• Join over 1.2 million students every month
• Accelerate your learning by 29%
• Unlimited access from just £6.99 per month
Page
1. 1
1
2. 2
2
3. 3
3
4. 4
4

# 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

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.

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 %

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

# Related AS and A Level Microscopes & Lenses essays

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

4 star(s)

Results: Table 1: anomalous results highlighted; where the lowest and highest values of (v) for any one value of (u) were more than 5mm apart I circled them as anomalous results to be re-investigated to an appropriate level of precision.

2. ## To investigate the relationship between the distance between a lens and an object, and ...

Care must be taken to ensure that both the power source and the lamp are safe to use. Results: I obtained the following results from my tests: U value (cm) First run V (cm) Second run V (cm) Third run V (cm)

1. ## 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.

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. ## To investigate the relationship between u and v for a convex lens.

However using my ideal results I have found that the range between the lower values of u will have to be small and the range between the lower values of u will have to be larger. For example the lower values will have to be 18-19-21-25 and the higher values will have to be 105-125-145-170-200.

2. ## Investigating the Positioning of Real Images formed by a Convex Lens.

I will also make sure that there are no objects on the desks or floor that people could touch and possibly hurt themselves by touching or knocking.

1. ## Finding the Focal Length of a Lens.

A sharp-edged light source (e.g. a square) would have been more helpful as it would have been easier to see if the edges were in focus. * The object-lens distance must be greater than the focal length of the lens; otherwise a magnification of the object occurs.

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

Second Graph: Power result: The plotted values have produced minimum, mean, and maximum gradients that are closer together than the previous experiments. They intercept the x axis at -6.64 D, -6.70 D and -6.76 D respectively. The average of these results turns out to be 6.70 D with an uncertainty of +/- 0.04.

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