A. Convex Lens**: This option is incorrect because a convex lens is thicker at the center and converges light rays, not diverges them. - **C. Biconvex Lens**: This option is also incorrect for the same reason as the convex lens. A biconvex lens converges light rays and is not thinner at the center. - **D. Cylindrical Lens**: While a cylindrical lens can diverge light, it does so in only one direction and is not defined by being thinner at the center than at the edges. It is primarily used for correcting astigmatism, not for general light divergence. ### Formulas and Concepts: - **Lens Maker's Formula**: This formula relates the focal length (f) of a lens to the radii of curvature (R1 and R2) of its surfaces and the refractive index (n) of the lens material: \[ \frac{1}{f} = (n - 1) \left( \frac{1}{R_1} - \frac{1}{R_2} \right) \] For a concave lens, the focal length is considered negative, indicating that it diverges light. ### Common Pitfalls: - Confusing the types of lenses based on their shapes and effects on light. Remember that the curvature and thickness at the center are key indicators of whether a lens is concave or convex. - Misunderstanding the direction of light rays after passing through different types of lenses. Always visualize or draw the path of light rays to clarify their behavior. ### Revision Summary: - A **concave lens** is thinner at the center and diverges light rays. - It is used in applications like glasses for nearsightedness. - A **convex lens** converges light and is thicker at the center. - Understanding the properties of lenses is crucial for solving optics problems in physics.