Convex lenses

  Today you will learn the basics of convex lenses (example in the image), it will be a very simple introduction into lenses, that will help you build upon in the future.

You will be given videos and tasks about each video, whilst you are wacthing the video you should start answering the questions, as the explanation and the questions are arranged in the same order.

Watch this video:

[video:https://www.youtube.com/watch?v=K0sjZ5nqQ7g]

1.What is the focal point of a lens?

2.What is the focal length of a lens?

Watch another video: 

[video:https://www.youtube.com/watch?v=xxF_mdoZom0]

3. If the object is at a distance more than double that of the focal length, will the created image be inverted or not?

4. If the point is located at double the focal length, then what will be the distance between the center of the lens and the created image?

5.If the object is located at the focal point, what is going to happen (or what is not going to happen)?

6. Where should one place the object if he wishes to see a magnified version of it, using a convex lens.

Watch the last video:

[video:https://www.youtube.com/watch?v=7GV1UZSTNJg&t=1s]

7.What is the thin lens equation?

8. If there was a stick 1 meter from the wall, and you placed a convex lens right in the middle, between the stick and the wall, and an image of the same size as that of the stick, albeit inverted appeared on the wall, what would be the focal length of the lens?

9. You are a castaway on a very sunny tropical island, and you must make fire to survive, and it just so happens, that a lens maker ship crashed nearby and a lot of large double convex lenses were washed up. Describe the two step process of how you will get fire, using all of the knowledge you now know.

For each task you will receve one point, exept for the last one which is worth two points.

I hope that this small task helped you with the basic understanding of convex lenses.

A big thanks to Khan Academy for the videos.

The correct answers are as follows:

1. A focal point is the point at witch all rays converge.

2. Focal length is the length between the focal point and the center of the lens.

3.The image will be inverted.

4. It will be at double the focal length at the other side.

5.If the object is on the focal point, then no image will be created.

6.Between the focal point and the center of the lens.

7. A relation between the focal length, the distance of the object to the center of the lens, and the distance between the image or the converging point of the rays and the center of the lens.

8.Half of a meter.

9. First they would want to figure out the focal length of the lens(there are many ways they could do that), and then they have to hold the lens out so the distance between the easily flammable object and the center of the lens is that of the focal lenght. 

Comments: 

If they only write one of the steps in the last task they deserve one point, if they just write "hold the lens between the sun and the sticks" they deserve none.

This task has been made so that it is easy to grade it on a ten point scale.