1. You use a concave mirror to focus the light from the sun to a small point. Is
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Question
1. You use a concave mirror to focus the light from the sun to a small point. Is this point located at the focal point, further from the mirror than the focal point, or closer than the focal point? Explain.
2. A concave mirror has a focal length of 10cm. Where can you place an object so that you will see a real image? Will this image be upright or inverted? In front of the mirror or behind the mirror?
3. What will happen to the image if you block half of the mirror with a card? If you block half of the object with a card? If you remove the mirror? Explain your answers.
4. For the mirror in question 2, where can you place an object so that you will see a virtual image? Will this image be upright or inverted? In front of the mirror or behind the mirror?
5. A second concave mirror is curved more so that its radius of curvature is half as large as the radius of curvature of the mirror in question 2. What is the focal length of this mirror? Explain.
6. Can a real image be formed by a convex mirror? If yes, describe where you should place the object, and where the image will be located. If no, explain why not.
7. Can a real image be formed by a plane mirror? if yes, describe where you should place the object, and where the image will be located. If no, explain why not.
Explanation / Answer
1) The point is located at the focal point. Rays coming from infinity merge at the focal point. That's why.
2) The object can be placed anywhere except between focus and pole. i.e object must be placed more than 10 cm from the mirror. The real image is inverted and in front of the mirror.
3) When half of the mirror is blocked, half amount of light is obtained, thus intensity of image is reduced to half. When half object is covered, image of half of the object is formed as usual. when mirror is removed, there is no image.
4) For virtual image, the object must be placed between focus and pole ie within 10 cm of the mirror. The virtual image will be upright and behind the mirror.
5) f = R/2. Thus focal length of new mirror = 20 cm.
6) Real image can't be formed by a convex mirror.
7) Real image can't be formed by a plane mirror.
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