Make certain that the sliding weights sit firmly in the notches. Measure the mass of the disk by placing it on the pan. If not, use the zero adjustment knob to zero the balance first. Make sure the balance pointer indicates zero when the pan is empty and all three sliding weights are at their leftmost positions. In this exercise you will measure the mass of the disk using a triple-beam balance, shown in Figure 5.įigure 5 1. PHYS101 - 1 Measurement with Triple-beam Balance It is the standard practice to report the smallest measurement from a digital device as its reading uncertainty. Estimate the uncertainty in your measurements. Measure the height of the disk using the caliper. Measure the diameter of the disk as shown in Figure 4. Make sure to zero the caliper when it is completely closed, and to use mm scale. In this exercise you will measure the diameter and height of the disk using a digital caliper. PHYS101 - 1 Measurements with Digital Caliper Measure the diameter and height of the given disk using a ruler. Note also that in the previous case, where the scale division was as large as 1 cm, you were able to estimate to the nearest one tenth of the space between scale divisions whereas with 1 mm scale division you were able to estimate only to the half of the space between scale divisions. Note that the uncertainty of the measurements is now 0.05 cm with the more sensitive ruler. For very small scale divisions judged with our eyes, it is reasonable to take half of the smallest division as the uncertainty of the measurement. On the other hand, if the ruler has marks every millimeter, and the calculator falls between the 144th and 145th marks as shown in Figure 2, you may record its length as 14.45 ± 0.05 cm. Note that the doubt is in the last digit recorded. The value 0.1 cm is said to be the uncertainty of this measurement from this ruler. It means that your measurement is between © KFUPM – PHYSICS revised ġ4.3 and 14.5 cm. The best you can do probably is to record it as 14.4 ± 0.1 cm.
This estimation introduces the uncertainty in the measurements.įigure 1 You may now estimate the length of the calculator as 14.3 or 14.4 or even 14.5 cm. This is done by estimating the measurement to the nearest one tenth of the space between scale divisions. To get a better idea of how long the calculator actually is, you will have to read between the scale division marks. For example, if a ruler has marks every centimeter, and a calculator falls between the fourteenth and fifteenth marks as shown in Figure 1, you can be certain that the calculator is longer than 14 cm and less than 15 cm. Uncertainty All measurements are approximations no measuring device can give perfect measurements without experimental uncertainty. Significant Figures Objectives To understand the concept of significant figures and to learn how it relates to measurements in physics lab.
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