What is Convex lens: Definition and 58 Discussions

A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (elements), usually arranged along a common axis. Lenses are made from materials such as glass or plastic, and are ground and polished or molded to a desired shape. A lens can focus light to form an image, unlike a prism, which refracts light without focusing. Devices that similarly focus or disperse waves and radiation other than visible light are also called lenses, such as microwave lenses, electron lenses, acoustic lenses, or explosive lenses.
Lenses are used in various imaging devices like telescopes, binoculars and cameras. They are also used as visual aids in glasses to correct defects of vision such as myopia and hypermetropia.

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  1. Overdose_

    Finding the focal length of a converging lens with VERY limited info

    This is the solution but I do not understand??? How could they just assume the object distance equals 2f? No magnification is given here. We know the candle produces a real image and the distance is limited, so that means it must be somewhere between the principal focus, the center of curvature...
  2. Lotto

    Calculate the focal length of a thin convex lens

    My picture is here: The diameter ##D## is also a diameter of the lens. If there was no shade, the image of the moved source would be by using ##\frac{1}{2f}+\frac{1}{L}=\frac 1f## at a distance ##L=2f##. So by using a triangle similarity we get ##\frac{D/2}{L}=\frac{d/2}{L-l}##, so...
  3. B

    An ambigious optical system with ambigious solutions [JEE Adv - 20`16]

    This problem was asked in one of the most prestigious exams in India: JEE Advanced, unfortunately it was considered to be ambiguous for the scope of given examination and hence no official answer is issued for it as such.(BONUS marks to all) And so many solutions were posted on Internet which...
  4. fernelau

    Understanding the Impact of Convex Lens Focal Length on Water Temperature

    Summary: Hi, I'm doing an assessment for Physics on Optics topics, but I can't really explain how the CV affect the RV CV : Focal length of convex lens RV : Temperature of water after 20 minutes under the sun How I should explain for the temperature difference? 🤔 Please help, Thanks.
  5. Krushnaraj Pandya

    Splitting of a convex lens problem

    Homework Statement A thin convex lens of focal length 20 cm is split into two parts along the principal axis, now there is a 2mm gap between the top and bottom parts, an object O is placed at 10 cm from the lens, the distance between the two virtual images will be? Homework Equations 1/v - 1/u...
  6. N

    The use of plano convex lens in a slide projector

    Hello My question has two parts: 1) Why is plano convex lens used in slide projector? Why can't we use simple convex lens in it? 2) Why are two plano convex lenses used in slide projector? Why can't we use only one?Thanks!
  7. F

    Double slits and convex lens interference

    Homework Statement Two slits (of width ##a=39 \mu m##) are lighted up with a monocromatic wave of ##\lambda=632,8 nm##. The distance between slits and the screen id ##D=4 m##. The distance between the slits id ##d=195 \mu m##. In front of the slits there are a convergent lens with focal length...
  8. J

    Photoelectric current and a convex lens

    Homework Statement Homework EquationsThe Attempt at a Solution The photoelectric current is directly proportional to the intensity of the light falling on it . It will not depend on the focal length of the lens . When the lens of half the diameter is used , intensity is halved . This...
  9. Hydrous Caperilla

    Simple microscope and convex lens

    When does a convex lens behhave as a simple microscope and what are the conditions for the object and the lens to act if there are any?Is the magnifying power of microscope fixed beyond which it will act as a regular convex lens
  10. Rheegeaux22

    Help With a Difficult Lenses Question: Find the Answer!

    Homework Statement The question is : https://postimg.org/image/lntyejfvp/ Homework Equations 1/s +1s' =1/f The Attempt at a Solution Hello, I have an upcoming test on Monday on lenses and while reviewing I've come across a question that confused me. My understanding is that the image of...
  11. Deebu R

    Find the Power of a Bi Convex Lens

    Homework Statement If the focal length of the bi convex lens is 25 cm then the power of the lens will be? Since the light striking the lens converges at a point behind the lens will the answer come in positive? Homework Equations Power of lens D= 1/f The Attempt at a Solution D= 1/25= +0.04...
  12. A

    Forming an Image with a Convex Lens

    Using a convex lens, can an image be formed at the focal point and if so where would the object have to be from the convex lens?
  13. P

    5 Questions dealing with Optics, image included

    1. A real inverted image I of an object O is formed by a certain lens (not shown); the object—image separation is d = 40.0 cm, measured along the central axis of the lens. The image is just half the size of the object, a. What kind of lens must be used to produce this image? b. How far from the...
  14. S

    Image formation by convex lens

    What will happen if look at(or in the direction of) a distant object through a convex lens?
  15. N

    Convex Lens: Image Formation at Infinity & Parallel Rays

    For an object at focal length in front of a convex lens, the image formed will be at infinity and the refracted rays are parallel (refer to the figure). Since our eye lens is convex in nature, why don't it converge these parallel rays so that an image can be formed?
  16. 0

    Determining the light intensity in a double convex lens

    Attached is an illustration of an image being demagnified using a double convex lens. I want to determine the intensity of the light (mW/cm2) if I were to put a lux meter at various locations after the convex lens given that the object is at a fixed location. The object is a monochromatic light...
  17. Siddharth Venu

    Convex Lens Problem: Find Focal Length

    A screen is placed 90cm from a object. The image of the object on the screen is formed by a convex lens at two different locations separated by 30cm. The focal length of the lens is what?
  18. R

    Need Aspherical Lens Equation (+20d, 55mm)

    Hello. I am not related to physics or any optics related field. I am in need of equation for +20d aspherical lens of diameter 55mm. Can anybody help me?
  19. N

    I Double slit particle distribution with convex lens?

    In one double slit experiment, one physicist placed a convex lens before the back screen detector. The individual photons passed through the double slit then through the lens. The individual photons then go through the focal point, then a good distance after they reach the focal point they hit...
  20. J

    Help please -- convex lens problem and focul length

    Homework Statement Suppose the convex lens is placed at the 49.4 cm mark, and an image forms on the screen at the 70.5 cm mark. Find: A) The focal length of this lens: ____ cm B) the absolute value of the magnification of this lens: ________ C) the height of the image: ________cm Homework...
  21. S

    How to Obtain a Magnification of -2 from a Convex Lens?

    Homework Statement You wish to obtain a magnification of -2 from a convex lens of focal length f. The only possible solution is to: A) place a virtual object at a distance 2f/3 from the lens. B) place a virtual object at a distance 5f/3 from the lens. C) place a real object at a distance...
  22. Z

    Lens Question for Design of an Infrared Spotlight

    Hello All. I'm working on a project to build an infrared spotlight which will hopefully light up a distant object so that I can see it on an IP enabled night vision camera. The lens problem seems very straight forward, but I could use some help. Per the attached diagram, I want to focus the...
  23. Prashasti

    Finding Focus Length in Broken Double Convex Lens

    Homework Statement A thin double convex lens of focal length f is broken down into two halves at the axis. The two haves are then combined, as shown in the figure. What will be the focal length for the arrangements...
  24. AwesomeTrains

    Ray transfer matrix - Plano convex lens

    Homework Statement I have to find the ray transfer matrix for a Plano convex lens, with a 5 cm radius and refraction index n=1.8. I'm supposed to use the paraxial approximation. Attached a homemade picture of the lens. Homework Equations Refraction at a curved surface: \begin{pmatrix} 1 & 0\\...
  25. S

    Silvering of Plano-Convex Lens

    If the plane surface of a plano-convex lens in silvered then which of the following statements is true? 1. it acts like a convex mirror 2. it acts like a concave mirror 3. it acts like a concave lens 4. no changemy attempt--- the incident ray on the convex surface of the plano-convex will...
  26. AdityaDev

    Can a Convex Lens Converge a Tilted Wavefront?

    If I have a parallel beam of light parallel to x-axis, with the speed of light varying from bottom to top. Let it decrease from bottom to top. (To get such a beam one can pass the beam through a glass slab normal to its surface, whose refractive index increases linearly from bottom to top). Now...
  27. T

    Ray Tracing for Convex Lens: How to Determine Image Distance and Realness

    Homework Statement [/B] B) Is the image real or virtual? Explain. C) Using the lens equation, find the image distance. 2. Homework Equations 1/di + 1/do = 1/f The Attempt at a Solution A) B) The image is real because it is on the opposite side of the lens as the source of light. C) do =...
  28. M

    Image seen by human eye through a convex lens

    Greetings, I don't have a magnifying glass/convex lens otherwise I would try to confirm this by experiment. Maybe I'll get one soon but to get things started. Let's say you have an object, with its own light source, and a convex lens with focal point f. The object is beyond 2f away from the...
  29. B

    Focal Length of a Plano Convex Lens

    Hi, The focal length of the Plano-Convex lens as calculated by the lens maker equation: Does it work when light crosses the lens from the convex side, planar side, or both? Thanks.
  30. L

    Orientation of Image Produced by Double Convex Lens

    This is not really a problem, more just a fact-based question. I have been using the Google, but I have been unable to find an answer. Is there a way to induce the answer that I am missing? :confused: Question: What range of distance does a double convex lens have to be from an object to...
  31. L

    Image of a Convex Lens Cut in Half Horizontally

    Hello everyone, A friend of mine came up with this question in class and I really do not have a good answer. Suppose you have a convex lens that has been cut in half horizontally and the top half removed. The question is: Will the bottom half of the lens still form an image? I really...
  32. A

    WHY does curvature of a convex lens affect focal length?

    Homework Statement For my high school physics coursework I must investigate factors affecting the focal length of a lens. I have focused on radii of curvature and completed my data collection and verified the accuracy using the lens makers equation. However, in the conclusion I am really...
  33. C

    Does a Convex Lens Cause Eye Heat When Viewing a Light Source?

    I was just wondering if a person wearing convex lenses looks at a light source... Will excess heat be generated in his eyes? As it is a converging lens.. Thanks!
  34. R

    Why Does a Ray of Light Not Get Refracted at the Optical Center of a Convex Lens?

    I'd like to know why a ray of light passing through the optical center of a convex lens does not get refracted at all. According to my knowledge, a ray of light will not get refracted if the angle of incidence is zero i.e. it is along the normal. With this in mind, I see how a ray traveling...
  35. A

    Focal length calculations for a double convex lens?

    From what I recall, determining the focal length of a double convex lens just involves an infinite light source and holding the lens close to an image-capturing surface such as a wall and adjusting the distance until the image is at its sharpest...the distance from the lens to the surface is the...
  36. Y

    What is the Focal Length of a Convex Lens?

    I am trying to find the focal length of a convex lens, so i let the sun shine through my window to create an image on my wall. Is that image the focal point or is it just the distance of the image? And if it is the distance of the image, how do I put it into the thin lens equation, since the...
  37. Y

    Difference between convex lens formula and convex mirror formula

    Homework Statement difference between convex lens formula and convex mirror formula The Attempt at a Solution for convex mirror you make focal point negative and use the 1/f = 1/do + 1/di but for convex lens do you do the same? you don't make the f negative i think am i...
  38. I

    Diamond Ring in Front of a Convex Lens?

    Homework Statement A 1.5 cm high diamond ring is placed 20 cm in front of a convex lens whose radius of curvature is 30 cm. a) What is the position and the size of the image? b) What magnification does this lens have? Homework Equations 1/f= 1/di + 1/do m= -di/do or hi/ho The Attempt at a...
  39. D

    Finding Convex Lens Focal Length

    Homework Statement Following data recorded: Di (distance image to lens) 6.0 8.0 10.0 12.0 14.0 Magnification 0.2 0.6 1.0 1.4 1.8 Graph magnification against di and use the graph to find the focal length of the lens. Homework Equations...
  40. S

    Why Is an Image at Infinity Called Highly Magnified?

    When an object is placed at the focal point of a convex lens, the image is formed at infinity, yet it is called a highly magnified image. The fact being that after passing through the convex lens the rays run parallel or rather as a beam. My question is that if the image is formed at...
  41. M

    Ray Diagram: Small Bulb & Convex Lens

    Homework Statement A small bulb is placed in front of a convex lens. a) Suppose that the bulb is placed as shown. Using all three principal rays, draw an accurate ray diagram to determine the location of the image. Label the image location...
  42. C

    Finding the thickness of a double convex lens

    Homework Statement A double convex lens has a diameter of 5 cm and zero thickness at its edges. A point object on an axis through the center of the lens produces a real image on the opposite side. Both object and image distances are 30 cm, measured from a plane bisecting the lens. The lens has...
  43. S

    Convex lens questionCant find the equation i need. Please help

    A convex lens of focal point 0.8m focuses a real image of the moon onto a screen. If the moon subtends an angle of 0.5 degrees to an observer on earth, calculate the size of the moons image on the screen? Thats the question guys, I am really struggling to find the appropriate equation as we...
  44. A

    How Does Bisecting a Lens Affect Its Focal Length?

    1)Why when a convex lens having radius of curvature R, focal length f and refractive index μ is bisected horizontally along the principal axis its focal length remains the same, whereas when it is bisected vertically focal length becomes 2f? Does the same thing happens in the case of...
  45. N

    Solving for p: Finding Distance from Convex Lens

    Homework Statement Given only the distance between the object and its image (p +q), how is it possible to find p, the distance of the object from the convex lens? Homework Equations 1/p + 1/q = 1/f in this case, p + q =40 also, the image is smaller than the original, so p > 2f The...
  46. G

    Magnification in a Convex Lens: + or -?

    In a conversing lens, if the object is not within the focal point, then the magnification is "-". But in the case where the object is placed in the focal point, then the magnification is "+"?
  47. G

    Creating an Image 2x Size of Object w/ Convex Lens: Half Focal Length Away

    Homework Statement A converging lens (convex lens) creates an image that is 2 times the size of the object. The object is placed: Homework Equations -di/do = hi/ho 1/f = 1/di + 1/do The Attempt at a Solution I thought the answer was that the object is place two focal lengths...
  48. J

    Find the focal length of a concave lens using a convex lens?

    Can anyone explain to me the procedure that one would follow to you find the focal length of a concave lens using a convex lens? Thanks.
  49. P

    Convex Lens and Light Refraction

    Hi all, if light was to go straight through a convex lens would it come out straight or inverted to a point? also if light was to go through the same lens but goes through going inwards how would the light be refracted?
  50. X

    Determining Focal Length of Convex Lens Without Apparatus

    So I got a lab to plan and design an experiment to determine the focal length of a convex lens and involve the use of lens eq. and by means of plotting a graph...I have a basic rundown of what needs to be done and all but I am somewhat in a dilemma i don't have any access to any of the apparatus...
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