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# Physics 104 01 Due: Thursday May 10, 2012 Spring 2012 Homework for Unit II part 1 Answer briefly but completely using complete sentences. All answers...

Text: KirkPatrick/Francis, 7thEdition.
I have seven Homework problem that are ten points each. Can you help me?

1) The light source below shines on an object and as a result a shadow of the object is produced on a screen beyond the object.

a) How should the object be moved (keeping the light and screen still) so as to make the shadow larger? Explain your answer and use a ray diagram in the explanation.

b) How should the screen be moved (keeping the light and the object still) so as to make the shadow larger? Explain your answer and use a ray diagram in the explanation.

2) A flashlight is pointed at a wall 90 cm away. A 10 cm long pen is placed at a point between the wall and the flashlight 20 cm from the flashlight.

a) How large a shadow will the pen cast on the wall?

b) Where should the pen be placed so that the size of its shadow doubles?

3) Light from a flashlight propagates in many directions. Light from a laser, on the other hand, propagates only in one direction: all the rays are parallel. Imagine you had a laser that produced a very wide beam so that you could produce , using it, a shadow of the pen from the previous question. If you varied the distance between the pen and the laser (keeping the laser the same distance from the wall), what effect (if any) would this have
on the size of the shadow? Discuss and compare/contrast the behavior in this case with what would be observed using the flashlight instead.

4) You walk into a room that has a very large window. A couch is 5 feet in front of the window. It’s dark outside and you also see a reflection of the couch when you look at the window. How far from the real couch is the image of the couch formed through reflection? Briefly explain your answer.

5) a) You stand in front of a concave mirror and an image of you is produced in front of the mirror.Is this a real or a virtual image? Briefly explain. That is, why is it real or why is it virtual?

b) Where are you standing relative to the focal point of the mirror? Explain how you know.

6) Imagine holding your finger in front of a plane mirror. Rays of light (reflections from light in the room ) emerge from each point on your finger and propagate in all directions. Imagine three of these rays emitted/reflected from a single point near the tip of your finger that go off in three different directions. All three rays reflect off the mirror.

a) Draw a ray diagram showing the reflections (reflected rays) of each of the incident rays described above. (Remember the law of reflection.)

b) An observer in front of the mirror would see the reflected light coming from a point behind the mirror (the virtual image of the point on your finger) . Modify your ray diagram in part a to show how to locate the image point using the three reflected rays. Note: This happens for each point on your finger. The image of your finger is the resultant of all these point images.

7) If an illuminated object is placed between two plane mirrors, multiple images of the object will be visible in each mirror. Each image appears further away then its predecessor. Try it. You can see the effect by holding a small mirror in front of a wall mirror. The closest of these images in each mirror, the primary image, is produced by the light that reflects directly off of the object and is incident on the mirror.

a) How are the secondary images produced? To support your answer draw a diagram
showing the path of some of the light that produces one of these images.
b) In the diagram below the object is 3 m from each mirror. How far are each of the primary images from the object?

c) How far are each of the secondary images from the object? Explain your reasoning. Hint: Where does the light that forms this secondary image appear to come from

Phy 104 - 2 - 3) Light from a flashlight propagates in many directions. Light from a laser, on the other hand, propagates only in one direction: all the rays are parallel. Imagine you had a laser that produced a very wide beam so that you could produce , using it, a shadow of the pen from the previous question. If you varied the distance between the pen and the laser (keeping the laser the same distance from the wall), what effect (if any) would this have on the size of the shadow? Discuss and compare/contrast the behavior in this case with what would be observed using the flashlight instead. 4) You walk into a room that has a very large window. A couch is 5 feet in front of the window. It’s dark outside and you also see a reflection of the couch when you look at the window. How far from the real couch is the image of the couch formed through reflection? Briefly explain your answer. 5) a) You stand in front of a concave mirror and an image of you is produced in front of the mirror.Is this a real or a virtual image? Briefly explain. That is, why is it real or why is it virtual? b) Where are you standing relative to the focal point of the mirror? Explain how you know.
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