Experiment 7 Lenses

Purpose：

the purpose of this lab is to measure the focus of the lens, find the relationship between object distance and image distance, and the relationship between object height and image height, also calculate M. then by view the direction of the image to determine the type of image.


Equation:

Obtics bench, Light, Object(must be a shape that is different on top and bottom), Object holder, Lens and lens holder, Viewing screen card, viewing screen holder.




Experiment and Data Collection:

before this experiment, we already know the focus point of the len we are used, then, set up the equipment, fix the len with a object holder in the middle, and on one side put the light source and object, on another side of the len put a white board to obtain the image. between the len and light source, the len and white board, we all put a meter to measure the distance. first of all we set up the object distance equal to 5 focus point, then, we move the white board on the other side of the len to fix it when we get a clear image. then we change to 4 focus point, and so on. we get the data below:

Object distance do /cm	Image distance di /cm	Object height ho /cm	Image height hi /cm	M	Type of image
5f = 70	22.5	3	1	-9/28	Inverted
4f =56	24.0	3	1.5	-12/23	Inverted
3f = 42	28	3	2.1	-2/3	Inverted
2f = 28	43	3	4.8	-43/28	Inverted
1.5f = 21	85	3	12.5	-85/21	Inverted

Change the object distance to 0.5 f. what happens to the image: we can not see the image for fact, we can see wirtual image, because the object distance is less than 0.5 f. take the card away and look throught the lens at the object to view the image. the images is upright.

Plot a graph of image distance, di vs object distance, do using centimeters, the shape of this graph should indicate an inverse relationship.



plot a graph of inverse image distance vs negative inverse object distance, the graph is below:

find the regression line or best-fit line for the data and record the slope and y-intercepts. we get from my graph, slope = 0.99 which is represent close to 1, and y-intercept represent the 1/f.

using the regression line from your graph and substituting in the axis values, write the equation that relats di and do.

we get equation: -1/do+1/di=1/f.

Conclustion: we get the conclustion from the experiment is, the image distance di is increase by the object distance do decrease. when the object distance is less than one focus point, the image height hi is increase by the objet distance do decrease. and for the object distance do is greater than the one focus point, all the image we get is real on the other side of the len, and all the real image are invert compare the real object. if the object distance do is less than the one focus point,
we will not get a real image in the other side of len, what we get is virual image, and the image is upright. by plot a graph of inverse image distance vs negative inverse object distance, we get a liear graph, then get get a relationship between object distance, image distance and focus : -1/do +1/di = 1/f.