Creating a Physical Units question

For effective learning of physical units it can be beneficial to ask students to not only input the outcome of a calculation, but also the physical unit itself. This is currently supported in the platform as a Unit question type.

With this question type it is possible to ask questions such as the one below, and provide students with rich feedback based on common mistakes that are made. In this article we explain all about how to create exercises like this one:

As a first step we will create a new exercise and select the Unit question type. We type in the description, question, and the expected answer:

The answer field of a unit question will recognize that the answer consists of two parts:

The answer field recognizes a wide range of standard units. You can find the complete overview in this help article.

After saving the question you can go to the preview page and play around with different answers. By default, the given answer will be checked using the 'an Equivalent value and unit as' check. This check verifies that the given expression has the same value and quantity. It does not check the precision.

This means that in this case the answer 1 * 10^1 N is considered to be correct, as well as the answers 0.01 kN , 1 * 10^1 kg * m/s^2 and 10 N.

If you don't want the answer 10 N to be marked a correct answer because the precision is incorrect, you should use the stricter check method: an Equivalent value, unit and precision as. An example of this is given in this section.

To make rich feedback possible the platform offers several different answer checking algorithms. The following check methods are available:

Please see the detailed help articles for the exact details of each algorithm.

If you want to check for precision you can use the an Equivalent value, unit and precision as check. This can be done by selecting this method in the answer rule modal:

One of the common mistakes a student might make in this situation is to supply 10 N as an answer.

This answer will be considered incorrect because this answer has a precision of 2, while the answer model defines a precision of 1. To give specific feedback on this case you can add a specific answer rule for the situation in which the student gave the correct value and quantity, but was not explicit about the precision:

Which results in the following feedback when giving the answer 10 N:

The precision of an expression is based on the number significant figures in the value of a unit expression. To determine the number of significant figures we use the following rules (following wikipedia):

The last case which remains are trailing zeros in an integer. These zero's may or may not be significant, which depends on the measurement or reporting resolution. Within the platform, these trailing zeros are considered to be significant.

Note that a student also can enter a calculation (such as 2+3) instead of a single number. Given that there is no generic way to handle these cases the platform considers the precision for these cases to be undefined. In the evaluation of rules an undefined precision will never be equal to a given precision.

The following table shows some examples of digits and their precision:

If you have any questions, remarks, or comments about the way the multiple select question works please let us know. Either contact us via the chat button below or sent us an e-mail via support@grasple.com