Convex lens
Convex lens
The lens which I can make an image for by letting you distort through convex lens … light.
A use example: Camera, microscope, telescope, magnifying glass
The point on the optical axis which goes when I exposed a convex lens to parallel light to a focus … optical axis. There is it on both sides of the lens one by one.
f refers about the distance from the center of the focus distance … convex lens to the focus. It is long as the convex lens which is thin as a thick convex lens briefly.
※Only one time of light that was the convex lens seems to be refracted, but, actually, two times of refraction happens like the chart below. However, I simplify it by the drawing figures and write only one refraction.
Drawing figures of the light
Because the position of the object is decided, a position and the size of the image of the object are fixed. Among three light to come out of a source of light like the chart below, I choose two and draw a figure to find this image by drawing figures. Of the image that a point of intersection of the light of two that went along the lens finds is located.
※Actually, innumerable light comes out of a source of light in all directions, but it is only next two of three of them to be used for drawing figures.
①After having gone along the lens, the parallel light goes along the focus to an optical axis.
②The light via the center of the lens just goes straight on. (actually, I am distorted, but hardly change with going straight)
③After having gone along the lens, the light via the focus advances parallel to an optical axis.
A real image and virtual image
The image which light gathers in the other side with the object across a real image … lens, and is done on screen. Top and bottom right and left are reverse handstand.
A use example of the real image: Camera projector, astronomical telescope
The image which there is in the side same as an object across a virtual image … lens. It is Masaki whom a direction does not turn into. The virtual image grows big than an object.
A use example of the virtual image: Magnifying glass, binoculars
Drawing figures of the image
I think about the image which is done when I put an object (candle) on the left side of the convex lens.
As the point that I showed by drawing figures of the light when I thought about an image
①After having gone along the lens, the parallel light goes along the focus to an optical axis.
②The light via the center of the lens just goes straight on. (actually, I am distorted, but hardly change with going straight)
I draw a figure in these two of them.
When an object is farther than a position 2 times as large as the focus distance
The real image is made at the position that is nearer than twice the focus distance, and the size is smaller than an object.
When there is an object at the position 2 times as large as the focus distance
The real image is made at the position 2 times as large as the focus distance, and the size is the same as an object.
When an object is nearer than a position 2 times as large as the focus distance
The real image is made at the position more far-off than twice the focus distance, and the size is bigger than an object.
When an object is nearer than a position of the focus distance
The object side has a virtual image across a convex lens, and the size is bigger than an object.
When there is an object at the position of the focus distance
The image is not done.
Way of moving of image when I moved an object
It is like the next figure when I settle the possible image and relations of the size by the place to put an object.
[about a place to put an object]
On the basis of a convex lens and
Outside … real image is made from the focus
I have inside … virtual image from a focus
The … image is not done in a focus (I have neither the real image nor the virtual image)
[about size and the position of the image]
The image works to the right when I move an object to the right, and the image works to the left when I move an object to the left.
・An object and the image work in the same direction
・The size of the image which is done when I bring an object close to the focus grows big. In addition, the size of the image which is done when I keep away an object from the focus becomes small
It is to be able to say even if this image that there are two is a virtual image. For example, the virtual image that there is grows big when I bring the object which I put towards the right in a virtual image area close to left (F). In addition, the position of the virtual image to have moves to the left.
※It is easy to be made questions, and it is difficult, but, as for the problem to ask how the size of the image and an enacted position change when they moved an object, the understanding is very all right if I learn two first of all upper point!.
[exercise]
① In the next figure, answer it whether you approach it from a convex lens, or the position of the image which is done when I moved an object to the right goes away.
② ①How does the size of the のとき image turn out?
[solution]
①When an object and the way of moving of image move an object to the right because it is the same, the done image moves to the right.
An answer. It goes away from a convex lens.
②When I approach the focus when I move an object to the right and can approach the focus, the size of the image which there is grows big.
An answer. Grow big.
I can easily untie it if I learn point! for feeling well.