MPTL14 2009

Udine 23-27 September 2009

CCD IN YOUR POCKET Tibor Szakmány, University of Szeged; Dept. of Experimental Physics

Abstract Personal computers are fully accepted in education. Other digital gadgets are less current in schools. Mp3-, mp4-players, mobile phones and digital cameras are in every child’s pocket. These gadgets are packed full with modern technology, like CCDs, LCDs etc. Pupils have a positive attitude toward modern high-tech products. Therefore it is practical to promote them as demonstration- and experimental tools in schools. We can use them in physics education: mechanics (stroboscopic photography, time-lapse photography, measuring energy transformation, freefall, measuring speed), optics (self-diffraction, NIR-sensitivity, polarization, colour mixing). The interactive poster shows some of the developments, what we successfully integrated into the education of future physics teachers. 1. CCD in school Personal computers are fully accepted in education. Other digital gadgets are less current in schools. However, it is a fact: Mp3-, mp4-players, mobile phones and digital cameras are in every child’s pocket. Mobile phones and digital cameras use CCD image sensors. Compact digital cameras and built in cameras in mobile phones are common in these days. Most have a built-in flash, live preview, motion picture capability, macro capability, autofocus system. Compact cameras are usually designed to be easy to use. Compact cameras are also called point-and-shoot cameras. It is easy to take images, and display them on a screen in a classroom immediately after they are recorded. Higher priced cameras know more. They have advanced features like: manual control of aperture, shutter speed and focusing; faster continous shooting; better video. Some cameras can be controlled through a computer. These features make them more efficient in physics teaching and learning. It is posible to use digital cameras in schools for demonstration and even for measures. This article shows some examples of using digital cameras to learn more about motions.

2. Motions and CCD 2.1. Inertial frame of reference Compact digital cameras can help in teaching reference frames. Compact cameras are so small and light, that it is easy to put them on moving objects. This way we can show even the fictitious forces in non-inertial frames. Just put a small camera on a flat rotating surface and make a video what happens with a small ball in this non-inertial frame. 2.2. Speed of motion Digital cameras can help in stopping motions. The higher priced cameras have manually controlled shutter speed. With the right shutter speed it is posible to take picture almost any type of motion. You can take a picture of Brownian motion of flying dust in beam of sunlight. For this use slower shutter speeds, like 1s-0,6s. The gap between curtains can be used for lighting the dust, and it helps with the darker background too.

Figure 1: Brownian motion of a dust particle (0,6s)

You can catch non visibly fast events by using faster shutter speeds. Take a picture of a 60-100Hz CRT montior with 1/1000 of a second. You can catch the movement of the electron beam.

Figure 2: CRT monitor with slow refresh rate (1/1000 s)

You can make videos about slow motions like Sun and star motion, or cloud and plant movements by making time-lapse videos. Time-lapse photograpy is a technique where each frame is captured as a still image. You can take images by any frame rate if you use a program to controll the camera. Some of the digital camera makers give you this program with the camera. Use Microsoft Movie Maker to comprise the digital images into a video. This way you can make a normal speed video about slowly moving objects or slow processes (Wikipedia 2009) 2.3. Tracking movements Digital cameras usually have continous shooting and video mode. Digital video comprises a series of digital images displayed in rapid succession at a contant rate. These images are called frames. Frame rate means number of displayed images in a second. We can take a series of pictures of a moving object. We can play back it frame by frame, if we using media player or image viewer programs. Some of these programs can take images out of a video. We can piece together the parts of these frames with the help of picture drawing programs - like Microsoft Paint. This way we can get a "stroboscopic image".

Figure 3: Track of a jumping toy

You can see on figure 3 the motion blur and the stoping point in the track of movement. 2.4. Time and position coordinates We can determine the time coordinates using the frame rate or by looking at the status bar of the media player program, when you save a frame. We can determine the position in pixel coordinates, if we use a picture drawing program (Hughes 2006). Point the cursor on the moving object in Microsoft Paint, we can see the position of it in pixel coordinates on the status bar (figure 4).

Figure 4: Pixel coordinates of the cursor in Paint

The (0,0) point is in the left top corner. The left number is the horizontal coordinate, the right number is the vertical coordinate. We can collect the cordinates into Microsoft Excel and make a graphic visualisation of the track of the moving object. 2.5. Measuring velocity We can measure speed by using the coordinates. However there is an alternative way to measure speed of cars. Stand 5-10m next to a road, and make a sort video about traffic. Watch back the video and select a car you familiar with. In a class there will be always some car expert boy. When you have the choosen car, you can take out two frames of this car's movement by using Microsoft Movie Maker. Note down the time for these frames. Make one picture by mixing these two frames together with Microsoft Paint.

Figure 5: Speeding driver

Figure 5 shows an image mixed from to frames. The frame rate of the video was 15fps. There was 6 frame between the mixed two frames. Use the Internet to find the exact lenght of your choosen car. Car makers give this information out in milimeters. Measure the lenght of the car in pixels by using the pixel coordinates. Now you can find out the conversion number between milimeters and pixels by dividing the lenght in milimeters with the lenght in pixels.

Measure the displacement of the car by measuring the distance between the two car positions in pixels. Multiply the displacement by the conversion number and divide it by the time and you get the velocity of the car.

3. Further notes The ideas above are some of the developments, what we successfully integrated into the education of future physics teachers.These examples can help with theacing mechanics, and motions. But there is more: a digital camera can be useful when we talk about optics - diffraction, polarization, colour mixing, spectrums (Planinsic 2004 and Westra 2007), NIR-sensitivity (Zetie 2006) etc. Pupils like digital gadgets. If they can, they buy the newest and most modern one. Sometimes they know much more about using modern technology than adults or teachers. Therefore they have a positive attitude toward modern high-tech products. It is practical to use them as demonstration- and experimental tools. It makes the way of teaching, and the tools of knowledge transfer more accepted. The work with these gadgedts can motivate children. References Wikipedia http://en.wikipedia.org/wiki/Time-lapse , accessed 2009 september Hughes, Stephen W. (2006): Measuring the orbital period of the Moon using a digital camera, Physics Education 41144-150. Mark Tiele Westra (2007): A fresh look at light: build your on spectrometer; Science in School - Issue 4 http://www.scienceinschool.org/2007/issue4/spectrometer/ , accessed 2009 september Planinsic, Gorazd (2004): A photoshoot for food and drink: camera ‘sees’ more than you think, Physics Education 39 32-33. Zetie, Ken (2006): Cheap camera illuminates the infrared Physics Education 41208.