National 5 Physics: Command Words

The following terms may appear in questions in the National 5 Physics exam. An explanation is provided which will help you understand what you have to do when you see these terms appear.Identify, name, give, or state – Usually worth one mark, an explanation of your answer is not required. Describe – You must provide a statement or structure of characteristics and/or features. Explain –You need to provide details as to how something works or reasons as to why something is happening. You should relate the cause and effect and/or make the relationships between things clear. You should use directly relevant and correct physics. Sometimes this question will also include a phrase like “explain in terms of…” it is therefore vital that your explanation includes the words/terms mentioned. Determine / Calculate – Your answer will be a numerical value with unit, calculated from given facts, figures or information usually awarded three marks. The first mark for selecting the correct formula, the second mark for correct substitutions and the third mark for the final answer with unit to an appropriate number of significant figures, correctly rounded. The number of significant figures should be the same as the least precise numerical data given in the question. The final mark will not be awarded if the answer has more than two more or fewer than one less than the correct number of significant figures. Do not copy down answers from your calculator that contain a large number of significant figures or use ellipses. Do not round values at an intermediate stage, use the unrounded number in your calculator. Do not copy down answers from your calculator that contain a large number of significant figures or use ellipses. Sometimes a calculate question has more than three marks with a mark awarded for another calculation or for selecting a value(s) from a table or graph or analysing results of an experiment or previous calculation. Estimate – Your answer is an approximate value for something. This estimate may be based upon a calculation or be estimated by comparison to a previous response. Justify – This term will often appear as a follow up to a state question. Here you must provide a reason for the statement/suggestion/conclusion you provided. This might be by identifying an appropriate relationship and the effect of changing variables. You can justify using a calculation but remember to also state your conclusion.

1

Must Justify - You must not only state or select the correct response, but also provide supporting justification to achieve any marks. If you provide no reason, then even if you have the correct statement you will receive no marks. Show that – You should “show” a particular answer is correct, you must start your response with an appropriate relationship, show the correct substitutions, and end with the final answer as it is shown, including the correct unit, to obtain all the marks available. If you do not start with showing the correct relationship, there will be 0 marks, these are usually two-mark questions. Predict – You must suggest what may happen based upon available information. This will involve some comparison of data and will often require you to get your answer by analysing a graph, a table or a set of results.Suggest how/why – This is like an explain question, but is about applying knowledge and understanding to a new situation. Often it relates to providing a possible improvement to an experiment or a reason for why something hasn’t worked as well as it should. Often several responses are acceptable: marks will be awarded for any suggestions that are supported by knowledge and understanding of physics. Be aware if you put more than one response any incorrect one will prevent a mark for a correct one. Using your knowledge of Physics, comment on…. - These are known as open-ended questions as they can have a range of different answers. You should make statements of relevant and correct physics at National 5 level. You can do this by providing explanations, calculations, justifications, suggestions and even drawings…… You will gain credit for the breadth and/or depth of your answer. You should answer in sentences and not in bullet points and making sure you refer to the question asked. Draw – You need to draw something, it could be anything, a normal or ray diagram, a force or vector diagram or circuit symbol/diagram etc. It is a essential to use a ruler unless you are intentionally drawing a curve.

2

Other language

Reliability

A reliable experiment is one that is a fair test. Reliability is a measure of how dependably the data is from an experiment. At National 5 an experiments should be repeated and a mean average calculated to improve the reliability of the data. The number of repeats required will depend upon the variation in the readings measured. If there is little variation in the data, further repeats would not improve the reliability of the experiment. An experiment could also be made more reliable from an increase in the range of the variable you are changing. Often a change in the setup of the experiment can make it more reliable by making it more of a fair test (keeping all the variables except the independent variable (the one you change) the same). Example

Experiment 1 is more reliable than experiment 2 as the repeated results are all the same. It would be beneficial for experiment 2 to have been repeated more often to improve the reliability. In experiment 2 the reading at 45 degrees should definitely have been repeated as the two values are quite different. The experiment could also be made more reliable from an increase in the range of angles of slope from say 5°to 60 degrees. Experiment 1Angle of slope (°)

Speed of car (m/s)

Speed of car (m/s)

Average Speed of car (m/s)

10 1·4 1·4 1·415 1·6 1·6 1·620 1·8 1·8 1·825 2·0 2·0 2·030 2·2 2·2 2·240 2·3 2·3 2·345 2.4 2.4 2.4

Experiment 2Angle of slope

(°)Speed of car (m/s)

Speed of car (m/s)

Average Speed of car

(m/s)10 1·5 1·3 1·415 1·7 1·5 1·620 1·7 1·9 1·825 2·1 1·9 2·0

3

30 2·1 2·3 2·240 2·4 2·2 2·345 2·1 2·7 2·4

PrecisionPrecision can be improved by using different equipment, for example a ruler that only has a centimetre scale is less precise than a ruler that has a millimetre scale. Another example would be a mass balance (scales) that measure to 0·1 g would be more precise than one that measures to the nearest 1 g. Example

Experiment 2 is more precise than experiment 1 as the speed has been measured to more significant figures. It is important to write 2·30 rather than 2·3 if the second decimal place is shown, just writing 2·3 could mean a value between 2·25 and 2·34

Experiment 1Angle of slope (°)

Speed of car (m/s)

Speed of car (m/s)

Average Speed of car (m/s)

10 1·4 1·4 1·415 1·6 1·6 1·620 1·8 1·8 1·825 2·0 2·0 2·030 2·2 2·2 2·240 2·3 2·3 2·345 2.4 2.4 2.4

Experiment 2Angle of slope

(°)Speed of car (m/s)

Speed of car (m/s)

Average Speed of car

(m/s)10 1·39 1·41 1·4015 1·61 1·59 1·6020 1·79 1·81 1·8025 2·01 1·99 2·0030 2·21 2·19 2·2040 2·30 2·30 2·3045 2·40 2·40 2·40

Precision can also mean how close a calculated value is to the expected value. For example an experiment to calculate the resistance of a resistor by Ohm’s law (by measuring current and voltage) might calculate a value of 11·0 ohms. This can be compared to the expected value from the supplier of 10·0 ohms.

4

5

AccuracyAccuracy is the degree to which a measurement represents the true/actual value of something. Simply put: How close a measurement is to the true value? An accurate measuring instrument, say a thermometer, is one whose readings confirm a known result. A series circuit that has two ammeters connected could be used to check the accuracy of the ammeter reading. Where time is being measured in an experiment, the time recorded may be inaccurate due to human reaction time. If an experiment has an aim to find out a constant such as the specific heat capacity of a metal, an accurate answer would be a result that is close to this number. An inaccurate experiment to measure the specific heat capacity of a metal might lack the use of insulation to prevent heat energy being transferred to the surrounding air. A student trying to calculate the frequency of a swing would have a more accurate answer if they measured a number of swings (say 5 or 10) rather than just measuring one swing.

6

Examples

Draw, State, Determine and Justify (by calculation) and Explain (2017 – Section 2 – Question 1)

answer

answer

7

answer

answer

The direction of the electron flow is continually changing back and forward/to and fro.Additional Guidance

The answer must be in terms of electrons/charges (NOT current alone). You must indicate repeated changing of direction

8

Identify (2019 – Section 2 – Question 10)

answer

(black-bulb) thermometer 1

The part of the response in a bracket is not essential to get the mark.

9

Show that (2014 – Section 2 – Question 3)

10

Show that (2019 – Section 2 – Question 2)

11

Must Justify (2019 – Section 2 – Question 5)

12

State and Justify (no calculation) (2017 – Section 2 – Question 11)

Answer Graph Q

answer

The time taken for the ball to reach the ground is equal to the time taken in the first serve. This is because the vertical/downward acceleration is the same.

13

Describe (2017 – Section 2 – Question 9(a))

answer

The forces are equal in size and opposite in directionor

The forces are balanced

14

State, Determine (by graph reading and also by calculation) and Predict (2017 – Section 2 – Question 6 (a) and (b))

answer

15

answer

4.4mmAdditional guidance

As you need to interpret the curve on the graph to get this answer, and answer of 4.3mm to 4.5 mm would be accepted.

answer

The first mark is awarded for ing evidence of 3 half value thicknesses (1). This is an unfamiliar context question and should not be confused with half-life, which you do learn about in the course. The second mark is awarded for the answer below:

answer

Additional guidance

For some questions (not this one) a numerical value is required when predicting – watch for this.

16

Calculate and suggest (2017 – Section 2 – Question 4 (a))

answer

Additional guidance

This answer could also be calculated using

Answer

Measure the time for more waves to pass or

Count the number of waves in a longer over a longer period of time or

Repeat (the measurement) and calculate the average

17