Practical Skills Flashcards
How can one evaluate an experimental design?
The experiment can be repeated and the results compared to those achieved previously to determine the** reproducibility** (whether similar results can be achieved or not). This is known as** peer review.**
Define what a limitation of an experiment’s design is
A limitation is any design flaw or fault that affects the accuracy of an experiment. To produce valid results, these must be identified and removed/corrected.
Give 5 common examples of limitations of procedures
- Parallax error when reading scales
- Not repeating measurements to reduce the effect of random errors
- Not checking for zero errors tor reduce effect of systematic error
- Not using a fiducial marker
- Equipment with poor precision and resolution
Define accuracy
Accuracy is how close a result is to the true value.
Accuracy is affected by the presence of systematic errors
Define precision
Precision is how similar repeated results are to one another
Precision is affected by the presence of random errors
Give a definition of an independent variable
An independent variable is the variable that is changed throughout an experiment. (Plotted on the x-axis)
Give a definition of a dependent variable
A dependent variable is the variable that is measured to determine the outcome of an experiment.
Give a definition of a control variable
A control variable is a variable that could affect the results of the experiment and so must be controlled or monitored to remain the same, allowing for valid results to be produced.
Give a definition of a variable
Any factor that can change or be changed in an experiment.
Define an error
The difference between a measured value and a true value
Name the two main categories of error
- Systematic error and 2. Random error
Define random error
2 parts
Random error is an error in a measurement due to small uncontrollable effects. They contribute to the uncertainty of a measurement.
How does random error affect measurements?
(When do they occur, what value do they take etc. 5 parts)
- They are present in every measurement
- Random error varies between successive measurements
- Equally likely to be positive or negative
- Affects measurement in unpredictable way
- They affect the precision of results
Name three examples of factors that influence random errors
- Quality of measuring instruments
- Judgement in reading scales (e.g. inconsistent direction when reading a scale - parallax error)
- Small variations in temperature or light levels
How do you reduce the effect of random error?
Repeating measurements at least 3 times, eliminating anomalies and calculating a mean from them.
Define systematic error
A systematic error is an error due to the measured value differing from the true value by the **same amount **each time.
How does systematic error affect measurements and what are characteristics of systematic error?
(4 parts)
- Systematic error affects all measurements in the same way
- Can be difficult to spot due to results differing by same value
- They cannot be minimised by repeating measurements.
- They affect the accuracy of results
Name two examples of factors that influence systematic error.
- Instrument used incorrectly by student e.g. parallax error (if consistent)
- Incorrect calibration of measuring instruments
How can a systematic error be corrected?
If systematic error is identified, corrections/adjustments should be made to the technique OR instruments should be recalibrated or different instruments should be used.
Give an example of a systematic error and explain what it is
Zero error
Type of systematic error that occurs when an instrument gives a reading when the true reading is zero. Can be accounted for when results are recorded.
Give an example of a systematic error and explain what it is
Zero error
Type of systematic error that occurs when an instrument gives a reading when the true reading is zero. Can be accounted for when results are recorded.
Suggest how a parallax error can be reduced
By using a fiducial marker: a thin marker, such as a splint, that is used to ensure readings are taken from the same place each time. They are used to improve the accuracy of measurements.
Define what the resolution of a measuring instrument is
Resolution is the smallest change in a quantity that causes a visible change in the reading that a measuring instrument records.
How is absolute uncertainty of an apparatus determined on an analogue instrument?
It is half the smallest graduation/scale division as the reading must be rounded up or down to the nearest scae division.
Explain how the absolute uncertainty for a protractor is determined.
Angles are measured to the nearest degree, therefore half the smallest scale division is 0.5 degrees.
Explain how absolute uncertainty of a stopwatch is determined
Time is measured to the nearest 0.01s, however reaction time is 0.1-0.5s, so a degree of precision of 0.1-0.5s is much more reasonable. Therefore the uncertainty is 0.05-0.25s.
Define an analogue scientific instrument
They transfer information through electric pulses of varying amplitude. They are cheaper but have lower accuracy and resolution and also more sensitive, therefore more difficult to read fluctuating values.
Define an analogue scientific instrument
They transfer information through electric pulses of varying amplitude. They are cheaper but have lower accuracy and resolution and also more sensitive, therefore more difficult to read fluctuating values.
They are subject to parallax error as they typically use a pointer
Define an analogue scientific instrument
They transfer information through electric pulses of varying amplitude. They are cheaper but have lower accuracy and resolution and also more sensitive, therefore more difficult to read fluctuating values.
Define a digital scientific instrument
They translate information into binary (0 or 1) format that can then be read and analysed by a computer. They have greater accuracy and resolution and not subject to parallax error. Both analogue and digital are subject to zero error.
Suggest how uncertainty in a measurement of period time can be reduced
It can be reduced by measuring many oscillations to calculate the average time for one oscillation OR by increasing the total time taking for multiple swings (this is when applied to a pendulum).
Suggest how uncertainty in a measurement of period time can be reduced
It can be reduced by measuring many oscillations to calculate the average time for one oscillation OR by increasing the total time taking for multiple swings (this is when applied to a pendulum).
Suggest how uncertainty in a measurement of period time can be reduced
It can be reduced by measuring many oscillations to calculate the average time for one oscillation OR by increasing the total time taking for multiple swings (this is when applied to a pendulum).
Suggest how set squares and plumb lines can be used to decrease uncertainty and reduce the effect of random error
Set square can be used to determine whether an object is vertical (such as a ruler secured by a clamp), whether two objects are at right angles to each other or whether two lines are parallel.
A plumb line can be used to determine if a setup is verticall aligned accurately in combination with a set square.
Suggest how set squares and plumb lines can be used to decrease uncertainty and reduce the effect of random error
Set square can be used to determine whether an object is vertical (such as a ruler secured by a clamp), whether two objects are at right angles to each other or whether two lines are parallel.
A plumb line can be used to determine if a setup is verticall aligned accurately in combination with a set square.
Suggest how set squares and plumb lines can be used to decrease uncertainty and reduce the effect of random error
Set square can be used to determine whether an object is vertical (such as a ruler secured by a clamp), whether two objects are at right angles to each other or whether two lines are parallel.
A plumb line can be used to determine if a setup is verticall aligned accurately in combination with a set square.
Define an anomaly/outlier
Value in a set of results tht is judge not to be part of the inherent variation (aka random error).
