To find the best position of a lens to give the best magnification Essays

To find the best position of a lens to give the best magnification Essays To find the best position of a lens to give the best magnification Essay To find the best position of a lens to give the best magnification Essay Aim To find the best position of a lens to give the best magnification. Theory There are two basic types of lenses, convex lenses and concave lenses. A convex lens is also called a converging lens and a concave lenis is also called a diverging lens. Convex lenses are thicker in the middle than at the edges and concave are thinner in the middle than at the edges, which is exactly the opposite. The diagram below shows some examples of both types of lenses. Diagram 1 If a beam of light is directed parallel at a convex lens then the light is brought to focus by the lens. If the beam of light is directed along the lens axis (the line through the centre of each surface), the rays are brought to a focus on the axis at the focal point of the lens. The focal length (f) of a convex lens is the distance from the lens to the point where the rays are brought to a focus. Diagram 2 If a beam of light is directed parallel at a concave lens then the light rays are made to diverge from the lens. The focal length (f) of a concave lens is the distance from the lens to the point where the rays appear to diverge from. Diagram 3 Ray diagrams are used for showing how images are formed and predicting where the image will be formed. For simplicity, rays are shown bending at the line through the middle of the lens. In reality, bending takes place at each surface. Examples are shown below. Lenses are made up of a large number of small-angle prisms. Keep all the previous information in mind, at distance h from the optical centre P of a lens, (see diagram below). If a paraxial ray (a ray that is close to the axis that is making small angles with it) parallel to the axis changes angle when heating the lens there is always going to be a small deviation (D) after. Since the lens is small angled and is refracted trough the principal focus then the tangent of a small angle equals the small angle in radians, D=h FP Diagram 4 Now look at the diagram on the next page. If a paraxial ray from O is incident on the lens at distance h from the axis, it must also suffer deviation (D). Since all rays suffer the same amount of deviation. In the triangle IOM, the exterior angle of a triangle equals the sum of the interior opposite angles. Converging Diverging D=?+? D=?-? D=h h D=h h OP IP IP OP Therefore FP OP IP FP IP OP The above formula explains how we get; 1 1 1 where u=object distance v u f f=image distance v=focal length Diagram 5 Magnification is defined as: magnification (m) = image height object height and image height image distance object height object distance magnification = v u=object distance from lens. u v=image distance from lens Prediction From all my preliminary work, which was done on an applet at school, I predict that as the object moves towards the lens, the image becomes farther away (from the lens) therefore the magnification will increase. Variables In my experiment there are three key variables, which are: Object distance, which is the independent variable. Control variables are the variables that are changed. I will change the object distance of the lens. Image distance, which is the dependent variable. The dependent variable is the data collected, so in this experiment it will be the image distance. Focal length, which is the control variable. Control variables are the factors, which help to keep the experiment a fair test. In this experiment the control variable is the focal length. Safety Precautions To protect myself from any danger a few tasks have to be done. * Be careful with the power pack the ray box is connected with. * Do not hold the light bulb since it gets very hot. * Do not shine the light in your eyes or anyone elses. * Do not break your lens. Fair Test To make sure the experiment is fair a few factors have to be taken into consideration. To make it a fair test then I will use the same ray box, same metre ruler, same slide, same lens and the same screen. To make the experiment accurate and to prevent anomalies I will repeat the whole experiment at least three times and take an average reading. Equipment Lens Screen Ray box Slide Metre Ruler Method 1. Set up the diagram as shown below. 2. Move the object closer to the lens and measure the image distance as well as the object distance. 3. Calculate the magnification. 4. Repeat step 2 several times and repeat the experiment three more times and take an average reading. Diagram Preliminary work My preliminary work was done using a java applet that can be found on the following website:http://members.nbci.com/-XMCM/surendranath/Applet.html. My results are shown below. OBJECT DISTANCE (mm) IMAGE DISTANCE (mm) MAGNIFICATION (mm) 200 200 1 180 225 1.25 160 266.7 1.7 140 350 2.5 120 600 5 100 10100 101 80 -400 -5 60 -150 -2.5 Actual Experiment results. OBJECT DISTANCE (Cm) IMAGE DISTANCE (Cm) MAGNIFICATION (Cm) 10 Infinity (INF) Infinity (INF) 15 Infinity (INF) Infinity (INF) 16 200 12.5 18 118 6.5 20 65 3.25 22 53 2.409 24 41 1.7083 25 40 1.6 26 37 1.42 28 33 1.179 30 30 1 45 22 0.48 45 22.5 0.5 Measurements have been converted to metres. U 1/u (1/u) 2 V 1/v (1/v) 2 1/u?1/v 0.16 6.25 39.063 2 0.5 0.25 3.125 0.18 5.5556 30.864 1.18 0.8475 0.7182 4.7081 0.2 5 25 0.65 1.5385 2.3669 7.6923 0.22 4.5455 20.661 0.53 1.8868 3.56 8.5763 0.24 4.1667 17.361 0.41 2.439 5.9488 10.163 0.25 4 16 0.4 2.5 6.25 10 0.26 3.8462 14.793 0.37 2.7027 7.3046 10.395 0.28 3.5714 12.755 0.33 3.0303 9.1827 10.823 0.3 3.3333 11.111 0.3 3.3333 11.111 11.111 0.45 2.2222 4.9383 0.22 4.5455 20.661 10.101 42.491 192.55 23.324 67.353 86.694 U is the object distance independent variable. V is the image distance dependent variable. Plot (1/u) along the x-axis. Plot (1/v) along the y-axis. Graph See graph paper. Ex = E 1/u = 42.491 Ey = E 1/v = 23.324 Ex2 = E (1/u) 2 = 192.55 Ey2 = E (1/v) 2 = 67.353 Exy = E (1/u?1/v) = 86.694 x =Ex/n =42.491/10 =4.2491 y = Ey/n = 23.324/10 = 2.3324 Sxx =Ex2 nx2 =192.55-10?4.24912 =12.0015 Syy = Ey2 ny2 =67.353-10?2.33242 =12.9510 Sxy = Exy-nxy =86.694-10?4.2491?2.3324 =-12.4120 Least Squares Fitting Gradient = ? =Sxy/Sxx =-12.4120/12.0015 =-1.0342 Formula for line of best fit. (y-y) = ?(x-x) y=?x+y-?x Intercept =y-?x =2.3324-(-1.0342?4.2491) =6.7268 Therefore, y=-1.0342x + 6.7268 Since y=1/v x=1/u 1/v= -1. 0342/u + 6.7268 1/f = 6.7248 f = 0.14865m Analysis The first two points are left out, as it was impossible to accurately locate the image. I will do a least squares analysis on the remaining points. The object distance against magnification graph forms a curve. This curve represents exactly what I had predicted that the nearer the object is to the lens the better the magnification. The graph that shows the relationship between 1/u and 1/v shows a negative correlation of points and this means that as the object distance decreases the image distance increases. I had one difficulty when doing the experiment and that was the judgment in measuring the distance from the lens to the image (1 cm error) and from the object to the lens (0.5 cm error). Theoretically the best magnification should be when the object distance is nearest to the lens but before the focal point. This is represented in the experimental results above. Evaluation I think my plan worked out because I got the results I expected to get. My results for my experiment are quite accurate and reliable but there is a marginal error. My experiment could be improved if I used a tape measure instead of a ruler because there was a marginal error in measuring the object distance and image distance. The first two points were anomalous. I think that if I did the experiment again I could change the focal length.

Definition of a Chemical Period - Chemistry Glossary

Definition of a Chemical Period - Chemistry Glossary In chemistry, the term period refers to a horizontal row of the periodic table. Elements in the same period all have the same highest unexcited electron energy level or same ground state energy level. In other words, each atom has the same number of electron shells. As you more down the periodic table, there are more elements per element period because the number of electrons allowed per energy sublevel increases. The seven periods of the periodic table contain naturally-occurring elements. All elements in period 7 are radioactive. Period 8 consists solely of yet-to-be-discovered synthetic elements. Period 8 is not found on the typical periodic table, but does show up on extended periodic tables. Significance of Periods on Periodic Table Element groups and periods organize the elements of the periodic table according to periodic law. This structure categorizes elements according to their similar chemical and physical properties. As you move across a period, an atom of each element gains an electron and displays less metallic character than the element before it. So, elements within a period on the left side of the table are highly reactive and metallic, while elements on the right side are highly reactive and nonmetallic until you reach the final group. The halogens are nonmetallic and not reactive. The s-block and p-block elements within the same period tend to have different properties. However, d-block elements within a period are more similar to each other.