Experiment 10: lenses

Objective: The purpose of this experiment is to study the properties of lenses. Student will be provided with a converging lens; they need to adjust the distance between the light source and the lens and study the images formed by the lenses at different distance. The focal length of the lens is determined by placing an object in an infinite position, the point where the image formed is the focal point. The object this time can be a sun. The focal length of the lens is determined to be 15.5cm. Then, students has to put the object, the V shaped filament, in specific position as required by the lab manual; they have to find the sharp image and record the observation.

 Figure 1: The image formed is inverted.


Figure 2: light from the object passes through the lens.

Materials:

Socket lamp with V-shaped filament

Large converging lens

Large split lens or masking tape

Lens holder for large lens

cardboard

Meter stick

Data and Analysis

Focal length (f) = 15.5 ± 0. 5 cm

Table 1: Recorded data of the object and image distances and heights

Object distance as a multiple of f(cm)	Object distance(cm)	Image distance(cm)	Object height(cm)	Image height(cm)	M	Type of image
5f	77.5 ± 0.5	28.70 ± 0.5	8.50 ± 0.2	3. 0 ± 0.5	0.35	Diminished, Inverted, real
4f	62.0.0 ± 1.00	28.5 ± 0.5		4.20 ± 0.2	0.494	Diminished, Inverted, real
3f	46.5 ± 0. 5	34 ± 0.5		6.40 ± 0.5	0.75	Diminished, Inverted, real
2f	31.0 ± 0.20	51.70 ± 0.2		14.50 ± 1	1.71	Same size, Inverted, real
1.5f	23.0 ± 0.5	96 ± 2		38.2 ± 2	4.49	Magnified, Inverted, real

Conclusion:

In this experiment, only converging lens, convex lens is used. From the experiment, student can conclude that the image formed by convex lens when the object is placed after the focal point is always inverted and real. When the object is placed further than 2F, the image formed is diminished. When the object is placed at the 2F, the image formed has the same size as object. When the object is placed before the 2F, the image formed is magnified. Since the convex lens is known as converging lens, the light ray drew on the ray diagram should be converge to a point. To determine the focal point, an object from infinite point is chosen. The rays from the infinite object come parallel and form an image at the focal point. When part of the lens is covered with tape, the whole image can still be seen, but it is much dimmer. This shows that an image can still be formed even though the light intensity is much lower. Light ray can pass through only part of the lens to form an image. When the object is placed at 0.5F, the image formed becomes virtual, magnified, and erect. It can only be seen inside the lens but not on the white board because the image is formed on the object side instead of the opposite side of the lens. This is same with concave lens, which the image is virtual, diminished, and erect. The image is formed on the object side too and cannot be seen on the white board.