Investigating How the Size of a Shadow Depends on the Angle at Which the Light Hits the Object
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Introduction ============ The aim of the project is to see which factors affect the size of a shadow and then to look more closely at one of the factors to see how exactly it varies the size of a shadow. Variables that may affect the size of the shadow ================================================ Although, I will investigate how one factor affects the size of a shadow, there are other factors that could be investigated. Here are some examples: 1) The distance between the light and the object From the ray diagrams I can see that as the distance from the object to the light source is doubled, the length of the shadow decreases. A distance of 4cm produces a shadow of approximately 1.6cm. Decreasing the distance to 2cm(half the distance), the shadow size increases by one and a half times to produce a shadow of 2.3 cm. The three ray diagrams together show the increase of the distance between the object and light source, decreasing the length of the shadow. 2) The distance between the object and the screen The results from this are opposite varying the previous factor. In this case the length of the shadow increased as the distance from the edge of the object to the screen increased. I expected that as the distance dubled, the length of the shadow would double but according to the ray diagram that was not the case. The length of the shadow The results from this are opposite to varying the previous factor. In this case, the length of the shadow increased as the distance from the edge of the object to the screen increased. I expected that as the distance doubled, the length of the shadow would double but according to the ray diagrams, that was not the case. The length of the shadow increased by 1.6 times between changing the distance from 2 cm to 4 cm (ie:doubling the distance). How to Cite this Page
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For changing the distance to 6 cm
increased the length of the shadow, which was expected, but I was surprised as it increased by more than I had expected. When the distance was 2cm the length of the shadow was 1.1 cm. By tripling the distance to 6cm,if I then tripled the length of shadow it would come to 3.3cm.This was shown in the 3rd raydiagram as 3.3cm 3) The light source 'If the point source of light is replaced by a spreadout or extended source such as a table lamp, the edge of the shadow becomes fuzzy and indistinct. Around the area of full shadow, there is a region of part shadow where only some of the light from the lamp has been stopped' (Quoted from 'Explaining Physics' from Stephen Pople') 4) The shape of the object For this I would keep the area the same but change the shape in order to keep the same object size. I will use a rectangle and a square. From these diagrams I can clearly see that there is an effect. The rectangle has a shadow just under two and a half times larger than the squared shape's shadow. The vertical height of the rectangle is 2cm and is 1cm for the square. I think this could be a reason for the shadow length being bigger for the rectangle. 5) The angle at which the screen is This shows that by increasing the angle the screen is held at, increases the length of the shadow. As I have not measured the angles I cannot compare the increase of angle to the length of shadow in numerical form, but this could be further investigated. 6) The size of the object This is an obvious effect but it still is a factor as it affects the size of the shadow in a directly proportional way i.e.: the bigger the object, the larger the size of shadow. 7) The angle at which light hits the object This shows by increasing or decreasing the angle the length of the shadow increases. By increasing the angle to 20º the length of shadow changes from 1.9cm to 2.6 i.e.: it increases by 1.3 times. I have decided to investigate how varying the angle at which light hits the object affects the size of a shadow. It is important that all the other factors are kept constant in all my experiments; otherwise I would not be finding the effect of the factors, but of a mixture of factors. Therefore these factors will be kept constant. · The distance between the light and the object: I will keep this constant by moving the light in a semicircle, where the distance between the light and the object will stay the same. · The distance between the object and screen: The screen and the object will not be moved throughout all the experiments. · The light source · The shape of the object: The same object will be used each time. · The angle at which the screen is: The screen will be clamped 90º to the ground and will not he altered. · The size of the object: The same object will be used each time. Prediction ========== I predict that when the object is hit with light travelling 0º to the object (as shown below),a shadow will form, which will be smaller than the shadow formed by light hitting the object at another angle. As the angles get further away from the 0, the size of the shadow will increase. I think this due to the ray diagram drawn below. I also think that as the angle triples the size of the shadow will double. From information from the four ray diagrams I can draw up this very simple table which gives approximate values. Angle (º) Length of shadow (cm) 0 1.4 15 1.6 30 2.0 45 2.6 Decreasing the angle has an inverse effect on the length of the shadow. The difference between the length of shadow in angle 0º and 15º is only 0.2cm.Therfore in 15º the length increases by 0.2cm, but then the differences get bigger. Between 30º and 45º the difference is 0.7. Preliminary Experiment The reason for doing this was to find out what apparatus was suitable, how things would be best arranged, how results would be taken etc. I clamped a screen upright using a clamp stand. I selected a couple of different objects, which were different from each other to try them all out, and see which one I liked. I brought 12V torch bulb and a 1.5V torch bulb to try. I set up the experiment as shown below: The object between the screen and the light. From this I realised that * A 12V torch bulb would suit me better as the bright light created a darker shadow than the 5V bulb, which was very dim. A darker shadow was more vivid than the fainter shadow, therefore easier to take measurements from. * Moving the object and changing it with other objects made me realise that a 2D shade didn't stay upright very well. I decided not to opt for the scissors because as it was difficult to measure the size of the shadow.In the end I chose a 3D rectangular block. * Standing the block upright was a better than leaving it lying on its wider base as it was hard to see the edges of the shadow, when it was lying flat. Strategy ======== Apparatus list: * A large screen * A 12V torch bulb and a power supply * A rectangular block * A sheet with a large protractor drawn on it indicating the angles I will place the light at I need to change the angle by 15º each time i.e.: 15º further away from the starting line each time. I will measure the length and width of the shadow in order to work out the areas. The ruler will be marked with cm's and mm's. I will measure to the nearest . 
