6 Common Mistakes Mistake 1 Incorrect interpretation of

6 Common Mistakes

Mistake #1: Incorrect interpretation of Key Verbs • A large number of students fail to respond to questions involving ‘Compare’ or ‘Explain’ or ‘Assess’ correctly. For example students are listing instead of describing or giving a description not an explanation. • Did you know that HSC Marking Centre advises the use of tables to answer questions involving compare, assess, discuss and evaluate?

• Consider the Sample Responses to 2006 HSC question given below by the Board of Studies: Assess the impact on society and the environment of the potential applications of superconductors.

Mistake #2: Insufficient Working for Calculations Did you know that 2 marks are allocated in a simple calculation question? • 1 mark for correct formula and substitution and • 1 mark for the correct answer In questions requiring numerical answers, you should always • show the working in a clear and logical fashion • round-off answers at the end of the calculation instead of during the parts of the calculation.

RUDE • https: //www. youtube. com/watch? v=q 2 hf. MH n. Bk 20

Mistake #3: Write units. I mean correct SI Units! Students forget to provide the correct units with their numerical answers. What is wrong with this student’s answer regarding the magnitude of acceleration? • “The acceleration of the rocket is 15 m/s. ” Make sure you know the SI units for the following: • mass • velocity • acceleration • force • energy • frequency • wavelength • current • potential difference • resistance

Mistake #4: Line of Best Fit? • When drawing a line of best fit, students must identify and eliminate any outliers before determining the trend.

• If a student does not recognise the outlier then he/she will draw an incorrect line of best fit (dotted line). However once you remove the outlier from trend, then you can draw a correct line of best fit (solid line).

Mistake #5: Confusion about Validitiy, Reliability and Accuracy? •

Mistake #6: Human error is not a valid type of experimental error! • When students are asked about how to improve the reliability and accuracy of the experimental results, most state “reduce human error!” Human error is not a valid type of experimental error! The two types of experimental error explored in physics experiments are random and systematic errors.

Random errors are caused by unknown and unpredictable changes in the experiment, These are statistical fluctuations in both directions about the true value thus repetition and statistical analysis can reduce the effects. To help reduce random errors: • Make sure you know how to read the scales on the instruments and that you align yourself properly each time you take a measurement. • Take multiple measurements (repetition increases reliability!) and then take an average for the result Systematic errors are caused by measuring instruments being used incorrectly or problems with the instrument itself. Systematic errors limit accuracy. To help reduce systematic errors: • All instruments should be checked against a standard before use. Zero settings should be checked and adjusted (calibration!). • Instructions for the use of the instrument should be read and followed. • Corrections for instrument bias should be made (if necessary).

Type of Error Example How to minimize it Random errors Take more data. Random You measure the mass of a ring errors can be evaluated through three times using the same balance statistical analysis and can be and get slightly different values: reduced by averaging over a large 17. 46 g, 17. 42 g, 17. 44 g number of observations. Systematic errors • Systematic errors are difficult to detect and cannot be analyzed The cloth tape measure that you statistically, because all of the data use to measure the length of an is off in the same direction (either object had been stretched out from to high or too low). Spotting and years of use. (As a result, all of your correcting for systematic error length measurements were too takes a lot of care. How would you small. )The electronic scale you use compensate for the incorrect reads 0. 05 g too high for all your results of using the stretched out mass measurements (because it is tape measure? improperly tared throughout your • How would you correct the experiment). measurements from improperly tared scale?

Deriving Formulae

HSC Investigations

Scientists