Go to the PhET website and run the geometrics optics simulation http://phet.colo

Question

Go to the PhET website and run the geometrics optics simulation

http://phet.colorado.edu/sims/geometric-optics/geometric-optics_en.html

In the questions below, select all correct answers.

In this applet you will explore lenses and focal lengths. This example is a converging lens. When you move the object, you see where the image is. If you were looking through the lens, this is where the image would appear to be focused. By default "Marginal Rays" is selected. This choice shows you the three rays we went over drawing in class.

Clicking "Virtual Image" will show you where the virtual image would be in the case that no real image is formed, however, it is not possible to move the object once you click this so you have to unclick it after you are done.

By default, the object is at a distance 2f (f=focal length) from the lens. At this point, the image is formed at a distance 2f from the lens on the opposite side and is the same size as the object.

Move the object closer to the lens (but still further than f from the lens).

1) What happens?
a)The image moves closer to the lens.

b)The image gets bigger.

c)The image moves further away from the lens.

d)The image shrinks.

e)The image moves to the other side of the lens.

f)Nothing.

2) What is the magnification of the image now?
a)m equals -1

b)m is between -1 and 0

c)m equals 1

d)m is greater than 1

e)m is less than -1

f) m is between 0 and 1

g)m equals 0

Now move the object more than 2f from the lens.

3. What happens?

Nothing.The image gets bigger.The image moves to the other side of the lens.The image shrinks.The image moves closer to the lens.The image moves further away from the lens.

4. What is the magnification of the image now?

m is between 0 and 1. m is between -1 and 0. m equals -1. m is greater than 1. m equals 0. m equals 1. m is less than -1

Now move the object so that it sits exactly at the focal length.

5. What happens?

The image moves closer to the lense.There is no image.The rays leaving the lens all come out parallel to each other.The image moves further away from the lens.The image gets bigger.The image shrinks.The image moves to the other side of the lens.Nothing.

This is one way to make a spotlight from a point source.

Now move the object so that it sits inside the focal length of the lens.

6. What happens?
The image shrinks.The image moves further away from the lens.Nothing.The rays leaving the lens all come out parallel to each other.The image moves to the other side of the lens.The image gets bigger.There is no image.The image moves closer to the lense.

Click "Virtual Image".

7. What do you see?
There is no image.The image is farther from the lens than is the object.The image is larger than the object.The image is smaller than the object.The image is on the same side of the lens as the object.The rays leaving the lens all come out parallel to each other.Nothing.The image is closer to the lens than is the object.

This is what you see when you look through a magnifying glass - the virtual image.

8. When you use a magnifying glass, where do you want the object?
Closer to the lens than the focal length. Farther from the lens than one focal length but less than two. Farther from the lens than two focal lengths

Explanation / Answer

1. b)The image gets bigger.
c)The image moves further away from the lens.

2. d)m is greater than 1

3. The image shrinks.
The image moves closer to the lens

4. m is less than -1

5. The image moves to the other side of the lens

6. The rays leaving the lens all come out parallel to each other.

7. The image is on the same side of the lens as the object

8. Closer to the lens than the focal length

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