answer these questions using this simulation: http://physics.bu.edu/ulab/prelabs

Question

answer these questions using this simulation:

http://physics.bu.edu/ulab/prelabs/prelab_geo_optics_1new.html

1. Place the object closer to the converging lens than the focal point is. Describe the image characteristics. What happens to the image when the object is moved even closer to the lens?

2. Now change to a diverging (concave) lens. Describe the image characteristics for this case. What happens to the image when the object is moved closer to the lens?

3. Lenses have two focal points, one on each side of the lens. If an object is placed at the focal point to the left of a diverging lens, where is the image? Compare this to what happens when the object is placed at the focal point to the left of a converging lens. Comment on what you observe.

4. Look carefully at the ray diagrams shown in the simulation. In the simulation, a light ray passing through a lens changes direction once, when the ray reaches the vertical line passing through the middle of a lens. Where does the change of direction happen for a real lens? How many changes in direction occur for a light ray passing through a real lens?

Explanation / Answer

1) object is placed between focal point and lens, the image si formed in the same side as object.

image distance is greate than object distance.

The image is virtual,upright and larger in size than object.

As the object is moved closer to the lens, the image distance increases and the size of the image also increases.

2)

For a diverging lens the image is always formed between the object and the lens.

so, the image is virtual,upright and smaller in size than object.

As the object is moved closer, the image distance decreases and size of the image also decreases.

3) if u = f,

use, 1/u + 1/v = 1/(-f)

1/v = 1/(-f) - 1/f

v = -f/2

so, image is fomred at -f/2

negative sign represents the image is virtual.

for a conerging lens,

u = f

1/v = 1/f - 1/u

1/v = 1/f - 1/f

v = infinite

so, image is fomred at infinite distance.

4) at two places. at left curved surface and right curved surface.

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