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A concave mirror has a focal length of 38cm and a 6cm object is placed in the midpoint...

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nhl123 | Student, Grade 11 | (Level 1) Valedictorian

Posted December 17, 2012 at 8:18 PM via web

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A concave mirror has a focal length of 38cm and a 6cm object is placed in the midpoint between "f" and the mirror. What is the magnification of image?

Just to explain, first you need to find the image distance and the image height to find the magnification. The distance of the image turns out to be -38cm. The height of the image turns out to be 12cm. My question is what is the magnification of the image.

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pacorz | High School Teacher | (Level 3) Educator

Posted December 31, 2012 at 12:09 AM (Answer #1)

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We are given a 6 cm tall object placed 19 cm away from a mirror with a focal length of 38 cm. First we can find the location of the image, using the mirror formula, which shows the relationship among the focal length of the mirror and the distances of the object and the image away from the mirror:

In this example, f=38cm and Do = 38/2 or 19cm, so

1/38 = 1/19 + 1/Di

1/38 = 2/38 + 1/Di

Di = -38

Then we can use the magnification equation to calculate the magnification of the image:

In this case we know Di and Do, so we will use those:

M = -(-38)/19

M = 2

So your mirror has created an image that is 2X the size of the original object.

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