<< Chapter < Page Chapter >> Page >
A double convex lens is a converging lens.

[link] shows a convex lens. Light rays traveling through a convex lens are bent towards the principal axis. For this reason, convex lenses are called converging lenses.

Light rays bend towards each other or converge when they travel through a convex lens. F 1 and F 2 are the foci of the lens.

When an object is placed in front of a lens, the light rays coming from the object are refracted by the lens. An image of the object is produced at the point where the light rays intersect. The type of images created by a convex lens is dependent on the position of the object. We will examine the following cases:

  1. the object is placed at a distance greater than 2 f from the lens
  2. the object is placed at a distance equal to 2 f from the lens
  3. the object is placed at a distance between 2 f and f from the lens
  4. the object is placed at a distance less than f from the lens

We examine the properties of the image in each of these cases by drawing ray diagrams. We can find the image by tracing the path of three light rays through the lens. Any two of these rays will show us the location of the image. The third ray is used to check that the location is correct.

Experiment : lenses a


To determine the focal length of a convex lens.


  1. Using a distant object from outside, adjust the position of the convex lens so that it gives the smallest possible focus on a sheet of paper that is held parallel to the lens.
  2. Measure the distance between the lens and the sheet of paper as accurately as possible.


The focal length of the lens is                       cm

Experiment : lenses b


To investigate the position, size and nature of the image formed by a convex lens.


  1. Set up a candle, and the lens from Experiment Lenses A in its holder and the screen in a straight line on the metre rule. Make sure the lens holder is on the 50 cm mark. From your knowledge of the focal length of your lens, note where f and 2 f are on both sides of the lens.
  2. Using the position indicated on the table below, start with the candle at a position that is greater than 2 f and adjust the position of the screen until a sharp focused image is obtained. Note that there are two positions for which a sharp focused image will not be obtained on the screen. When this is so, remove the screen and look at the candle through the lens.
  3. Fill in the relevant information on the table below
Experimental setup for investigation.


Relative position of object Relative position of image Image upright or inverted Relative size of image Nature of image
Beyond 2 f         cm
At 2 f
Between 2 f and f
At f
Between f and the lens


  1. When a convex lens is being used:
    1. A real inverted image is formed when an object is placed                      
    2. No image is formed when an object is placed                      
    3. An upright, enlarged, virtual image is formed when an object is placed                      
  2. Write a conclusion for this investigation.

Experiment : lenses c


To determine the mathematical relationship between d 0 , d i and f for a lens.

Questions & Answers

What is a vector
Mercii Reply
vector is anything that has both a direction and a magnitude .they are usually drawn as pointed arrows ,the length of which represents a vector's magnitude
what is electronics?
how to calculate the reading on voltmeter or ammeter
mosima Reply
why is HCl considered a strong acid
Sphiwe Reply
it dissociate almost completely
what is metal displacement
Andile Reply
what is an electric field?
Noluthando Reply
is the charge of an electron always 1,6 ×10^-19? and the mass is always 9,1×10^-13?
Neo Reply
how to calculate a distance between charges
Celucolo Reply
juss apply the formula of the Electrostatic force
how to show polarity
Sandiso Reply
what can ii do to pass physics
Slindile Reply
Use previous years question papers to understand how questions are answered and asked
but it hard ii am a slow learner
Then the best thing to do is that immediately you are done reading through a certain topic, and you think you understood everything in that topic that's when you can use previous question papers and answer questions related to the topic. I think that's not difficult
mm ii will try
Here's a tip in reading textbooks, don't read it like a novel. First, flip through the pages—scan the chapter that you wanted to read. Second, go to the end of the chapter. Usually, there's a quiz at the end, so if will give you the important information that you need to know.
Third, go to the beginning of the chapter and read through the words that were printed in bold: Titles, subtitles, headings, important words —because it helps to break down information.
Fourth, read the first sentence of the chapter—if it is written by a good author; therefore, it will also have a good introduction. Check also the last sentence of the chapter to sum it up. Finally, read the whole chapter. You won't read it twice anymore.
It looks hard, cause there are so much to do but read it thoroughly, it's easy and it will help you to save time and comprehend better. If you don't really have interest on reading—there are various of videos in youtube😊
Oh, so em dashes turn into question marks :' (( nvm. Goodluck to all of us!
How many ways can we calculate the empirical formula
Joseph Reply
How is current divided between resistors in parallel
ii know 2 ways
what's the other way
What is the meaning of Coulomb's law
Nozipho Reply
Electronic magnetic field
Pride Reply
what is an emf ?
Nobuhle Reply
electromotive force
what are moments of a force
Mercy Reply
the moment of a force" is a measure of a tendency to cause a body to rotate about a specific point or axis....a moment is due to force not having equal and opposite force directly along its line of action.
how to calculate the magnitude of the force of repulsion
Vicky Reply

Get the best Siyavula textbooks: gr... course in your pocket!

Source:  OpenStax, Siyavula textbooks: grade 11 physical science. OpenStax CNX. Jul 29, 2011 Download for free at http://cnx.org/content/col11241/1.2
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Siyavula textbooks: grade 11 physical science' conversation and receive update notifications?