Lesson 18.2: Lenses form images by refracting light

Lesson Focus

Lenses bend light to create images. We'll explore how different lens shapes control this bending, known as refraction, to produce the images we see through cameras, magnifying glasses, and more.

Learning Objectives

• Understand how materials like glass or water bend light in a process called refraction.
• Explain how the shape of convex and concave lenses allows them to control light.
• Recognize how lenses gather and focus light rays to form a clear, corresponding image.
• Experiment with a convex lens to see firsthand how it can focus an image.

Light changes direction, a phenomenon called refraction, when it enters a new medium at an angle.

This happens because one side of the light wave changes speed before the other, causing a turn.

Light bends toward an imaginary line called the normal in denser materials where it slows.

Rainbows appear when sunlight is refracted and reflected by water droplets in the air.

Each spherical drop acts like a tiny prism, using refraction to separate white light into its spectrum of colors.

Because different colors bend at slightly different angles, we see them as separate bands, connecting to how lenses work.

A lens is a clear tool that uses its curved shape to refract light in a specific way.

A convex lens, which curves outward, bends parallel light rays inward to meet at a single point.

In contrast, a concave lens, which curves inward, spreads parallel light rays outward.

A convex lens forms an image by gathering light from an object.

Light rays are refracted as they enter and leave the lens.

All rays from a single point on the object are bent to meet at a corresponding point on the other side, forming a complete, focused image.

The image from a convex lens depends on the object's distance, measured relative to the focal length.

An object more than two focal lengths away creates a smaller, upside-down image (like in a camera).

An object closer than one focal length creates a larger, right-side-up image (like a magnifying glass).

A concave lens always creates a smaller, right-side-up image, no matter the object's distance.

It works by refracting light rays outward, causing them to diverge. Your eye traces these spreading rays back to a point where they seem to originate, forming the reduced image.

Can you think of where this might be useful?