Practical Skills Flashcards
What is resolution of a measuring device?
The smallest division on the scale
In experiments what is precision?
A measure of the spread of the values about a mean value
(high presiscion = small spread)
Random errors determine precision of data
How is precision different to accuracy?
Precision is how close the values are to a mean value
Accuracy is how close that mean value is to the actual value
Results can be precise but inaccurate (eg with a systematic error)
What makes a measurement accurate?
If it is close to the true value (within its absolute uncertainty)
What is a measurement error?
Taking a reading and that is different to the actual value
(caused by random or systematic errors)
What are the 2 types of measurement errors?
**1. Random
2. Systematic **
Subcategories: zero, callibration, parallax, reaction time
What is an anomaly?
An incorrect measurement outside of the range of uncertainty
How do you deal with anomalies in results?
- Repeat measurement if possible
- If not discount anomalous result
What is a random error?
Something that causes results to be randomly spread out around a true value (eg repeat measurements for freefall)
How do you reduce random errors in experiments?
Take repeat measurements and calculate averages
What is a systematic error?
An error that causes all results to be affected by the same amount (eg reaction time using stopwatch)
Can be caused by miscalibrated equipment (zero error)
How do you reduce systematic errors in experiments?
Ensure equipment is correctly calibrated
What is a parallax error?
The viewing angle affects the measurement
What 2 things do you do to reduce parallax errors in experiments?
- Bring eyeline as level with scale as possible
- Place measuring equipment as close to object as possible
What type of error is this?
Random error (Reduced taking repeats and average)
What type of error is this?
Parallax
What type of error is this?
Systematic
What kind of error is this?
Systematic
What makes an experiment a fair test?
Only one variable is changed (independent variable) to affect the dependent variable
For a scientific result to be accepted what 2 conditions must the experiment meet?
- Repeatable - If you can perform the experiment again and get the same result
- Reproducible - If someone else can perform the same experiment and get the same result
In experimental science what is absolute uncertainty?
The interval which the actual value of a measurement is expected to lie in
How is absolute uncertainty for a measurement determined?
- = resolution of equipment
or - Half range of repeats (discount anomalies)
What is the absolute uncertainty here?
±1𝑚𝑚
What is the absolute uncertainty here?
±0.01V
What is the absolute uncertainty here?
±0.05s
What is the reading on this venier scale?
10.02cm
What is the reading on this venier scale?
3.34cm
What is the reading on this micrometer scale?
10.83mm
What is the reading on this micrometer scale?
2.88mm
How do you calculate percentage uncertainty?
How do you combine uncertainties for measurements with different units?
Add together their percentage uncertanties
Do not add together their absolute uncertainties
How do you combine uncertainties for measurements with the same units?
Add together their absolute uncertanties
Do not need to add together their percentage uncertainties
What has been done wrong here?
Cannot add together absolute uncertainties if units are different
Must only add together percentage uncertainties
What has been done wrong here?
Anomalous result shouldn’t have been included
What do error bars show?
Graphically shows absolute uncertainty in one of the measurements
(x or y axis)
What do error boxes show?
Graphically shows absolute uncertainty in both of the measurements
(x and y axis)
What is the absolute uncertainty in this reading?
How do error bars help with analysing results?
- Visually show precision of experiment
- Help identify anomalous results
- Allow more precise gradient line to be drawn
How do you work out the percentage uncertainty of a gradient?
How do you work out the percentage uncertainty of a y-intercept?
How do you combine these uncertainties?
- Add together percentage uncertainties
- Multiply power by corresponding percentage uncertainty
How do you combine these uncertainties?
- Add together percentage uncertainties
- Multiply power by corresponding percentage uncertainty
Which of these experiments is more successful?
g2. As the actual value is within it’s absolute uncertainty
What is wrong here?
Absolute uncertainties must match decimal points of measurements
What is wrong here?
Calculated values can’t have higher precison than source values
What is wrong here?
Units should be put in the column headings
What is wrong here?
Values in each column should have the same number of decimal places
What is wrong here?
Scale should go up in 1s, 2s or 5s
What is wrong here?
Axis need titles and units
What is wrong here?
Data take up less than half of the page
Instead ** use a broken axis if possible**
What is wrong here?
Data points should always be plotted with crosses (not dots)
What is wrong here?
Don’t force Line of Best Fit through origin
What is wrong here?
Gradient triangle should be as large as possible
How do you reduce the percentage uncertainty of a measurement?
- Use measuring device with higher precision
- Take bigger measurements (eg use bigger distances in experiment)
In this SHM experiment why is time measured over 10 oscillations?
Reduces absolute uncertainty of each oscillation by 10x
In this double slit experiment why is distance measured between 11 dots?
Reduces absolute uncertainty of each distance by 10x
