00:01
Let's start by writing down the information available to us.
00:04
So we have that the focal length of our first converging lens is three centimeters.
00:14
And the distance from our object to that first lens is four centimeters.
00:21
We also know that the focal length of our second lens is negative five centimeters because it's a diverging lens.
00:30
And we know that the separation between the two lenses, the distance between them, is 17 centimeters.
00:39
Now, we want to know how far behind that first lens are we going to get our image formed.
00:49
So we have our object here, we have our focal points, focal lengths, and we want to know how far away are we going to form this object here.
01:05
Q1, this length, how long is that? over here we have p1.
01:09
We can use the thin lens formula, which is 1 over f equals 1 over p plus 1 over q to solve for that.
01:19
If we rearrange it, we get that q1 equals 1 over f1 minus 1 over p1 to the negative 1.
01:29
So everything is going to be 1 over the stuff in that brackets.
01:32
And if you plug in the values you have, you get that q1 is 12 centimeters.
01:40
So this is 12 centimeters away.
01:43
Now how much further until we hit that second diverging lens? well, s is 17 centimeters, so s minus q1 minus 12, will give us 5 centimeters, which is also the distance from our new object or our real image produced by our first lens to our second lens.
02:04
So that's going to be p2.
02:08
This happens to be the focal length of our second lens.
02:13
But regardless, we now have a real image that's going to be going through a diverging lens.
02:22
So all of the libraries are going to diverge from here, and we're going to have only a virtual image.
02:29
So we can't put a screen down and view that image.
02:33
So the only real image in this problem right now is that first one...