Measurement And Errors Flashcards
What is the SI unit for length?
Metre, m
What is the SI unit for time?
Seconds, s
What is the SI unit for mass?
Kilogram, kg
What is the SI unit for temperature?
Kelvin, K
What is the SI unit for electric current?
ampere, A
What is the SI unit for the amount of substance?
Mole, mol
What is the prefix represented by T and what power is it to?
Tera, 1 x 10^12
What is the prefix represented by Pand what power is it to?
Peta, 1 x 10^15
What is the prefix represented by G and what power is it to?
Giga, 1 x 10^9
What is the prefix represented by M and what power is it to?
Mega, 1 x 10^6
What is the prefix represented by k and what power is it to?
Kilo, 1 x 10^3
What is the prefix represented by h and what power is it to?
Hecto, 1 x 10^2
What is the prefix represented by da and what power is it to?
deca, 1 x 10^1
What is the prefix represented by d and what power is it to?
Deci, 1 x 10^-1
What is the prefix represented by c and what power is it to?
Centi, 1 x 10^-2
What is the prefix represented by m and what power is it to?
Milli, 1 x 10^-3
What is the prefix represented by (u-ish) and what power is it to?
Micro, 1 x 10^-6
What is the prefix represented by n and what power is it to?
Nano, 1 x 10^-9
What is the prefix represented by p and what power is it to?
Pico, 1 x 10^-12
What is the prefix represented by f and what power is it to?
Femto, 1 x 10^-15
What is an electron volt?
A unit of work (or energy) much smaller than a Joule
1eV = 1.6 x 10^-19J
How do you convert energy in J to energy in eV?
Energy in eV = energy in J / 1.60 x 10^-19
How to find kilowatt-hour (kWh)
1kW = 1000W and 1h = 3600 s
Then energy (w) = power (kW) x time(h)
1kWh = 1000Js^-1 x 3600s
1kWh = 3,600,000 J
What are SI units?
Fundamental base units of physical quantities
Is the SI unit for temperature ºC or K?
K, Kelvin as this is an absolute scale
Are Newtons, N, an SI unit?
No, they are not fundamental as the SI units for force are kgms^-2
Derive the SI units of energy.
Kinetic energy = 1/2 x mass x velocity squared
Units = kg x ms^-1 x ms^-1
= kgm^2s^-2
Derive the SI unit of force.
Force = mass x acceleration
Units = kg x ms^-2
= kgms^-2
Express 60T ohms in standard form.
6 x 10^13 ohms
the multiplier for tera is 10^12
Write 0.000003m with a suitable prefix
3 micro meters, symbol mu
What is the actual value of 8M ohms?
8 x 10^6 ohms
8,000,000 ohms
What is 6000pF in nF?
6nF, as 1 nano unit is 1000 pico units
What multiplier is associated with the prefix kilo, k?
x 10^3
What multiplier is associated with the prefix femto, f?
x10^-15
Express 7G ohms in standard form.
7 x 10^9 ohms
Express 6kWh in joules.
6kW = 6000 Js^-1
1 hour = 3600s
6kWh = 6000 x 3600 = 21.6 x 10^6 J
= 21.6MJ
What is a random error?
An error that affects precision and cannot be completely removes, it causes differences in measurements
What is a systematic error?
An error that affects accuracy and occurs due to faults in equipment or experimental method, causing the result to be too large/small by the same amount each time
What are three ways to reduce random error?
- Take at least 3 repeats and calculate the mean
- Use a computer or data logger
- Use higher resolution equipment
A mass balance reads 1004g when a 1kg mass is placed on it, is this a random error or systematic error?
Systematic as the reading is too high by 4g each time
State a cause of parallax error.
Reading a scale at a different angle each time, to correct this you should read scales at eye level or install a mirror behind if reading a dial
How can systematic error be reduced?
Calibrate apparatus before using e.g. zero the balance when it is empty
Is electronic noise in the circuit of an ammeter random error or systematic error?
It is random error as it will cause fluctuations in readings that affect precision and it cannot be removed
Why should you measure back ground radiation before measuring the radioactivity of a source?
So that only the source’s radioactivity is measured, by accounting for background radiation systematic error is reduced
What is precision?
Precise measurements are consistent, they fluctuate slightly about a mean value - this does not indicate the value is accurate
What is repeatability?
If the original experimenter can redo the experiment with the same equipment and method then get the same results, then it is repeatable
What is reproducibility?
If the experiment is redone by a different person or with different techniques and equipment and the same results are obtained, then it is repeatable
What is meant by resolution?
The smallest change in the quality being measured that gives a recognisable change in reading
What is meant if a value is accurate?
If the value is close to the true or accepted value
What is absolute uncertainty?
Uncertainty given as a fixed quantity, eg. 7 +/- 0.6V
What is the percentage uncertainty in 17 +/- 3A?
(3 / 17) x 100 = 17.647%
= 18%
What is the fractional uncertainty of 8 +/- 0.5m?
0.5 / 8 = 1 / 16
How can percentage and fractional uncertainty be reduced?
Measure larger quantities e.g. a longer rope with have a smaller percentage uncertainty than a shorter one
The time for 10 swings of a pendulum is 13 +/- 0.3s, what is the time and uncertainty from 1 swing?
1 swing = 13/10 = 1.3s
Uncertainty = 0.3/10 = 0.03s
Time = 1.3 +/- 0.03s
What’s the difference between a reading and a measurement?
Readings are when one value is found, measurements are when the difference between 2 readings is found
What is the uncertainty of a thermometer whose smallest division is 5ºC?
The uncertainty in a reading is +/- half the smallest division, so the uncertainty is +/- 2.5ºC
What is the percentage uncertainty in the measurement of a 2cm line?
Each end has an uncertainty +/- 0.5mm, so the total uncertainty in the measurement = +/- 1mm
% uncertainty = (1/20) x 100 = 5%
2+/- 5%
What is the uncertainty in the charge of an electron (1.6 x 10^-19 C)?
1.6 x 10^-19 =/- 0.1 x 10^-19 C
The time for a ball to drop are measured as 3.2s, 3.6s and 3.1s. Find the mean and absolute uncertainty of these times.
Mean: 3.2+3.6+3.1 = 9.9 9.9/3 = 3.3s
Uncertainty: (3.6-3.1) / 2 = 0.25
= 3.3+/- 0.3.s
What is wrong with writing 7 +/- 0.673V?
The uncertainty should be the same number of significant figures as the data ie. 7 +/- 0.7V
A thermometer with an uncertainty of 0.5K shows the temperature of water falling from 298 +/- 0.5K to 273 +/-0.5K, what is the difference in temperature and the uncertainty in this difference?
298 - 273 = 25K
0.5 + 0.5 =1K
Difference = 25 +/- 1K
When drawing a line of best fit on a graph with error bars, 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 a line of best fit?
Draw a steepest or shallowest line of best fit that goes through all error bars. Calculate the gradients of the best and worst line. The uncertainty is the difference between the two
How do you work out the uncertainty in the y-intercept of a line of best fit?
The uncertainty in the y-intercept equals (best y-intercept - worst y-intercept)
How do you find the percentage uncertainty in a y-intercept?
percentage uncertainty = (best y-intercept - worst y-intercept) / best y-intercept X 100
What is an order of magnitude?
Powers of ten which describes the size of an object, and which can be also used to compare the sizes of objects
What is the order of magnitude of the diameter of a nucleus?
10^-15
What is estimation?
Approximate values of quantities that can be used to make comparisons or if a calculated value is reasonable
