Activity 1 - Measuring the volume of a Test Tube

1. Describe any variation in your results for volumes of the test tubes

Students should say how much variation there is, the range of values, or the maximum and minimum values

2. Suggest why there are differences in the volumes measured.

There are a few common causes of uncertainty in measurements:

• Problems related to the skill of the user - reading the lowest point of the meniscus, etc.
• Errors in the functioning of the measuring instrument - unlikely with a measuring cylinder, but a graduated pipette filler may leak.
• Properties of the substance / object being measured - the surface tension of water allows a test tube to be filled beyond the rim. It is hard to say exactly when it is full.
• The act of measuring - something in the way the measurement takes place alters the measurement - e.g. a thermometer may cool a liquid slightly, drops of water may stick to the sides of a beaker.
• Changes in the environment, e.g. temperature - may cause the liquid to expand, or evaporate

3.  What is the measuring error (the uncertainty) of each piece of equipment?  This is half the smallest graduation. 
Add this to your results table.

This depends on the equipment used in the lab

4. If you used the piece of equipment more than once to take one measurement you must multiply the error by the number of times it was used.

Add this to your results table

If a small measuring cylinder 20 ml is used three times to find the volume of a beaker of water 50 ml and the uncertainty is +/-1ml each time, then the total uncertainty will be +/-3ml

5. Which piece of equipment gives the most accurate answer?

This depends on the equipment used in the lab

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Activity 2 - Measuring Mass of Rice Grains

See the table above for overall uncertainties.
The balance is has an uncertainty of +/- 0.01g
(unless the manufacturer says otherwise, some small jewelry balances claim  +/- 0.01g but in reality they are not this accurate.)