Year 12 Scientific Skills – Errors

WORKING SCIENTIFICALLY: ERRORS, Fair Test etc.

 

  1. Outlier/Anomalies     

These are values in a set of results which are judged not to be part of the variation caused by random uncertainty.

 

Question 1: Matthew records the current in a resistor for a certain voltage and takes repeat readings, some of which are shown below:

 

Resistance (Ω) current (A)
1 2 3 4 mean
20 0.25 0.28 0.47 0.26
30 0.16 0.17 0.15 0.16
  1. Highlight the anomaly/outlier  in the table.
  2. Correctly determine the mean for each row.

 

  1. Measurement error: The difference between a measured value and the true value.

 

Question 2:  Simon measures the mass of a mug as being 250 g, but its true value  is actually 260 g. The difference is a measurement error.

(True value is the value that would be obtained in an ideal measurement. An ideal measurement is one that would have no errors at all)

           Calculate the percentage error in Simon’s measurement.

 

  1. Uncertainty

The interval within which the true value can be expected to lie, with a given level of confidence or probability, e.g. “the temperature is 20°C ± 2°C, at a level of confidence of 95%.”

The symbol ± is called “plus or minus”, and in the example above means “plus or minus 2°C” – i.e. the temperature is most likely to be between 18°C and 22°C.

The “level of confidence” expresses how certain the scientists are of their claim that the temperature is in the range 18—22°C.

 

Question 3:(a)  State the mean and the uncertainty for the following data:

                   33, 36, 28, 37, 29, 27, 30, 31

              

Question 4: In conducting an experiment comparing the speed of sound to the air temperature, Amasha’s thermometer has units of 1 o C and you have found the air temperature to be 20 o C. Calculate

  1. The absolute uncertainty
  2. The percentage uncertainty.

 

  1. Random Errors

 

These cause readings to be spread about the true value, due to results varying in an unpredictable way from one measurement to the next.

Random errors are present when any measurement is made, and cannot be corrected. The effect of random errors can be reduced by making more measurements and calculating a new mean.

Random errors may be caused by human error, a faulty technique in taking the measurements, or by faulty equipment.

 

Question 5: Fawad and Andrew are both timing a very fast pendulum with a stopwatch. Andrew can’t count the swings accurately as it is just too fast to keep up – this introduces a random error in his readings as he may think he has counted 20 swings when in fact it was 21.

Fawad doesn’t use the stopwatch very well. Although he starts it fairly accurately, he panics when having to stop it and is either too early or late. This is a random human error.

 

Suggest how Fawad and Andrew can improve the reliability of their data. Explain your answer.

 

Question 6: Matthew records the current in a resistor for a certain voltage and takes repeat readings, some of which are shown below:

Resistance (Ω) current (A)
1 2 3 4 mean
20 0.25 0.28 0.47 0.26
30 0.16 0.17 0.15 0.16

 

  1. Explain how Matthew’s table shows a random error.
  2. Explain how to improve the accuracy of the data in Matthew’s experiment.

 

  1. Systematic errors

 

These cause readings to differ from the true value by a consistent amount each time a measurement is made.

Sources of systematic error can include the environment, methods of observation or instruments used.

Systematic errors cannot be dealt with by simple repeats. If a systematic error is suspected, the data collection should be repeated using a different technique or a different set of equipment, and the results compared.

e.g. A systematic error occurs when using a wrongly calibrated instrument.

E.g. Ashley’s pendulum timing experiment was made worse by the fact that she also began counting at ‘1’ not ‘0’. So all her times, in addition to random in her counting, were also short of one full swing each making her calculated times all smaller than the ‘true values’.

 

7 FAIR TEST

A fair test is one in which only the independent variable has been allowed to affect the dependent variable.

A fair test can usually be achieved by keeping all other variable constant.

 

 

Question 7

Swee Yong and Pavan are investigating how the electrical resistance of wires changes with length. Unfortunately both of them let the current get too high for shorter wires, which dramatically increases their temperature. Since temperature affects resistance (in addition to the length), it is not a fair test.

 

  1. Identify the independent and dependent variables in their investigation.
  2. Explain why their experiment is not a fair test.  
  3. What could they do to make it a fair test?

Year 12 Physics – Working Scientifically Part 1 Steps in Depth Studies

Steps in Depth Studies/Scientific Investigation

 

Steps What the step involved:
  1. Planning
  • Writing a Hypothesis (Questioning and Predicting)
  • Researching background information (literature review), which aids you to refine or evaluate your hypothesis/question (to ensure you wil 
  • Writing the Method for a valid scientific investigation (evaluate methods and secondary sources;list of equipment,  logical steps, consider ethical issues)
    2. Conducting the investigation   
  • Carrying out a valid scientific investigation (it could be an experiment or a scientific investigation using secondary data sources). In conducting an experiment, ensure it is done safely, appropriate measuring devices or appropriate technology is used.
  • Data collecting (in an experiment) may involve recording/readings from instruments, organising (tables with correct units). Data collection (using secondary sources) may involve recording or organising (tables with correct units.
3. Analysing and interpreting data
  • Analysing data involves searching for some trends or patterns.
  • Studying sets of data to see if they fit the mathematical formula.
  • Evaluating data to draw or justify the conclusion, test hypothesis (correct or incorrect), modifying the hypothesis,  recommending further testing or improving the method.
4. Communicating
  • Writing a scientific report, designing a poster, making a video/film presentation, delivering an oral presentation, making a  (may involve other forms to communicate scientific ideas).
  • In any one of the above, appropriate scientific principles/terminology/language should be used and effective visualisations/technologies to convey scientific ideas.   

 

Physics NEW (Implemented from 2018)

Physics NEW (Implemented from 2018)

View course

Supporting documents:

Course No:

  • 11310 Year 11 Physics
  • 15330 Year 12 Physics.

2 units for Year 11 (Preliminary) and Year 12 (HSC).

Year 11 Course Structure and Requirements

Year 11 course

 

(120 hours)

Working Scientifically Skills Modules Indicative hours Depth studies
Module 1

Kinematics

60 *15 hours

in Modules 1–4

Module 2

Dynamics

Module 3

Waves and Thermodynamics

60
Module 4

Electricity and Magnetism

 

*15 hours must be allocated to depth studies within the 120 indicative course hours.

Year 12 Course Structure and Requirements

Year 12 course

 

(120 hours)

Working Scientifically Skills Modules Indicative hours Depth studies
Module 5

Advanced Mechanics

60 *15 hours

in Modules 5–8

Module 6

Electromagnetism

Module 7

The Nature of Light

60
Module 8

From the Universe to the Atom

 

*15 hours must be allocated to depth studies within the 120 indicative course hours.