Foundations Of Physics Flashcards
How is the uncertainty calculated when given a set of values of repeat readings?
Uncertainty=Range/2
Definition of Precise
A set of results/data is precise if the values are clustered closely together
Definition of Accuracy
A measurement is accurate if it is close to the true value
Tera
10^12 (T)
Giga
10^9 (G)
Mega
10^6 (M)
Kilo
10^3 (k)
Centi
10^-2 (c)
Milli
10^-3 (m)
Micro
10^-6 (µ)
Nano
10^-9 (n)
Pico
10^-12 (p)
Femto
10^-15 (f)
Deci
10^-1 (d)
cm^2—->m^2
Divide by 1x10^4
cm^3—->m^3
Divide by 1x10^6
Percentage Uncertainty
Percentage Uncertainty in a value= Uncertainty in Value/Value x 100
Random Error
What is it?
How does it affect results?
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 value.
How to reduce random error?
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 the readings obtained.
How to reduce systematic errors?
-Instruments should be recalibrated, or different instruments should be used
-Corrections or adjustments should be made to the technique
What is zero error?
This is a type of systematic error which occurs when an instrument gives a reading when the true value is zero.
How to reduce zero error?
Since zero error 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.
What do you do when adding or subtracting with uncertainties?
You add together the absolute uncertainties.
What do you do when multiplying or dividing with uncertainties?
You add together the percentage uncertainties.
When an uncertainty is raised to a power what do you do?
e.g. z=x^3 and x=1.35±0.25cm . Determine z and the absolute uncertainty in z.
You work out the percentage uncertainty as normal and then you multiply by the power.
Answer:
-> z = 1.35^3 = 2.460cm^3
-> %U in z = 3x(0.25/1.35x100)=55.6%
-> Absolute uncertainty in z = 2.460x(55.6/100) =1.37
-> z = 2.46±1.37 cm^3
How to find uncertainty from the gradient of a graph?
-> Draw the line of best fit
-> Draw the line of worst fit by drawing line through max error bar and lowest error bar to make sure
-> Calculate gradients for the line of best fit and the line of worst fit
-> Then find the difference in gradients
-> %U in gradient= (difference in gradient/gradient of line of best fit) x 100
How do you determine the percentage uncertainty of the y intercept?
->Find y intercept from the line of best fit
-> Draw line of worst fit
-> Find y intercept from line of worst fit
-> %U in y intercept: (Difference in y intercepts/y intercept of line of best fit) x 100
How to calculate percentage difference?
Percentage difference= (Experimental value - Accepted value/ Accepted value) x 100
How to calculate the uncertainty in a reading?
±half the smallest division
How to calculate the uncertainty in a measurement?
at least ±1 smallest division
How to calculate the uncertainty in digital readings?
±the last significant digit unless otherwise quoted
What effect do systematic errors have on a graph?
Move the line of best fit away from when it should be
Find n for 1mm^3 = 1x10^n m^3
n = -9
1mm^3 = 1x10^-9m^3
What are repeatable measurements?
Measurements where the same results are obtained if the same person uses the same equipment
Find n for 1cm^2 = 1x10^n m^2
n=-4
1cm^2 = 1x10^-4m^2
How can vectors be added?
Draw the individual vectors tip to tail and find the single vector that goes from start to finish
What do error bars on a graph represent?
The absolute uncertainties in the measurement data
What is a parallax error?
A systematic error that occurs when the line of sight of a person is not perpendicular to the scale.
What apparatus is used to measure force?
Newtonmeter
What apparatus is used to measure mass?
Digital balance
Find n for 1cm^3 = 1x10^n m^3
n = -6
1cm^3 = 1x10^-6 m^3
What apparatus is used to measure weight?
Newtonmeter
Find n for 1mm^2 = 1x10^n m^2
n = -6
1mm^2 = 1x10^-6 m^2
What apparatus is used to measure lengths of 0-10cm?
Vernier callipers
What apparatus is used to measure volume of a liquid?
Measuring cylinder
What apparatus is used to measure lengths of 1-20m?
Tape measure
Name the 7 SI base quantities and give their units:
Mass - Kilogram - kg
Length - Metre - m
Time - Seconds - s
Electric current - Ampere - A
Temperature - Kelvin - K
Amount of substance - Mole - mol
What is meant by a homogeneous formula?
A formula where the units are the same on each side (checked by converting to SI base units)
What apparatus is used of measure lengths of 0-100cm?
Metre rule
What apparatus is used to measure lengths of 0-5cm?
Micrometer
What apparatus is used to measure temperature?
Digital thermometer / temperature probe
What are reproducible measurements?
Measurements where similar results are obtained if a different person uses a different method or equipment
What effect do random errors have on a graph?
Scatter points about the line of best fit
What apparatus is used to measure elapsed time?
Stop clock
