Mirror Magnifying Light

by admin on December 15th, 2006

filed under Mirrors

VINTAGE GENERAL ELECTRIC LIGHTED MAKEUP MIRROR W 4 SETTINGS FLIP MAGNIFYING
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VINTAGE 2 WAY LIGHTED MAGNIFYING MIRROR
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Optics, plz help me out!?

1). Use the equation 1/o + 1/i = 1/f to solve the problem. Object distance is o, image distance is i, and focal length is f. An image of a candle appears in sharp focus on a screen that is 62 cm from a lens whose focal length is 22 cm. How far is the candle from the lens (i.e., what is the object distance)?

2)Use the equation 1/o + 1/i = 1/f to solve the problem. Object distance is o, image distance is i, and focal length is f. A near-sighted eye sees close objects clearly at 13 cm. A corrective lens will provide normal viewing distance of 46 cm. Hence the object distance is 13 cm and the image distance is 46 cm. What is the focal length of the corrective lens?

3).Would telescopes and microscopes magnify if light had the same speed in glass as in air?
yes
no
Explain.

4).If you take a photograph of your image in a plane mirror, how many meters away should you set the focus if you are 3 meters in front of the mirror?

Using the given equation is tricky. Here the o and i distances will be taken as positive only if the image and object are on either side of the lens - as in the case of a real image formed by a convex lens. If the image is on the same side as the object, take i as negative. In this convention the focal length of a convex lens is positive and that of a concave lens is negative. Now for your problems:
1) A real image is formed (since you can catch it on a screen). So the lens is convex.
i = 62 cm
f = 22 cm
1/o = 1/22 - 1/62 = 40/(22*62)
Thus o 22*62/40 = 34.1 cm
2) Here the lens presents an object at 46 cm as if it is at 13 cm to the eye. That is
o = 46 cm
i = -13 cm ( negative because the object and the image are both in front of the eye). Therefore
1/f = 1/46 -1/13 = - 33/(46*13)
ie, f = - 46*13/33 = -6 cm approx.
The negative sign shows that it is a concave lens.
3) If the speed of light were the same in glass and air, there would be no refraction and hence no convergence or divergence. So the telescopes and microscopes cannot magnify objects.
4) In a plane mirror, the image is as far away from the mirror as the object is. The distance between the person and the image is twice the distance of the mirror from him. So you should focus for a distance of 6 m.
I suggest you ask only one or two problems in each question. Then you may get better response.