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To Find Image Distance for Varying Object Distances of a Convex Lens With Ray Diagrams

Last updated date: 18th Jul 2024
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Physics Experiment- To Find Image Distance For Varying Object Distances of a Convex Lens With Ray Diagrams - Introduction

A transparent material is bound by two surfaces to form the lens. It has an optical centre, an aperture, a principal axis, a principal focus, and a lens's centre of curvature. There are two different kinds of lenses: convex lenses and concave lenses. These lenses can produce real or virtual images, depending on the user. In this article, we will be focusing on the images formed by the convex lens.

The centre of a convex lens is thicker in the middle, also known as a converging or positive lens. In a convex lens, light rays converge or are brought closer together. A convex lens can be used in various applications, such as a microscope, magnifying glasses, a camera, the treatment of hypermetropia, etc.

Table of Content

  • Introduction

  • Aim

  • Theory

  • Procedure

  • Observation Table

  • Result

  • Lab Manual Questions 


To determine the image distance for various object distances while using a convex lens and to depict the relevant ray diagrams to demonstrate the nature of the image created.

Apparatus Required

Here are the supplies you'll need for the experiment:

  • Convex lens with 12–20 cm focal length

  • Measuring scale

  • Optical workbench

  • The needle

  • Sticky tape or drawing pins

  • A candle

  • A drawing board

  • A white paper


A convex lens is thick in the middle and thin at the edges. This lens focuses the light beam that strikes it; as a result, it is sometimes referred to as a converging lens.

The image distance formula or lens formula is as follows:

\[\dfrac{1}{f} = \dfrac{1}{v} - \dfrac{1}{u}\]

Where distance formula in an experiment with a lens the object distance u, v denotes the image's separation from the optical centre, and f denotes the lens's focal length


  1. Convex lenses should be mounted on holders with the screen on the opposite side (as shown in the experimental setup).

  2. To get a clear, inverted image on the screen, try focusing the image. It is possible to measure the focal length using a metre scale as it is only an approximate measurement.

  3. Make a "C" in the location where the lens is fixed.

  4. Mark point F on both sides of the lens once you've computed the focal length.

  5. Point 2F should be noted because the distance between the lenses is twice their combined focal length.

  6. Place the candle farther away than 2F and align the height of the lens's centre with the flame's height.

  7. Adjust the screen's position and take notes after getting a clear image of the candle flame through the convex lens.

  8. Place a needle or lit candle at 2F to record the observations.

  9. You can record your observations by moving the object between F and 2F.

  10. By setting the object to F, you can record your observations.

  11. Place the thing between C and F and note the observations below.

  12. Make ray diagrams for each point of the object.

Experimental setup to perform the experiment

Experimental setup to perform the experiment

Image formation by Convex lens

Image formation by Convex lens

Convex lens ray diagram

Convex lens ray diagram

Observations Table

Sr- No.

Position Of The Optical Center C Of The Lens l (cm)

Position Of The Candle a (cm)

Position Of Screen s (cm)

Distance Between Lens And Candle (object distance) u=a-l (cm)

Distance Between Lens And Screen (image distance) v=s-l (cm)

Focal length f (cm)







Table 2. Observed results from images.

Sr- No.

Position Of The Object

Position Of The Image

Relative Size Of The Image

Nature Of The Image


At 2F1

At 2F2

Same size

Real and inverted


Between Fand 2F1

Beyond 2F2


Real and inverted


Beyond 2F1

Between F2 and 2F2


Real and inverted


At focus F1

At infinity

Infinitely large or highly enlarged

Real and inverted


Between focus Fand optical centre O

On the same side of the lens as the object


Virtual and erect


At infinity

At focus F2

Highly diminished, point-sized

Real and inverted

The object distance image distance focal length are all measured from the image as shown above. The lens that is being used has a 10 cm focal length.


  1. The experiment should be carried out in a steady space that will prevent the candle flame from flickering. This will also help in producing a non-shaky image. 

  2. Parallax should be avoided when taking the reading. 

  3. The object and the screen should all be on the same horizontal axis.

Lab Manual Questions 

  1. Why do we use ray diagrams for convex lenses?

Ans: To determine the image distance for various object distances and to depict the relevant ray diagrams to demonstrate the nature of the image created.

  1. How can ray diagrams be used to observe image distance for various object distances?

Ans: Using the converging nature of the convex lens. The lens focuses on the light beam that strikes it.

  1. How can one determine a convex lens image distance?

Ans: Using the lens formula is given by the equation: 

\[\dfrac{1}{f} = \dfrac{1}{v} - \dfrac{1}{u}\]

where v is the image's distance from the optical centre, f is the lens's focal length, and u is the object's distance from the optical centre.

  1. How do you conduct an experiment with convex lenses?

Ans: Fix the narrow convex lens to the lens holder and observe the outcomes. After that, apply the Lens formula. 

Viva Questions

  1. How do lenses work?

Ans: Lenses are transmissive optical devices to focus or scatter light beams through refraction.

  1. How many lenses are present in a basic lens?

Ans: A straightforward lens is made of a solitary clear piece.

  1. What number of lenses does a compound lens have?

Ans: A compound lens is created by aligning numerous basic lenses along a central axis.

  1. What categories of lenses exist?

Ans: Convex and concave lenses fall into categories.

  1. Describe a convex lens.

Ans: A convex lens is defined as thick in the middle and thin at the edges.

  1. Describe the lens formula.

Ans: The lens formula is given by the equation: 

\[\dfrac{1}{f} = \dfrac{1}{v} - \dfrac{1}{u}\]

  1. What other names are used for convex lenses?

Ans: Converging lens.

  1. What other names are used for concave lenses?

Ans: Diverging lens.

  1. What is an optical centre?

Ans: The optical centre refers to the location on the primary axis in the middle of the lens.

  1. What kind of convex lens is it?

Ans: There are three varieties of convex lenses:

  • Double convex lens

  • Plano-convex lens

  • Concavo-convex lens 

Practical Based Questions

1. What is the term for a wave's shift in direction as it travels from one medium to another?

  1. Interference

  2. Mirage

  3. Diffraction

  4. Refraction

Ans: D) Refraction

2. If a light ray had no angle of reflection, what would be its angle of incidence?

  1. a 180° angle

  2. a 90° angle

  3. a 0° angle

  4. a 45° angle

Ans: C) a 0° angle

3. Which of the following phenomena allows light to be focused on our retina?

  1. Interference

  2. Refraction

  3. Diffraction

  4. Mirage

Ans: B) Refraction

4. What is the symbol for the speed of light in a vacuum?

  1. a

  2. v

  3. c

  4. l

Ans: C) c 

5. What can be employed to see the complete length of an image of a faraway tall building?

  1. a convex mirror

  2. a plane mirror

  3. a concave mirror

  4. none of the options

Ans: A) Convex mirror

6. Which law states, “There is a continuous relationship between the sine of the angle of incidence and the sine of the angle of refraction”?

  1. Faraday’s law

  2. Snell’s law

  3. Newton’s law

  4. Murphy’s law

Ans: B) Snell’s Law 

7. The twinkling of stars is due to which optical phenomenon?

  1. Reflection

  2. Interference

  3. Refraction

  4. Divergence

Ans: C) Refraction 

8. The principles of reflection are applicable for

  1. a convex mirrors

  2. a plane mirrors

  3. a concave mirrors

  4. all mirrors irrespective of their shape

Ans: D) all mirrors irrespective of their shape

9. What is the point at which sunlight reflected by a convex lens converges?

  1. Radius of curvature

  2. Optical centre

  3. Focus

  4. None of the options

Ans: C) Focus

10. Concave lenses generate

  1. only virtual images

  2. only erect images

  3. only diminished images

  4. virtual, erect, and diminished images

Ans: D) virtual, erect, and diminished images


In this experiment nature, size, and location of the image at a certain object distance through a convex lens are examined. The Lens formula is further discussed with the object position, focal length, and image magnification. The nature and position of the image produced by a lens can further be shown in the ray diagram of convex lens above.

FAQs on To Find Image Distance for Varying Object Distances of a Convex Lens With Ray Diagrams

1. Mention a few applications for convex lenses.

Plano-convex lenses are used in telescopes, cameras, microscopes, magnifying glasses, and to treat hypermetropia.

2. Describe an aperture.

An aperture is the region of a spherical surface from where light is refracted.

3. Can genuine images be formed using convex and planar mirrors? Give a justification for your response.

The light beams that converge behind a plane mirror or convex mirror are reflected onto a screen at a position in front of the mirror. In other words, if the object is virtual, a planar or convex mirror can produce a genuine image.

4. Do people refer to convex as a converging lens or a diverging lens?

Converging lenses converge the light rays that are heading their way, whilst diverging lenses diverge the rays that are coming their way. A genuine image is created by convergent lenses, but a virtual image is created by divergent lenses. Convex lenses may diverge in this situation. Another name for a convex lens is a converging lens.