Let us learn about different types of lenses, concave and convex lens. We know about glasses used in spectacles to see near and far objects and magnifying glasses to see very small objects. These glasses are called lenses. In fact, a spherical lens is a piece of transparent refracting material that is usually glass which is bound by two curved surfaces or by one curved and one plane surface.

 

Types of commonly used spherical lenses-

 

1. Concave lens
2. Convex lens

 

Concave Lens

 

A concave lens is a diverging lens that works similarly to the convex mirror. This lens is thicker towards the edges and thin at the center. You might have observed that images formed by peepholes are different from the images formed by the normal mirrors. This is because the peephole contains concave lenses. You might have seen some of your friends using specs to see far objects. Actually, these spectacles contain concave lenses.

 

Convex Lens

 

You have learned about the concave lens. Now, let�s learn about the convex lens. A convex lens is the most commonly seen type of lens. A convex lens is a converging lens that works much like a concave mirror. This kind of lens is thicker in the middle and thinner towards the edges.

 

A convex lens makes the object appear magnified when viewed through it. You might have seen the magnifying glasses used to read the very small print. You might have also used it to observe the body parts of a cockroach or an earthworm in your school lab.

 

The shape of the lens used in our eyes is also convex. You might have seen your grandfather using specs to read the newspaper. The lens used in his specs is also a convex lens. You would be wondering why these lenses are called converging lenses.

 

Let�s do an activity to understand it. This activity should be performed in the presence of an elder. Take a convex lens. Put it in the path of sun rays. Place a sheet of paper as shown here. Adjust the distance between the lens and the paper. Hold the lens and the paper in this position for a few minutes. You will find that the paper begins to burn. Why does this happen? Because light and heat rays from the sun converge at a point on the sheet of paper and eventually begin to burn it.

 

Application of lenses

 

You have studied types of lenses. Now, let�s see their applications in different fields.

 

1. You know that a convex lens makes the object appear magnified when viewed through it. Hence, a convex lens is widely used in magnifying glasses.
2. You might have used these glasses, in your school lab for examining body parts of cockroaches, earthworms, and other minute structures.
3. A convex lens is also used in specs of those people who cannot see near objects clearly.
4. You might have seen how the watch repairer manages to fix tiny parts in the watch. Actually, the eyepiece of the watch repairer contains a convex lens that magnifies the image of the parts of the watch.
5. Convex lenses are frequently used in cameras, microscopes, and projectors, etc.

 

Now let�s see the uses of a concave lens.

 

A concave lens can be used in spec to correct nearsightedness. A peephole, such as you would find in the door, uses a concave lens to make the small size erect image of the person standing outside. Concave lenses are mostly used in binoculars and telescopes.

 

Images formed by concave and convex lenses

 

You have experienced that when light rays from the sun pass through a convex lens converge at a point forming an image of the sun as a bright spot. What will happen if you use a concave lens? When light rays are incident on a concave lens, they diverge or bend outwards. Let�s do an activity to observe how images are formed by concave and convex lenses.

 

First, fix a convex lens on a stand and place it on a table. Take a paper screen and fix it too with a stand. Now, keep a lighted candle on the table at a far-off point from the lens. You may have to move the screen towards or away from the lens to get a sharp image of the flame.

 

You will find a real, diminished, and inverted image Now, move the candle towards the lens, you will find the image is getting larger. Now, place the candle very close to the lens. You will see an erect and magnified image. This image will not appear on the screen as it is a virtual image.

 

Now, study the images formed by a concave lens. If you place the candle close or away from the concave lens, you will always see an erect and smaller image than the object. You cannot have this image on the screen as it is a virtual image of the object. Now, you see that the images formed by the concave lens and convex lens are of different types.

 

Read More- Concave and Convex Mirror - Definition, Properties, & Image Formation