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:
Setting up the exercise
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 value of the expression (in this case
10)The unit of the expression (in this case
N, interpreted asNewton)The precision of the expression (in this case
1)
The answer field recognizes a wide range of standard units. You can find the complete overview in this help article.
Default Answer Checking Algorithm
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 is equivalent unit check. This check verifies that the given expression has the same value, quantity, and 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 and 1 * 10^1 kg * m/s^2.
However, the expression 10 N will not be counted as a correct answer. The reason for this is that the precision of the answer is not correct, or in this case even non-existing. See the this section for more details.
Alternative Answer Checking Algorithm
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.
Example of rich feedback on precision
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 is not clear on the precision. 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:
How precision is determined for unit expressions
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):
Non-zero digits are significant
Zeros between two significant non-zero digits are significant
Zeros to the left of the first non-zero digit (leading zeros) are not significant
Zeros to the right of the last non-zero digit (trailing zeros) in a number with the decimal point are significant
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. 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. If it is desired that the trailing zeroes in an integer are seen as significant figures you can prefix the number with a dot (.).
The following table shows some examples of digits and their precision:
Value expression | Precision |
0.065 | 2 |
0.06500 | 4 |
3020.40 | 6 |
8002 | 4 |
1000. | 4 |
1 * 10^3 | 1 |
1000 | undefined |
2 + 3 | undefined |
Feedback, comments, questions
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