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%
