In this experiment one source of error that arises is the alignment of the pins. It is not possible to measure when the pins are all exactly aligned. However, it is possible to say with reasonable confidence that the pins are aligned plus or minus half a degree. The error in the pin alignment is then said to be half a degree. Once the pins are in place, other errors also arise. There is an error of half a degree in the procedure of drawing a straight line through the pins. There is also an error of half a degree in the accuracy of the angles as written on the graphical worksheets from distortions during the photocopying process. Furthermore, there will be some inaccuracy in the placement of the mirror and the acrylic rectangle and equilateral prism. Assume that this error is also half a degree. Lastly, once the rays have been drawn, it is necessary to measure their angles with a protractor. Three sorts of errors happen during this measurement. First, the protractor must be lined up properly, in order to read off the angle. The error in doing this is called the zero point error. Secondly, there is some difference between the true angle and the markings of the angle on the protractor. This is called the calibration error of the protractor. Third, there is some uncertainty in reading the angle because the angle to be measured will not land exactly on a line of the protractor scale. This is called the measuring error. It has been found in practice that for instruments with scales (such as a protractor or ruler), the measuring error is often half the smallest scale division on the instrument. For the protractors used here, the smallest scale division is one degree, so the protractor measuring error is taken to be half a degree. It is estimated that each of the other two errors, the calibration error and zero point error, are at most half of a degree.
Sources of Error:
Inherent error in protractor
error in judging the position of no- parallax.