• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

Find the focal length of a given convex lens.

Extracts from this document...

Introduction

Experiment no. 9                                                            

Aim: -

To find the focal length of a given convex lens.

Apparatus: -

        Convex lens                                           Metre rule

        Screen                                           Candle

            Matches                                   Wooden blocks        

Theory:-

In this experiment the focal length of a lens is found out. The focal lens of a lens is the distance from the principal focus to the optical centre. It is the point where the image comes into focus when seen though the lens. The focal length of a lens depends on the curvature of each surface. So the more highly curved the surface, the shorter is the focal length and visa-versa. In this experiment the lens is first placed at L1, between the screen and the illuminated object. When the illuminated object comes in focus on the screen the distance of L1

...read more.

Middle

The independent variable is the distance d, the distance between the screen and the illuminated object.

The controlled variable is the intensity of the illuminated object and the focal length of the lens

Procedure

  1. Place the illuminated object at a distance of 50 cm from the screen and set up the apparatus as shown in the figure above.
  2. Now place the lens somewhere close to the screen and see in which position of the lens does the illuminated object comes into focus on the screen.
  3. Mark this position as L1 and record its distance from the illuminated object.
  4. Now place the lens somewhere close to the illuminated object where the object comes into focus on the screen.
  5. Mark this position as L2 and record its distance from the illuminated object.
...read more.

Conclusion

Object and image distances should be measured along a line parallel to the principal axis.The illuminated object should be placed in the region of the optical centre.Check the focal length of the lens using the distant object method to ensure that the object distances used would be suitable.

Evaluation

The focal length of the lens is found out to be 10 cm which is very accurate to the actual value. Therefore the hypothesis stated in the beginning is proven to be correct and the focal length of the lens is found out. The actual value told is 10.4 cm so the absolute error and percentage error can be found out: -

Absolute error:

Absolute error = actual result – observed result

                        = 10.4 – 10.0

                        = 0.4

Relative error:

Relative error =

                       =  

                      = 0.0385

Percentage error:

Percentage error = relative error × 100

                           = 0.0385 × 100

                           = 3.85 %

...read more.

This student written piece of work is one of many that can be found in our AS and A Level Microscopes & Lenses section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related AS and A Level Microscopes & Lenses essays

  1. Peer reviewed

    Physics coursework; Finding the focal length of a lens using a graphical method.

    4 star(s)

    the experiment 3 times, once I have done this I will re-do any anomalous results and finally; take an average value for (v) for each of the 8 measurements of (u). ==> The measurements will be done using a ruler which is correct to the nearest mm; I feel this

  2. To Determine the Focal Length of a Convex Lens.

    0.034 65 28.40 0.015 0.035 70 27.20 0.014 0.037 Conclusion: I have come to the conclusion that the further that the length from the object to the optical lens (U) the less the distance from the lens to the screen (V).

  1. Does the focal length of a lens depend on the colour of light used?

    may have to put the ray box or screen on top of a book to ensure this). I have worked out appropriate object distances so that when I am plotting my graph the points are evenly spaced. This means that I will be able to see the correlation of the points on my graph more easily.

  2. In this experiment I will be investigating the efficiency of a motor. I hope ...

    the sensitivity of my practical when measuring and recording: To measure the lengths of object distance (u) and image distance (v), I will be using a metre rule and slowly increasing the lengths of both. The error in reading from a metre ruler in each reading is +/-0.5mm therefore the error in accuracy is +/-1mm.

  1. My experiments focus is to obtain an accurate measurement for a specific lenss power.

    Reliability: The uncertainties in general are smaller than previous experiments. The highest uncertainty of the third experiment is 0.0686 D, whilst the second experiment's is 0.091 D and the first experiment's is 0.0873 D. The uncertainty is only +/- 0.04 Dioptres in the power result.

  2. Lenses experiment

    the only thing as part of the experiment that I will be changing. Method To find out which lens I want to use I will have to find out the focal lengths of them, because I want the one with the most easy to work with and of a reasonable size.

  1. The focal length of a convex lens.

    They are related by the lens formula: 1/f = 1/u + 1/v ...... (1), all the quantities being positive. A plot of 1/v against 1/u will give a straight line that has a slope of -1 as shown in Fig.

  2. Finding the Focal Length of a Lens.

    As Activity 23 is the basis of this investigation, it's a good idea to follow what it asks. However, before I conduct the experiment, I will pre-test Activity 23 to see if there are any possible problems. Activity 23 suggests that we use a coloured light source and a lens with which we can focus the light onto a screen.

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work