1.1 measurements and their errors Flashcards
What are SI units?
Fundamental (base) units of physical quantities
What physical quantity is measured in mol?
An amount of substance
Express 60Tohms in standard form
6x10^13 (T is tera x10^12 )
Write 0.000005m as a suitable prefix
5μm μ=10^-6
What is the actual value of 8M ohms?
8x10^6 ohms
What is 6000pF in nF
6nF as 1 nano = 1000 pico’s
What multiplier is associated with the prefix femto
10^-15
Express 7G ohms in standard form
7x10^9 ohms
What is a random error?
An error that affects precision and cannot be removed , causing changes in measurements
What is a systematic error ?
An error that affects accuracy and is caused by faulty equipment or faults in the experimental method , causing the result to be too large/ small by the same amount each time
What are 3 ways to reduce random error?
1) take at least 3 repeats and calculate an average
2) use a computer or data logger
3) Use higher resolution equipment
How can systematic errors be reduced ?
By calibrating the equipment before use
e.g: zero the balance when it is empty
What is precision?
consistent measurements that fluctuate about a mean value - this does not mean they are accurate
What is repeatability ?
The original experimenter can redo the experiment with the same equipment and method and still get the same results
What is reproducibility ?
If the experiment is done by somebody different with different equipment and different techniques and still get the same results
What is meant by resolution ?
The smallest change in quantity being measured giving a recognisable change in reading
What is meant if a value is accurate ?
If the value is close to the true value
What is absolute uncertainty ?
Uncertainty given as a fixed value
e.g: 7+/- 0.6V
How can percentage and fractional uncertainty be reduced?
Measure larger quantities
What is the difference between a reading and a measurement?
Readings are when a value is found a measurement is when the difference between 2 meanings is found
What is the uncertainty of a device?
The uncertainty of a reading is +- half the smallest division
3 times are given : 3.1 ,3.2 , 3.6 . Find the mean and absolute uncertainty.
Mean: 3.1+3.2+3.6 = 9.9 9.9 /3 = 3.3
Uncertainty = half range 3.6-3.1= 0.5 0.5/2 = 0.25
Answer : 3.3+-0.25
What is wrong with writing 7+-0.673V?
Uncertainty should always be given with the same number of significant figures as the answer ie: 7=+-0.7
A force of 91+-3N is applied to a mass of 7+-0.2kg what is the acceleration?
91/7=13ms^-2
uncertainty percentage = (0.2/7)100+ (3/91)100= 6.2%
a= 13ms^-2+-6.2%
When drawing a line of best fit on a graph with error bars on what must you do ?
Make sure the line of best fit goes through all the error bars
How do you find the uncertainty in the gradient of the line of best fit?
Draw the steepest or the shallowest line of worst fit that still goes through the error bars
workout the gradient of the line of worst and best fit and the difference between the 2 is the uncertainty?
How do you workout the uncertainty in the y-intercept of the line of best fit ?
best fit y intercept - worst fit y intercept
What is an order of magnitude?
Powers of 10 which describe the the size of an object , and which can also be used to compare sizes between objects
What is estimation?
A skill physicists must have to approximate the values of physical quantities, in order to make comparisons or to check if answers are reasonable
Adding or subtracting uncertainties
adds absolute uncertainty
multiplying or dividing uncertainty
add percentage uncertainty
raising uncertainty to a power
times percentage uncertainty by power
when multiplying to a constant with uncertainties
multiply the uncertainty by constant not the percentage uncertainty
