Help With Physics Assignment on Mirrors/Lenses

  • Thread starter wakefreak90
  • Start date
In summary, the conversation is about someone seeking help with three questions related to mirrors and lenses for a Physics assignment. The questions involve calculating the magnification of an image using a small concave mirror, determining the location and size of an image formed by a concave mirror, and finding the image of an object in a convex mirror. The conversation ends with the person asking for guidance on which formula to use for the first question.
  • #1
wakefreak90
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Please Help! Mirrors/lenses

I have been working on a Physics assignment for a long time now, and I can't seem to figure out three questions. It's due tonight, so any help would be greatly appreciated!

Here they are:

1. A dentist uses a small mirror of radius 36 mm to locate a cavity in a patient's tooth. If the mirror is concave and is held 13 mm from the tooth, what is the magnification of the image?

2. The sun falls on a concave mirror and forms an image 4.3 cm from the mirror. If an object 24 mm high is placed 13.4 cm from the mirror, where will its image be formed?

(a) Use the lens/mirror equation. Where will the image be formed?
2wrong check mark cm (from the mirror)
(b) How high is the image?

3. Shiny lawn spheres placed on pedestals are convex mirrors. One such sphere has a diameter of 45.0 cm. A 12 cm robin sits in a tree 1.2 m from the sphere. Where is the image of the robin?
(a)______ cm (from the mirror)
How long is the image?
(b)_____ cm
 
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  • #2
Hi wakefreak90! :wink:

Show us what you've tried, and where you're stuck, and then we'll know how to help! :smile:

Start with 1 … what formula do you think is appropriate?
 
  • #3


1. To find the magnification of the image, we can use the equation m = -di/do, where m is the magnification, di is the image distance, and do is the object distance. In this case, di = 13 mm and do = 36 mm (since the mirror has a radius of 36 mm). Plugging in these values, we get m = -13/36 = -0.36. This means that the image is inverted and 0.36 times the size of the object.

2. (a) Using the lens/mirror equation, we can find the image distance by rearranging the equation 1/do + 1/di = 1/f, where f is the focal length of the mirror. We know that f = 2R, where R is the radius of curvature of the mirror. In this case, R = 4.3 cm (since the image is formed 4.3 cm from the mirror). Plugging in these values, we get 1/do + 1/4.3 = 1/8.6, which gives us do = 6.9 cm. This means that the image is formed 6.9 cm from the mirror.

(b) To find the height of the image, we can use the equation hi/ho = -di/do, where hi is the image height and ho is the object height. In this case, ho = 24 mm and di = 6.9 cm (from part (a)). Plugging in these values, we get hi = -6.9/8.6 * 24 = -19.3 mm. This means that the image is 19.3 mm below the mirror and is inverted.

3. (a) To find the image distance, we can use the same equation as in part 2, but this time we need to use the radius of curvature of the sphere, which is half the diameter. So, R = 22.5 cm. Plugging in these values, we get 1/do + 1/1.2 = 1/22.5, which gives us do = 1.15 m. This means that the image of the robin is formed 1.15 m from the mirror.

(b) To find the image height, we can use the same equation as in part 2, but this time we need to use the ratio of image
 

1. What is the difference between a mirror and a lens?

A mirror is a smooth, highly polished surface that reflects light rays in a predictable way, whereas a lens is a piece of transparent material that refracts (bends) light rays in order to focus them.

2. How do mirrors and lenses work to create images?

Mirrors create images by reflecting light rays, either in a straight path (plane mirrors) or in a curved path (concave or convex mirrors). Lenses create images by refracting light rays, either converging them at a focal point (convex lenses) or spreading them out (concave lenses).

3. What is the difference between a convex and a concave mirror/lens?

A convex mirror or lens curves outward, causing light rays to diverge (spread out). This results in images that are smaller and upright. On the other hand, a concave mirror or lens curves inward, causing light rays to converge (come together). This results in images that can be either larger or smaller, depending on the distance of the object from the mirror or lens.

4. How do you calculate the magnification of an image formed by a mirror or lens?

The magnification of an image formed by a mirror or lens can be calculated by dividing the height of the image (hi) by the height of the object (ho). This can be represented by the equation: M = hi/ho. A positive value for M indicates an upright image, while a negative value indicates an inverted image.

5. Can you use the same equations for mirrors and lenses?

No, the equations for mirrors and lenses are slightly different. For mirrors, the focal length (f) is equal to half the radius of curvature (r), so the equation used is: 1/f = 1/do + 1/di, where do is the distance of the object from the mirror and di is the distance of the image from the mirror. For lenses, the equation used is: 1/f = 1/do + 1/di, where do is the distance of the object from the lens and di is the distance of the image from the lens.

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