A convex lens is thicker at the center and thinner at the lower and upper edges. When light rays parallel to its principal axis fall on the surface of the convex lens, then due to its shape and difference in the refractive index of air and the lens, light rays converge at one point, this point is called the principal focus or focal point. The distance between the optical center and the principal focus is called the focal length. Because of their converging property, they are also known as Convergent lenses.
Types of Convex Lens
Convex lenses are broadly divided into the following categories.
It consists of a spherical surface and a flat surface, i.e., it bugles outward from one side, and it has a plane surface on the other side.
They are also known as Double convex lenses. These lenses bulge outward from both sides. They have comparatively shorter focal lengths than the plano-convex lenses of equal radii and diameter.
They are also called meniscus as they are formed by the combination of a concave lens side and a convex lens side that together form a Concavoconvex lens. Its one surface is curved inward and the other is outward. It has two radii, one radius is of the convex lens surface, while the other radius is of the concave lens surface.
Image Formation by Convex Lens
A convex lens can form both real and virtual images, depending upon the position of the object. When the image is formed on the same side as that of the object, it is called a virtual image. When an image is formed on the opposite side as that of the object, it is called a real image. Let us discuss Image Formation by the Convex lens.
Object at Infinity
A real and inverted image of a point size is formed at the focus point (F2) of the convex lens when the object is placed at an infinite distance.
Object at Beyond Center of Curvature
A real and diminished image is formed on the other side of the convex lens, between the center of curvature (2F) and the focal point (F), when the object is placed behind the center of curvature. The center of curvature is also known as 2F as it is twice the distance of the focal length.
Object at Center of Curvature
A real and inverted image of equal size is formed at the center of curvature of the other side of the convex lens when the object is placed in front of the convex lens at the center of curvature.
Object in Between Center of Curvature and Focal Point
A real and inverted image of larger size than that of the object is formed behind the center of curvature of another side of the convex lens when the object is placed in between the center of curvature and the focal point of the convex lens.
Object at Focal point
A real image of much larger size than that of the object is formed at the infinity on the other side of the convex lens when the object is placed in front of the convex lens at its focal point.
Object at the Distance Less than the Focal Length
A virtual and erect image of a size much larger than that of the object is formed on the same side as that of the object when the object is placed at a distance less than the focal length of the convex lens.
Uses of Convex Lenses in Daily Life
1. Human Eye
The most prime example of the Convex lens in daily life is that it helps us see the world clearly with our eyes. When an object emits light rays of visible wavelength (380-700 nanometers) then it enters our eyes through a lens and falls on the light-sensitive membrane called the retina. A real and inverted image is formed on the retina; the nerve impulses attached to the retina sends this data in the form of signals to the brain, which is eventually interpreted by the brain, and we see the objects clearly. It is very important that the image formed on the retina should be of high intensity because only then we can see a clear image of the object. This task is done by the Convex lens present in our eyes. The convex lens converges the light rays at one point on the retina, hence it provides a clear and sharp image of the object.
2. Magnifying Glasses
The most common use of convex lens is that it is used in magnifying glasses. Magnifying glasses trick our eyes by creating the illusion of a bigger image behind the lens. This illusion is actually the virtual image formed by the convex lens. Magnifying glasses converge the light at one point. When the distance between the object and the convex lens is less than the focal length, a magnified image of the object can be observed.
Convex Lens is used in Eyeglasses to correct farsightedness or hyperopia. People suffering from hyperopia can see distant objects clearly, but they have difficulty seeing the nearby objects. In this condition, the ciliary muscles fail to adjust the focal length of the eye lens, hence the image formed is far beyond the retina. The image thus obtained is not focused on the retina, and the person sees a blurry image. This may happen due to the weakening of ciliary muscles because of several reasons. To correct this condition, a Convex lens is used in the eyeglasses that converge the light rays and focus it on the surface of the retina, hence a bright and clear image is obtained.
The type of lens used in cameras can vary according to the type of photography needed. The lens used in cameras is typically Convex. Convex lens present in cameras can control both the intensity of light and magnification of the object. The light rays after reflecting from the object enter the camera where the convex lens controls the intensity of light and focuses them on the sensitive film behind the lens, the higher the intensity of light, more clearer will be the image. The image can be magnified by adjusting the focal length of the Convex lens. When the position of the object is in between the center of curvature and the focal point of the convex lens, we get an enlarged image of the object.
Telescopes are used in viewing the clear images of far-away objects. Usually, This is done by placing two convex lenses parallel to each other. The function of the first convex lens is to collect the maximum light from the source that is why it is of larger size than that of the second convex lens, which ensures a brighter image. The function of the second lens is to magnify the image. Light rays coming from distant objects are converged at a point between the focus point of the second lens and the center of curvature of the first lens, where a diminished image is formed. This image, when viewed from the second lens, appears to be magnified. This magnified image is real and inverted, but with the help of another convex lens that is placed parallel to the first two lenses, virtual and erect images can also be obtained.
A microscope enables us to see the magnified images of extremely small objects that we can not see with our naked eyes. Microscopes are made by combining two or more convex lenses that is why they are also called compound microscopes. The more the number of convex lenses used in a microscope, the more will be the magnifying power of the microscope. The simplest compound microscope consists of two lenses. The first lens, which is nearer to the object, is called the objective lens, and the second lens is called the eyepiece or ocular lens. The distance between the objective lens and eyepiece is shorter than the focal length of the eyepiece lens. The magnified image formed by the objective lens acts as an object to the eyepiece, which further magnifies this image, hence it provides the double magnified image. By using a Compound microscope, having more convex lenses, we can see the magnified images of even small microorganisms like amoeba and bacteria.
Convex lenses are also used in making Projectors. Projectors are the optical devices that project the images or videos on the screen. The main function of the projector is to provide a magnified image of the object, which can be obtained by placing the object between the center of curvature and the focal point of the convex lens. The image formed by the film or data projector is inverted that is why the film is always loaded upside down into the projector so that it can be seen the right way up on the projection screen.
8. Multi-Junction Solar Cells
Nowadays, convex lenses are used in the concentrator lens systems of multi-junction solar cells. It was tested in a 3-day study that when a convex lens is used in the concentrator lens system, 1.94% more power was produced as compared to when it was not used. A convex lens is added above the Fresnel lens, which improves the output power and reduces the need of using solar trackers. The convex lens focuses more amount of radiations on the solar cells, Which results in the increased power production.