Concave and Convex Lenses Ray Diagrams

Types of Lenses

• Bi-convex lenses have two convex surfaces.
• Plano-convex lenses have one convex surface and one plane surface.
• Bi-concave lenses have two concave surfaces.
• Plano-concave lenses have one concave surface and one plane surface.

Convex Lenses

• A convex lens has two surfaces that can be considered as parts of two imaginary spherical surfaces.
• The line that joins the centers of the spheres forming the surfaces is called the principal axis of the lens.
• The principal axis is perpendicular to the surfaces at the points where it intersects with the lens.
• A light ray that enters the lens along the principal axis will leave the lens without bending.
• The mid-point between the two surfaces of the lens is called the optical center of the lens.
• The position and size of the image formed by a convex lens depend on the object distance.
• When the object distance is less than the focal length, the image is virtual, upright, and larger than the object.
• When the object distance is greater than the focal length, the image is real, inverted, and smaller than the object.

Concave Lenses

• A concave lens has two surfaces that can be considered as parts of two imaginary spherical surfaces.
• The line that joins the centers of the spheres forming the surfaces is called the principal axis of the lens.
• A light ray that travels through the principal axis passes through the lens without bending.

Hand Lens or Simple Microscope

• A convex lens makes an object look bigger when the object is placed in front of the lens at a distance less than the focal length.
• A convex lens fitted with a handle is called a hand lens or a simple microscope.
• Hand lenses are commonly used for viewing magnified images of objects such as small insects and parts of flowers.

Microscopes

• A complex microscope is used to observe tiny objects that are not visible to the naked eye.
• It has two lenses called objective and eye piece.
• The combination of lenses produces a very high magnification.

Explore the formation of images by concave and convex lenses and the use of convex lenses to create magnified images. Understand the ray diagrams for hand lenses or simple microscopes.