1. Magnification: The primary function of a magnifier is to enlarge the size of an object or text to make it easier to see. This magnification is achieved by bending light rays with the convex lens. As light passes through the lens, it refracts or bends inward, converging the light rays to a focal point.

2. Focal Length: The focal length is the distance between the lens and its focal point. In magnifiers, the focal length is relatively short, usually a few inches or centimeters. The shorter the focal length, the greater the magnification achieved.

3. Near Point: The near point is the closest distance at which the eye can focus on an object. As we age, the near point tends to increase, making it harder to focus on close-up objects. Magnifiers allow individuals to bring the object within the near point distance, enabling clear and magnified viewing.

4. Virtual Image: When an object is placed closer to a convex lens than its focal length, a virtual image is formed on the opposite side of the lens. This virtual image appears larger and appears to be farther away from the lens than the actual object.

5. Angular Magnification: The angular magnification of a magnifier is the ratio of the angle subtended by the virtual image when viewed through the magnifier to the angle subtended by the object when viewed without the magnifier. This ratio determines the relative increase in size that the magnifier provides.