Help with A-level physics coursework. focal lengths of lenses

In summary, the individual is in a state of panic due to having only two days to complete a physics coursework on focal lengths. They have conducted an experiment to measure the focal length of two different converging lenses and the combined focal length. However, they are unsure of how to interpret their graphs and whether the line should dip back upwards when the image distance gets close to zero. They are also unsure of how to calculate the focal lengths and the relationship between the individual and combined focal lengths. The expert suggests using the equation 1/v = 1/u + 1/f and doing some calculations with the recorded values. The expert also suggests researching the topic of lenses for further understanding.
  • #1
Xafron
hi!

im in a bit of a panic at the moment

i have 2 days to complete my physics coursework on focal lengths.

the title is:
"you are given two convergin lenses of different lengths. you are to devise an experiment:-
-to measure the focal length of each lense
-to measure the focal length of the lens combination
-to try to find any relationship between the individual focal lengths and the combined focal length."

ive got my readings and some graphs, but there is a little problem. when the graph is plotted, should the line dip back upwards when the image distance gets close to zero? if so why does it do this? if this isn't supposed to happen, and it is because of my crappy reading taking, then i think that i could be up a certain creak, without a certain paddle because i won't have the chance to re-take them...

also, from these graphs how do i calculate the focal lengths? and then the link between the combined and sepourate focal lengths?

any other useful info you think imight need for this assignment would be great too! :smile:

thanks a lot for any help!

cheers,
-Xafron
 
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  • #2
p.s. i just read the "please read before posting" thread. i don't want this coursework done for me, i just need a little help in some areas :)

sorry if i put this thread in the wrong place

cheers,
-Xafron
 
  • #3
What graphs have you plotted? That would help us..

Also have you used the equation:

1/v = 1/u + 1/f (where distances from the lens towards the object are negative and distances from the other side of the lens are positive)
 
  • #4
well, i have plotted image distance, y, against object distace, x.

the line on the first lens starts at 125cm at 100cm object distance, and then curves down to 78.5cm image dist against 30cm object. but THEN at 20cm object dist the image distance gets larger again and goes all the way up to 85cm. is that normal?

confused

i was goven the equation:

1/f = 1/v + 1/u yeah. but when getting the values for u and v do i take numbers off the best fit line on the graph or what??

cheers,
-Xafron
 
  • #5
Look at your assignment and ask yourself why you have plotted "image distance, y, against object distance, x." What did you hope it would show?

Use the equation given and do some calculations.

I would also suggest that if this assignment is important to you, perhaps you should research the topic of lenses and try to apply what you find out.
 
  • #6
thanks a lot for the help!

what graphs should i be looking at then?

and the calculations? do i just pick out some of the values for v and u that i have recorded and work with them?

really appreciate the help!

cheers,
-Xafron
 
  • #7
A graph is not always essential...

Yes, use some u and v values and get calculating. You can easily find the focal length from these values and the more you have the better result you can get by taking an average (which is in effect what you do with a 'best fit' line on a graph)
 
  • #8
thanks very much :wink:

-Xafron
 

1. What is the purpose of studying focal lengths of lenses in A-level physics coursework?

The study of focal lengths of lenses is important in A-level physics coursework because it helps students understand how lenses work and how they can be used to manipulate light. This knowledge is essential in many fields, such as optics, astronomy, and photography.

2. What is the definition of focal length?

Focal length refers to the distance between the center of a lens and its focal point, where parallel rays of light converge after passing through the lens. It is typically measured in millimeters (mm) and is an important factor in determining the magnification and clarity of an image produced by a lens.

3. How do you calculate the focal length of a lens?

The focal length of a lens can be calculated using the formula: f = (r1r2)/(r1+r2-d), where r1 and r2 are the radii of curvature of the two lens surfaces and d is the distance between the two surfaces. Alternatively, the focal length can also be measured experimentally using a light source and a screen to determine the distance at which a clear image is formed.

4. What are some common types of lenses and their focal lengths?

The most common types of lenses are concave, convex, and plano-convex lenses. Concave lenses have a negative focal length, while convex lenses have a positive focal length. The focal lengths of these lenses can vary depending on their curvature and thickness, but typically range from a few millimeters to several centimeters.

5. How does the focal length affect the properties of an image produced by a lens?

The focal length of a lens determines the size, magnification, and clarity of the image produced. A shorter focal length will result in a wider field of view and a smaller, more magnified image, while a longer focal length will result in a narrower field of view and a larger, less magnified image. Additionally, a shorter focal length may result in distortion, while a longer focal length may result in a clearer, more accurate image.

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