The Measurement of the Focal Lengths - Lab Report Example

Abstract:

This paper comprises of a lab report that sets the basis for the general functionality of lenses including the measurement of the focal lengths. It studies extensive images that are formed by both single and combined lenses.  On the other hand, it gives a clear distinction between the concave and the convex lenses. This is because; convex lenses are responsible for the convergence of light, while concave lenses are responsible for divergence. So, the entire experimental set-up as well as the computation of focal lengths and all the other factors clearly shows the ultimate practicability of lenses. All these have been exemplified well in the analysis segment and discussion segment.

Introduction:

The main objective of this experiment is the determination of the focal length as well as the focal points of lenses. In this entire experiment, two methodologies for finding out the spherical lens’s focal length were chosen. They refer to the lens replacement methodology and the lens formula methodology. The first method sets the basis on the lens formula which is very essential when it comes to this concept. This formula states that there is a linear relationship between, image distance (v), object distance (u), and focal length (f) of the spherical lens (Boston, 2010). Therefore, after recording some variables regarding the object and the image distances, the computation of the focal length will be a very easy task. This can be done using the following formula:

 ; Where f is the focal length, u- is the object distance, while is the image distance.

On the other hand, the lens replacement technique has to do with a number of frameworks. For instance; if the screen and the lamp housing are separated from maybe (a) to around (s) cm, two positions between shall definitely be established, hence leading to the formation of an image on a screen. This is in accordance with the concept of reversibility of light. From that point, the focal length can hence be computed using the following formula:

       F =; Where d is the distance between the lenses.

            Figure 1: The lens formula Method

Figure 2: lens replacement method

Experimental Procedure:

The experiment started after assembling all the apparatus that included; the optical lens, light source, optical benches, lens mounts, as well as screens. Using the lens mounts, a lens was mounted on a flat surface. The targeted object was then placed at a specific distance in front of the lens. The screen was thus placed at the rear end so as to monitor the reflected image. The object distance was slightly altered, and based on this, the consequent variation in the image distance was thus determined. The same procedure was repeated with a constant variation in the object distances. The results were recorded accordingly for further analysis and discussions.

Results and Analysis:

The obtained results were recorded in the table shown below:

Trial Number

Object Distance (u)

Image Distance (v)

Focal Length (f)

1

29 cm

71cm

20.59

2

31.5 cm

58.5 cm

20.48

3

40 cm

40 cm

20

The focal lengths were computed as shown below:

                                   Therefore for trial 1

                                                               = 20.59 cm

Trial 2:

                                                                       = 20.45 cm

Trial 3:

                                                                       = 20 cm

Discussion/Conclusion:

From the above results and analysis, the focal point seems to be ranging at an average range of around 20 cm. The slight variations with regard to all three trials were mainly due to small technical errors or conditions. The experimental results also proved that the lens-displacement methodology was the most appropriate technique that can be used to attain accurate results (Boston, 2010).

On the other hand, the results show that variation in the object distance leads to a consequent variation in the image distance, while the focal point remains constant. This hence works towards determining the common applicability of lenses, whereby the focal point is often taken into dire consideration.

Generally, this experiment emerged successful in that; all the projected aims and objectives were attained. It went to the extent of exemplifying the techniques on how to compute the focal points, as well as the overall features regarding the lens’s practical sense. On the other hand, it gave a clear distinction between the concave and the convex lenses. This is because; convex lenses are responsible for the convergence of light, while concave lenses are responsible for divergence. So, the entire experimental set-up as well as the computation of focal lengths and all the other factors clearly shows the ultimate practicability of lenses.