Refining of Experimental Design (OCR A Level Physics)

Refining of Experimental Design

• An important part of experimental physics is being able to identify problems in the experimental design

• Once the problems have been identified, then it is possible to suggest improvements to the procedures and apparatus

• In order to evaluate the procedure, it is important to understand that there is uncertainty in every measurement

  • Every instrument is limited by its resolution

• Uncertainties are introduced predominantly by the type of apparatus used and the way it is used resulting in

  • Systematic errors

  • Random errors

Random Error

• Random errors cause unpredictable fluctuations in an instrument’s readings as a result of uncontrollable factors, such as environmental conditions

• This affects the precision of the measurements taken, causing a wider spread of results about the mean value

• To reduce random error:

  • Repeat measurements several times and calculate an average from them

Systematic Error

• Systematic errors arise from the use of faulty instruments used or from flaws in the experimental method

• This type of error is repeated consistently every time the instrument is used or the method is followed, which affects the accuracy of all readings obtained

• To reduce systematic errors:

  • Instruments should be recalibrated, or different instruments should be used

  • Corrections or adjustments should be made to the technique

Zero Error

• This is a type of systematic error which occurs when an instrument gives a reading when the true reading is zero

• This introduces a fixed error into readings which must be accounted for when the results are recorded

Resolution

• Resolution is the smallest change in the quantity being measured of a measuring instrument that gives a perceptible change in the reading

• For example, the resolution of a wristwatch is 1 s, whereas the resolution of a digital stop-clock is typically 10 ms (0.01 s)

• In imaging, resolution can also be described as the ability to see two structures as two separate structures rather than as one fuzzy entity

Good resolution and poor resolution in an ultrasound scanner. The good image manages to resolve the two objects into two distinct structures whereas the poor image shows one fuzzy entity.