Why can a magnifying glass enlarge an object image?
A magnifying glass is a simple optical tool used to read a book, and the small text will be enlarged, looking very clear. A magnifying glass is made by grinding a substance with very good transparency (like glass). It is thick in the middle, thin at the edge, is a convex piece of lens. Its two sides can be both spherical, or one side is spherical, the other is flat.
Place a magnifying glass in the Sun’s direction (lens perpendicular to the ray of light), the light rays passing through the magnifying glass will converge on a point. That point is the focus. If the tip of a match is placed right in the spotlight, the match soon ignites. The distance between the center of the lens and the focus is called the focal length. If an object is placed in the magnifying glass’s focus, due to the convex lens features caustics. An observer can immediately see a magnified virtual image at a place greater than the distance of the object. Thus, the tiny parts that are not visible, through the magnifying effect of the magnifying glass, can be seen more clearly.
The magnification of the magnifying glass referred to in optics is from the “viewing angle” perspective. If a radian is used to represent the viewing angle, its magnitude is equal to the ratio of the mass’s length to the distance from the eye to the object. When the viewing angle is less than 1 ‘(equivalent to that of an object 1 cm long at 34 m from the outer eye). In the event of low ambient lighting, the viewing angle must be increased, even reaching 1 °.
The effect of a magnifying glass is through increasing the viewing angle that achieves the goal of enlarging the object image. According to calculations, magnifying the magnifying glass is equal to the visible distance divided by the distance between the object and the eye. Use a magnifying glass to see the object, to place the subject in focus. The magnifying glass’s focal length is between 1.0 – 10 cm; the visible distance is 25 cm, so degrees magnification of the magnifying glass in the middle 2.5 – 25 times.
The old glasses used by the elderly are also a kind of convex lenses. Everyone knows that the light of an object emitted only through the refractive effect of the lens in the sphere, converging to the retina seen on the sphere’s posterior wall, can be seen clearly. When looking at an object very far away, the eye can be loosened, and the retina can see a clear image. But looking at a nearby object requires adjusting the eye to increase the refractive index of the lens. As the regulatory capacity of the elderly has deteriorated, it is only possible to let light rays focus on the back of the retina of the eye. Placing a convex lens in front of the eye, allowing the focus of light rays to focus once more, can cause the image to fall into the retina, the elderly eye, thus not blurring.