If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Course: Class 10 Physics (India)>Unit 1

Lesson 11: Image formation by spherical lenses

Convex lenses

This video explores the concept of convex lenses, focusing on how they refract and transmit light. The instructor explains the behavior of light as it passes through a lens, using the analogy of a car to illustrate refraction. The video also introduces the idea of a lens's focal point and the thin lens assumption. It concludes with a demonstration of how lenses form real, inverted images. Created by Sal Khan.

Want to join the conversation?

• If i combine 2 of such convex lenses, how does the image of the 1st lens act as the virtual object for the second lens?
its like real==>real==>virtual==>virtual
its kinda complicated to explain with mere typing.
• a double convex lens silvered at one surface behaves like a concave mirror.how?
• Silver Coating will reflect the light rays and will not allow the light rays to pass through the Convex lens to Converge.
In this case the convex lens acts as if a Convex mirror. It diverges the light rays. The Focus point is on the another side of optical center.
• Does our eye lens contain convex lens?
• yes, it is a convex lens. it is needed to focus, on any image because, the rays coming are scattered and all rays need to be pointed at a specific point on retina for a image to be formed in our brain.
• How do we draw the refracted rays? Are they to be randomly drawn?
• Firstly, you draw a normal where the incident rays hit. (A line at 90 degrees)
Secondly, measure the angle of incident rays.
Finaly, draw a line the exact angle of incident rays.

Hope this helps!
• does this mean that everything we see is upside down?
(as our eyes have convex lenses)
• I think you are getting the physical process of the light getting to the retina with your perception of the image.

The image that gets to the retina of your eye is upside down but that is not how your brain perceives the image.

There has been an experiment where the subjects were given glasses that inverted the image they saw that they kept on while they had their eyes open. Initially it was very disorienting but after about a week their brains had adjusted to the inverted image and they were able to function normally like before they put on the glasses. At the end of the experiment when they took off the inverting glasses again it took about a week for them to adjust to their "normal" vision.
• Why do we use two rays from the same point on an object to construct ray diagrams?
• minimum two rays are required, u can use more. Also the image is located where the two rays meet.
• What happens if I pass light through the centre of the lens, between the two poles?
• It would pass without any deviation, through the focus.
• How many images are formed when two mirrors are kept parallel.
• infinite......
• I still struggle to get intuition for real and virtual images. How can I tell the difference? What do they look like in real life?
• good question.

I find it easiest to think it this way...

a real image can be seen on a screen. (such as a wall or piece of paper etc)
but a virtual image can not be put onto a screen. you can see it in your eye but not on a screen

ok?
• Would there be a focal point if the curvature of the lens wasn't circular?

Also, regarding how the negative and positive focal points are the same distance from the lens, does that assume that the lens is symmetrical?

(A lot of pics of eye anatomy that I've seen make it look like the lens of the eye isn't quite symmetrical...?)