Concave and Convex Lenses - Definition, Image Formation, Uses, FAQs
The word "lens" comes from the Latin word "lentil," which refers to the little beans that have been a staple of Mediterranean cuisine since ancient times. Because of the convex shape of lentils, their Latin name was coined for glass with a similar shape.
Lenses are used to focus or scatter light due to the way they refract light that strikes them. The composition, size, thickness, curvature, and combination of lenses employed can vary the amount of light that enters the lens in a variety of ways. Lenses are made for a variety of applications, including cameras, telescopes, microscopes, and spectacles. Other more contemporary gadgets that take advantage of lenses' capacity to diffuse or condense light include copying machines, image scanners, optical fiber transponders, and cutting-edge semiconductor fabrication equipment.
This Story also Contains
- Convex and Concave lens
- Image formation by concave lens
- Image formation by convex lens
- Difference between Concave and convex lenses.
A lens is an optical instrument that, using the concept of refraction, either converges or diverges the light beam that strikes its surface. The converging or diverging of light beams is accomplished using a piece of glass with the proper form. It is shaped so that light rays refract to generate an image.
The lens' power is measured by the amount of convergence or divergence it imparts to the light beams that pass through it.
When these lenses are used together, the result is a sharper image. Concave lenses are used in most eyeglass lenses. Different lenses are used in cameras, telescopes, and microscopes to let humans see the world more clearly.
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Convex and Concave lens
To create spherical lenses, two spherical transparent surfaces are combined. Spherical lenses can be divided into two categories. Convex lenses are made by joining two spherical surfaces that bulge outward, and concave lenses are made by joining two spherical surfaces that bend inward. The difference between concave lenses is one of the most important. Because the rays converge after passing through convex lenses, they are also known as converging lenses, whereas concave lenses are known as diverging lenses because the rays diverge after passing through them.
Rays falling on concave lenses should follow these guidelines.
1. When a beam obliquely strikes a concave or convex lens image at its pole, it continues on its path.
2. When a ray strikes concave or convex lenses parallel to the principal axis, the reflected ray travels through a focus on the principal axis.
3. When a ray passes through focus and collides with concave or convex lenses, the reflected ray passes parallel to the principal axis.
Image formation by concave lens
- A virtual image is produced at the focus when an object is positioned at infinity. The image is a fraction of the size of the real thing.
- A virtual image is produced between the pole and the focus of the convex lens when an object is positioned at a finite distance from the lens. The image obtained will be significantly larger than the object.
Image formation by convex lens
- A real and highly diminished image is produced at the focus when an object is positioned at infinity.
- A real, inverted, and diminished image is formed between F and 2F when the object is beyond 2F.
- A real, inverted, and same-size image is formed at 2F when the object is at 2F.
- A real, inverted, and magnified image is formed beyond 2F when the object is between F and 2F.
- A real and highly magnified image is formed at infinity when the object is at F.
- A virtual, erect, and magnified image is formed on the same side of the lens when the object is between F and the optical center (O).
Difference between Concave and convex lenses.
|
Properties |
Concave lens |
Convex lens |
|
Look |
The middle of a concave lens is thinner, while the edges are thicker. |
The middle of a convex lens is thicker than the edges, while the margins are thinner. |
|
Also known as |
Diverging lenses |
Converging lenses |
|
Focal length |
Negative |
Positive |
|
Incident rays |
The incident rays are diverged away from the main axis. |
The incident rays converge towards the primary axis. |
|
Applications |
Used in glasses, some telescopes, and door spy holes, among other things. It's also utilized to remedy a problem with short-sightedness. |
Used in cameras, overhead projectors, projector microscopes, basic telescopes, magnifying glasses, and other devices. It can also be used to correct a long-sightedness condition. |
NCERT Physics Notes :
Uses of Concave Lens:
Concave lens used in glasses. Concave lenses are most commonly used to correct myopia, which is also called near-sightedness.
- Uses of concave lenses in lasers.
- Use of concave lenses in cameras.
- Used in flashlights.
- Concave lens used in peepholes.
Uses of convex lens:
- Used in cameras to focus and magnify images for clear photos and videos.
- Helps correct farsightedness by focusing light on the retina.
- Enlarges the outside view in peepholes for security.
- Magnifies tiny objects in microscopes for observation.
- Enlarges small objects or text with a magnifying glass.
- Projects enlarged images or videos on screens in projectors.
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Commonly Asked Questions
The main difference lies in their shape and how they affect light rays. Concave lenses are thinner in the middle and thicker at the edges, causing light rays to diverge. Convex lenses are thicker in the middle and thinner at the edges, causing light rays to converge.
A simple way to remember is the "cave" in concave. Imagine a cave curving inward, like the surface of a concave lens. Convex, on the other hand, bulges outward like the outside of a cave.
Yes, a convex lens can form both real and virtual images depending on the object's position relative to the focal point. When the object is beyond the focal point, it forms a real image; when it's within the focal point, it forms a virtual image.
The focal point is the point where parallel light rays converge after passing through a convex lens, or from where they appear to diverge after passing through a concave lens.
The focal length of a lens is inversely proportional to its curvature. A lens with a greater curvature (more curved surface) has a shorter focal length, while a lens with less curvature has a longer focal length.
Frequently Asked Questions (FAQs)
Concave mirrors and convex lenses both converge light rays, causing them to meet at a focal point. This similarity in light behavior leads to comparable image formation properties, including the ability to form both real and virtual images depending on object position.
Concave lens: Diverging lens, always gives virtual, erect, diminished images. Uses: spectacles for myopia, peepholes.
Convex lens: Converging lens, can form both real and virtual images. Uses: microscopes, cameras, magnifying glasses.
Concave lens: Diverging, always forms small, virtual, erect images.
Convex lens: Converging, can form real/inverted or virtual/magnified images.
A convex lens can form real, inverted images when the object is outside focus, and a virtual, erect, magnified image when the object is between focus (F) and optical center (O).
A concave lens ray diagram shows light rays diverging after refraction, with their backward extensions meeting to form a virtual, erect, diminished image.
Monochromatic aberrations occur with light of a single wavelength and include spherical aberration, coma, and astigmatism. Chromatic aberrations result from the lens's different refractive indices for different wavelengths of light, causing colors to focus at different points.
Wavefront shaping involves manipulating the phase of light waves to control their propagation. In lens design, this concept is used to create advanced optical elements that can correct aberrations or create specific light patterns, potentially improving image quality beyond what's possible with traditional lenses.
Principal planes are imaginary planes in a thick lens system where paraxial rays appear to bend. They are important for simplifying calculations in thick lens systems and understanding how light behaves when passing through multiple lenses.
Cylindrical lenses focus light to a line instead of a point. They have curvature in only one direction, making them useful for correcting astigmatism in vision or creating line focuses in certain optical systems.
Paraxial rays are those that travel close to and nearly parallel to the optical axis, while marginal rays are those that pass through the edges of the lens. Paraxial rays are used in simple lens calculations, but marginal rays are important for understanding aberrations and real lens behavior.