At what distance from the lens is the image

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In summary, the conversation discusses a homework problem involving a punctual source of light in the focal point of a diverging lens and determining the distance of the image from the lens. The homework equations state that objects at the focal point do not have an image. Possible ways to draw the road of rays are discussed, including finding the image position using a formula or drawing rays for an off-axis point at the focal distance. The conversation also addresses the location of the image for an object very near the focal point in the case of a converging lens and the relationship between the object distance and focal length for a diverging lens.
  • #1
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Homework Statement


A punctual source of light is in the focal point of a diverging lens. in which distance from the lens is the image. Draw the road of rays.

Homework Equations


The objects at focal point don't have an image.

The Attempt at a Solution


http://s32.postimg.org/ociblmif9/image.png
So how should I draw the rays (it says in the problem)?
 
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  • #2
My feeling would be to find the position of the image, then draw the ray paths accordingly.

You can find the image position using a formula, or, perhaps more interestingly, by drawing rays for an off-axis point at the focal distance. (The problem with the focal point being on-axis is that all the standard rays are coincident.)
 
  • #3
annalian said:

Homework Statement


A punctual source of light is in the focal point of a diverging lens. in which distance from the lens is the image. Draw the road of rays.

Homework Equations


The objects at focal point don't have an image.
Are you sure? Where is the image if the object is very near to the focal point in case of a converging lens?
What do you know about the focal length of a diverging lens?
Where is the image if the object distance is do = |f|?
 

1. What is the formula for calculating image distance?

The formula for calculating image distance is 1/f = 1/o + 1/i, where f is the focal length of the lens, o is the object distance, and i is the image distance.

2. How does the distance of the object from the lens affect the image distance?

The distance of the object from the lens is directly proportional to the image distance. This means that as the object distance increases, the image distance also increases. Similarly, as the object distance decreases, the image distance decreases as well.

3. What is the relationship between focal length and image distance?

The focal length and image distance have an inverse relationship. This means that as the focal length increases, the image distance decreases, and vice versa.

4. Can the image distance be negative?

Yes, the image distance can be negative. A negative image distance means that the image is formed on the same side of the lens as the object. This occurs in cases of virtual images, where the light rays do not actually converge to form an image.

5. How does the type of lens affect the image distance?

The type of lens can affect the image distance by changing the focal length and the curvature of the lens. A convex lens will have a shorter focal length and a larger curvature, resulting in a shorter image distance. A concave lens, on the other hand, will have a longer focal length and a flatter curvature, resulting in a longer image distance.

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