Question

1. What is a measurement? Give your own definition of what constitutes a measurement based on your previous courses with lab components (biology, chemistry, physics) 2. Two engineers must measure the distance between the McGill metro station to the athletic centre to build an underground tunnel. One engineer finds that the distance is 9134 ± 5m while the other finds that the distance is 9150 ± 20m. In what ways can they compare their measurements? Do their measurements agree? Explain. 3. The city is considering to build a metro line between McGill station and the station at University of Montreal. To do this, an engineer decides to use a km-long ruler whose smallest divider is a meter. She did not use any other measuring devices. She takes her measurements and presents her findings to her team as 3653.4500m. What is the uncertainty on this measurement? Did she present enough, too little or too many digits about her measurement? Why? 4. Two groups of researchers are trying to test their new methodology to measure the speed of light c. Current research shows that the speed of light is roughly c- 2.99792 x 10 m/s. The first group finds that c 2.88±0.02 x 108 m/s while the second group finds that c = 3.0±0.2 × 108 m/s. What do these measurements tell you about their methodology in the context of precision and accuracy? What type of mistake may have caused the discrepancy in the first group's results? 5. How do you know if an experimental result is acceptable and trustworthy? What gives you confidence that your data is trustworthy?

Answer 1

1. Measurement: Measurement is defined as the action of measuring something like length, radius, distance etc. Based on the lab experience measurement can be done in physics for distances using vernier callipers, in chemistry liquids can be measured in liters in a measuring jar.

2. Engineers generally measure the longer distances or distances between two places with a laser tape which Gives the distance between two objects placed far or between places. While measuring distance or any other thing we do not get the same readings at all the time. Some errors occurs due to the environmental changes. Therefore we cannot get the same reading every time we measure. And while doing the experimentation one should not consider only one reading at least he needs to take the average of 5 to 6 readings he records. So in the above the two engineers should take the average of both the readings in order to compare their results.

3. Uncertainty: The terms uncertainty is defined as the accuracy of a measuring device. For a example if we get the distance between two objects as 5.05+0.02m the true value is about 5.05m and the minimum to maximum distance varies between 5.03m to 5.07m. Therefore +0.02m represents the uncertainty of the device. In the above she uses a km long ruler to measure the distance and always the uncertainty is round to the same decimal place as to the experimental value. The uncertainty for the above reading measured by the engineer is 0.4500m.

4. Precision: the term precision is defined as the closeness of two or more than two measurements to each other.

Accuracy: The term accuracy is the value that matches to the standard or to the known value. In the above example which measures the speed of the light the first group shows they used a low precision instrument and so got the reading less than the actual speed of the light. The mistake is using a low precision instrument to measure the speed.

5. We can know the experimental result can be used or not by comparing the results with the standard or the true value. One cannot get the exact results at all the time while conducting the experiment. So what’s close to the standard value can be taken. And at the same time the experimental results can be accepatable if it is in the range of standard values that’s make a person to accept the results.